COOPERATIVE RESEARCH REPORT

No. 47

REPORT OF THE ICES WORKING GROUP

on the

BL0DEN TAGGING EXPERIMENT. 1969/70

https://doi.org/10.17895/ices.pub.6091

International Council for the Exploration of the

Sea Charlottenlund Slot. DK-2920 Charlottenlund

Denmark

May 1975

CONTENTS

1 Introduction

1.1 Experimental design

2 The liberations ............................ ..... .

3

2.1 2.2

2. 3 2.4

The tagging operations ................... . The hydrographic conditions during the tagging experiment ............................. . Tagging mortality experiments ............ . Effective liberations ..................... .

Recaptures

3.1 3.2

3.3

Commercial statistics .................... . Analysis of returns from the fishery for juveniles ................................ .

3.2.1 The Petersen method for stock size estimation ...................... .

3. 2. 2 Test of equal catchability of tagged fish ............................ .

3. 2. 3 Number of recaptures per unit effort. 3. 2. 4 Estimation of catchability coefficient.

Analysis of returns from the fisheries for adults ....... ......... . ...... ..... ..... . .

4 The model ..................................... .

5 Discussion

6 References

Page

1

2

3

4

14 15 18

25

25

49

49

54 55 57

57

60

66

69

Appendices

I

II

III

IV

V

VI

VII

VIII

IX

History of the Bl¢'den Tagging Experiment

Memorandum on the Bl¢'den Tagging Experiment from the President and General Secretary of ICES

Report of the Working Group on the Bl¢'den Tagging Experiment, 20-22 January 1969 .............. .

Instructions for the Supervisor of the Blf!{den Tagging Experiment ......................... .

The Scientific Working Groups and the Management Committee .................................. .

"Gerda Marie": tagging and sampling log ....... .

Tagging mortality experiments ................ .

Length distributions from industrial herring land -ings in Denmark ............................. .

Bl¢'den Tagging Experiment: the model, by M. Nicholson, Marine Laboratory, Aberdeen

Page

70

74

77

87

89

91

120

126

129

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1 Introduction

In 1966 the North-East Atlantic Fisheries Commission asked the Liaison Committee of ICES for guidance regarding the effects of measures proposed to conserve the Downs stock. In particular it enquired into the effect of regulation of the Blf6den industrial herring fishery and the conse­quent effects on the Downs stock. From previous international tagging experiments it had been calculated that in 1957 and 1958 the juvenile fishery removed about 16-19 per cent of the stock per annum. Because of the limi­ted extent of these experiments and the changed nature of the juvenile fishery, it was proposed that a new tagging experiment should be made, spreading the liberations of tagged herring over a longer period and at a higher rate of tagging.

The history of the project is outlined in Appendix I and the detailed plans are given in Appendix II. Because of delays in arranging the financing of the experiment, and changes in the North Sea fisheries since the inception of the idea in 1967, the object of the proposed experiment was not restricted to Downs herring alone but included the total juvenile stock wherever it occurred.

The Blf6den Herring Tagging Experiment took place during the period July 1969 to March 1970. Tagged herring were expected to remain in the area of the juvenile herring fishery until early 1971 at least. The Working Group met in March 1971 ( Anon. 1971) to examine the material so far available and to consider useful methods of analysing the data. The develop­ment of a more extensive model of dispersion than that used for the 1957-58 experiments was considered essential. From these taggings, a higher per­centage of tagged fish had then been recaptured, over a relatively long period, than from those of 1957 and 1958 (Aasen et al. 1961). It was decided to meet again at ICES headquarters prior to the Statutory Meeting in September 1971,

· to further consider the available data and to discuss the type of dispersion model required.

The Marine Laboratory, Aberdeen offered the assistance of a mathe­matician/programmer and the facilities of a computer of adequate capacity. A time-table was drawn up for transference of the data from computer files in Copenhagen to Aberdeen and for the development of the progra~, which was expected to be operational during autumn 1972. It was agreed that the Group should meet when output from the computer was available.

The development of the computer program took longer than anticipated, the first outputs not being available before June 197 3, when the Working Group was convened. The preliminary results from the dispersion model were dis­cussed and a number of modifications were proposed. A report was presented to the Pelagic Fish (Northern) Committee at the ICES 1973 Statutory Meeting, dealing basically with the returns from the juvenile fishery. Stock sizes and fishing mortality rates were derived.

As considerable numbers of tags had already been recovered from the adult fisheries in the northern North Sea and west of the Orkneys, and since some were still being reported from the 197 3 season, the final meeting of the Working Group was delayed until May 1974, by which time these latest returns would be processed and the new outputs from the dispersion model would be available.

- 2 -

Mr J. J. Zijlstra was Chairman of the Working Group from its incep­tion until September 1971, when he resigned from the Netherlands Institute for Fisheries Research to take up a university post. Mr A. C. Burd suc­ceeded him as Chairman. The parallel Managing Committee for the Bl¢'den Tagging Experiment was headed by Mr Th. J. Tienstra.

Mr J. M¢'ller Christensen, in his capacity as ICES Statistician from 1969 to 197 3, acted as Secretary to the Working Group. He was responsible for the bulk of the day-to-day administration of the experiment, including the handling and processing of all the tag release and recapture data.

The responsibility of conducting the entire tagging experiment on board MV "Gerda Marie" rested with Mr Gunnleiv Sangolt, of the Institute of Marine Research, Bergen, who was assisted by two taggers recruited from the crew of "Gerda Marie" - Erling Storeb¢' and Lars Kalve - and by temporary Technical Assistant Kjell Str¢'msnes. It will be evident from several dif­ferent sections of this Report that Mr Sangolt's task as Supervisor was made extremely difficult by bad weather, abnormal hydrographic conditions, and above all by the scarcity of herring. That the outcome of the experiment was as successful as it was, is due entirely to his energy and resourcefulness in the face of constant setbacks and disappointments.

1. 1 Experimental design

It was considered necessary that tagging should be distributed over the widest possible area during the experiment. Four tagging areas were defined (Figure 1 of Appendix III), and it was intended that in each month tagged herring should be liberated in each area. A Norwegian purse seiner, MV "Gerda Marie", was chartered as the catching and tagging vessel. At various times assistance in searching for herring shoals was given by research ves-

.sels from Denmark, France, the Federal Republic of Germany, Norway, Poland, the Netherlands, the United Kingdom and Sweden.

Mr G. Sangolt, a member of the staff of the Institute of Marine Research, Bergen, Norway was Supervisor on board the ship, and the two tagging teams, whose membership was kept unchanged, consisted of crew members. During the first two months of the experiment the herring were tagged from keep nets alongside the ship; for the remainder of the experiment they were-transfer­red to flooded hold tanks aboard the vessel. The tags used were small "sprat 11-type internal magnetic tags. The ultimate aim was to release 100 000 tagged fish, but due to scarcity of herring only 57 496 fish were released.

Samples of fish from each tagging experiment were measured and pre­served for subsequent analysis for age and racial characters. Special arrangements were made for the biological sampling of the commercial catches in Esbjerg during the period when tags were being recaptured. The success of the racial analysis would be dependent on adequate data being available on the meristic characters of the 1967 and 1968 year-classes as spawning fish. A separate report will be prepared on these data, which are

. being processed outside the budget of the tagging experiment.

In addition, all countries processing herring for meal were asked to col -lect biological data on the herring being processed and to improve their

- 3 -

collection of detailed catch and effort statistics by fishing position, which, in some cases, were not considered adequate for analysis of the tagging experi­ment results. It was stressed that all major plants handling herring catches from the North Sea and Skagerak should be fitted with magnets and that the efficiency of recovery of tags by these magnets should be regularly tested.

In addition to effecting the tagged herring liberations, six experiments were performed over 3-5 days to try to determine the mortality caused by tagging.

2 The liberations

The execution of the plan for the distribution of tagged herring through­out the North Sea and the Skagerak was unsuccessful. Primarily this was due to the scarcity of herring of a suitable size for tagging (15-23 cm).

In the planning of the experiment it was presumed that the purse- seining operations would be limited to wind strengths below Beaufort force 4, and this proved to be correct. From a study of meteorological conditions, an average of 9-12 working days per month over the period July to March could be expec­ted. This level of working was achieved in July to September, but in November work was possible on only four isolated days, and long periods of gales occurred in January, February and March.

Despite considerable searching by "Gerda Marie" and research vessels, the tagging locations were restricted both in time and area. The positions in which tagged fish were liberated are shown in Figure 2.1.

62° ~ 0 2· o· 2·

61 •. 0

IJ.(l •

60° i: 0

59° Q

a·{! o·,.

58°

57°

56°

55°

5~ 0

53°

Figure 2. 1 Locations of tagging positions.

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2.1 The tagging operations

The fishing and tagging operations were carried out by the 153 ft Norwegian purse seiner "Gerda Marie" (H-32-AV). The vessel was built in 1967 and was fully equipped with sonar, echo-sounder, radar, Decca naviga­tion and Loran. Her two motor auxiliary boats both had Basdic sonars and echo-sounders and, being equipped with lights, were well suited for the tagging operations. "Gerda Marie' '. had three refrigerated seawater tanks of about 60 cubic metres capacity, and deep-freezing and cold-storage capacity. She was, at the time, one of the most modern in the Norwegian fleet. The skipper, Mr Martin Saele, was very experienced, as was the crew of nine men. In addition, two other crew members were employed especially as taggers and to assist the ICES Supervisor.

Initially, herring were transferred from the purse seine to keep nets by weighting down the floats and allowing fish to swim into keep nets. The fish were then tagged from the auxiliary motor boats out of the keep nets. After some weeks it was found that by transferring the herring from the purse seine to the large seawater tanks they could be kept in good condition for tagging. For this transfer a commercial landing net was lined with can­vas nearly to the iron lifting frame. This brailing net lifted about 1 tonne of water, and 50-150 kg of herring could be transferred from the purse seine to the ship's tanks in each lift. Fish for tagging were transferred in a similar manner from the ship's tanks to a deck tank of 2 tonnes capacity, from which a 15 cm diameter plastic pipe led over the side to near the sea surface. The tagged herring were released down this pipe in a stream of running sea water.

Information on the location of Norwegian, Swedish and Danish herring fisheries was transmitted to "Gerda Marie" by ICES headquarters. In addi­tion it was arranged that a research vessel would assist in echo surveys and other tasks throughout the eight months of the charter. Various countries offered vessels to cover seven months (see below); in February 1970 the area would be covered by the vessels taking part in the ICES Young Herring Surveys.

France Poland Denmark Poland Netherlands Norway Federal Republic of Germany

July 1969 August 1969 September 1969 October 1969 November 1969 December 1969 January 1970

In order to meet the requirement to spread taggings over the area of distribution of juvenile herring, the North Sea was divided up into a number of squares (Appendix Ill, Figure 1). While "Gerda Marie" was searching and tagging in one area it was intended that the other areas be searched by the assisting research vessel, to locate fish suitable for tagging. On completion of a tag liberation in one area it was intended that "Gerda Marie" should then move to one of the other areas to make a liberation.

Mr Sangolt's day-book and his regular progress reports to ICES have been used to compile the following summary of the progress in the tagging operation. A record of all purse-seine shots is given in Table 2.1.

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Table 2.1 Log of tag liberations and purse-seine shots by MV "Gerda Marie"

Date Position Wind Beaufort Herring Comments Tags Expt direc- scale catch liberated no.

latitude longitude tion (tonnes) N E

1969

21 July 57°40' 10°14• WSW 5 nil Current too strong 22 July 57 08 08 00 w 3 0.05 0. 05 tonne small mackerel 23 July 57 52 10 14 w 3 35 fish Current too strong 24 July 57 53 10 59 N 2 £.· 100 0. 5 tonne mackerel

fish 57 52 10 30 N 2 3 Calm sea: fog 1 996 1

31 July 55 02 05 36 N 3 3 1 800 2 1 August 55 04 05 56 ESE 3 1 2 000 3 4 August 54 28 05 46 Var. 1 nil

54 41 05 30 S'E 1 0.5 4 000 4 7 August 54 57 05 20 N 3 20 Delivered to Esbjerg 2 000 5

19 August 56 25 06 33 S'W 3-4 0.5 Mixed sprats and herring 2 000 6 28 August 57 34 11 38 w 4 0.25 0. 02 tonne sprats 2 000 7

5 September 56 28 06 45 w 3-4 1.5 2 000 8 8 September 56 25 06 54 NW 2 10 Some sprats and mackerel 2 000 9 9 September 56 59 07 17 ESE 3 1. 5 2 000 10

11 September 55 01 06 21 SW 3-4 some 200 kg sprats, 1% herring

15 September 55 01 07 03 NE 4 nil } { Strong N current, seining diffi-

1100 11 55 01 07 03 NE 4 0.1 cult: small mackerel and sprats 19 September 54 13 03 40 E 3 0.02 Mixed sprats 1 600 12 · 6 October 57 35 11 22 nil Few 0-group Norway pout

7 October 57 50 11 05 nil Seine net wrecked 10 October

from commercial catch in Oslofjord Released 59o35•N 10°39'E l 000 13

15 October Released 58°05'N 06°31 'E 1 000 14 22 October 56 30 07 02 Var. l 5 Fish held overnight 2 000 15 23 October Released 56°05'N 07°15'E 2 000 16 24 October Released 55°28 'N 07°15'E 2 000 17 26 November 56 40 06 32 NE 2-3 l 3 000 18

3 December 57 56 11 05 NNW 3 nil 7 tonnes small horse mackerel 11 December 55 06 04 34 SW 4 30 Large herring 2 000 19

1970

7 January 55 05 04 23 N 3 8 8 Norwegian purse seiners 2 000 20 8 January 54 32 04 27 SE 4-5 2 2 000 21

12 January 54 29 06 12 N l 3 Part catch lost due to current 2 000 22 13 January 54 43 06 31 N l 0.4 Main catch lost 600 23

54 45 06 34 N l 70 Net sank with weight of catch 2 400 24 14 January 55 11 06 14 SE 3-4 nil 15 tonnes sprats 27 January 55 35 05 54 Var. 2 nil Too close to bottom 11 February 54 11 05 06 s 1-2 8 2 000 25 12 February 54 01 04 54 NNE 1-2 2 3 000 26 24 February 54 14 05 31 0 Too close to bottom 25 February 53 46 03 59 nil 7. 5 tonnes sprats 26 February } 54 41 05 56 N 3 1 Some held overnight { 2 000 27 27 February 2 000 28 27 February 2 000 29

----TOTAL 57 496

- 6 -

July: "Gerda Marie" left Esbjerg on 18 July, together with RV "Thalassa". In accordance with the operational programme 11Thalassa" searched from Esbjerg, over the Cleaver Bank and Silver Pit, north-west to the Farn Deeps and east to Skagen. No herring were found immediately east of the Dogger Bank,. but a mixture of small herring and sprat was found on the southern Bliden ground and near the Silver Pit. Little was found in the north­western area and so "Thalassa" went to join "Gerda Marie" off Skagen. Simplified cruise tracks of the two ships are shown in Figure 2. 2.

"Gerda Marie" started to search for herring off the Holmen Ground. When weather permitted, a number of shots were made in the positions indi­cated on the chart. The first successful shot on 24 July was accomplished after much time spent in chasing shoals, with which it was difficult to main­tain contact. This area off Skagen appeared to be the only place in the North Sea, apart from the Shetlands, where herring were being caught. No herring had been landed by the Danish industrial fishery in Esbjerg during the week, and one Norwegian purse seiner had unsuccessfully searched the area from the Holmen Ground to Coral Bank. "Thalassa" took herring on board in her large tanks, in order to make a tagging mortality experiment.

"Thalassa" then searched the German Bight and identified an area con­taining a mixture of sprats and herring. "Gerda Marie" headed for this area, but by then the sea conditions were unsuitable for purse seining. In improving weather, however, a successful shot was made. Because of the presence of a sharp temperature discontinuity, only poor signals were obtained on the sonar and the shoal had to be located by echo-sounder.

In the 12 days available for fishing in July, 4 days were lost due to weather; six shots were made, from which two tag liberations resulted.

August: "Thalassa" was replaced by the Polish research vessel "GD_N 100" as assisting vessel, and she joined "Gerda Marie" in the southern Bl~den area. The searching program.me is shown by a generalized track chart in Figure 2. 3.

The records of "GDN 100" and "Gerda Marie", and reports from com­mercial vessels early in the month showed that there was an area of about 40 square miles in the southern Bliden where small herring occurred. Most of the traces were small and on the bottom, and were not suitable for purse seining; hand-lining indicated that some of these traces were mackerel. A Norwegian scouting vessel had searched the Holmen Ground and the Great and Little Fisher Banks without finding herring.

During the period 7-20 August "Gerda Marie" and "GDN 100" worked in an area north and west of Esbjerg. During searching the bas-boat was lowered on several occasions to try to identify fish traces. Close contact was kept with fishing boats, to obtain reports on herring. Only two catches were made and 4 000 herring were tagged. An attempt was made to carry out a mortality experiment, but the keep net was lost in deteriorating weather.

By the end of the month information indicated that Swedish vessels were catching herring off Vinga. The weather was unsuitable for fishing at first, but later a catch of about O. 3 tonne of herring and sprats was made. The fish were tagged in deteriorating weather.

62° lo 20 00 20 lo 60 80 100 12°

. 61°

g IJ,(1•

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59° ~ a~ ~-0

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52° ~ ✓ L -

I --- R.V. Thalosso ® Togging pas it ion

51°~ ~r-- p Other Purse Seine shots

50°

Figure 2. 2 Simplified cruise tracks of MV "Gerda Marie" and French research vessel "Thalassa".

62° lo 20 00 20 lo 60 80 100 12°

61°

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0

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53° August 1969 --- Gdn 100

52° - Gerda Morie ® Togging position

51° p Other Purse Seine

1'-. shots

50°

Figure 2. 3 Simplified cruise tracks of MV "Gerda Marie" and the Polish research vessel "GDN 100".

-.::i

- 8 -

Of the 23 days available for fishing during this month, 4 days were lost due to weather, but because of the scarcity of fish only five liberations could be achieved.

September: Because of weather conditions little searching could be achieved in the first few days of the month. Radio contact was made with both RV "Anton Dohrn" and a Soviet research vessel. "Anton Dohrn", work­ing near the Dogger, reported that herring were very scarce, and the Soviet vessel reported herring mixed with sprats to the south-west of the Dogger. Good herring landings were made in Esbjerg from an area40-180 miles WSW to WNW of the port. "Gerda Marie" went to the area and caught about 1. 5 tonnes. A mortality experiment was conducted in the "Gerda Marie" tanks, while the ship remained at anchor.

The fish in this area were in very small shoals and were poor sonar targets. At times the shoals were unstable, moving vertically through the water column. In addition, a strong current made purse seining difficult and several blank shots were made.

"Gerda Marie" went further west and passed over the Cleaver Bank on the 20th. Very few herring traces were seen. Near the Greater Silver Pit some fish traces were found but, because of a strong north-west current, no shot was made. Bad weather prevented any further work before the end of the month. The area searched is shown in Figure 2. 4.

Of the 28 days available for work, 10 days were lost by poor weather, mostly at the end of the month. Five successful herring catches were made, and two other shots were made without catching herring.

October: In improved weather "Gerda Marie" searched towards Hanstholmen without finding fish. It was decided to join "GDN 100" in the Skagerak, where herring were reported. On a number of occasions the bas­boat was lowered on sonar targets, only for them to disappear. Later, numerous small targets were found and one shot resulted in a catch of 0-group Norway pout. On 7 October the seine net fouled the propeller and "Gerda Marie" had to be towed to Skagen. The seine net was not repairable and a replacement was ordered from Norway.

While this net was being prepared "Gerda Marie" went to the Oslofjord, where herring were obtained from the fishermen and a large tagging mortality experiment was commenced. During the period up to the 21st, when "Gerda Marie" recommenced searching, the Polish research vessel "GDN 100" had searched the area shown in Figure 2. 5. Targets had been found in the area indicated and "Gerda Marie" made course in that direction. The shoals were very active and only after dusk did the fish become quieter and a successful purse-seine shot was made. "GDN 100" joined "Gerda Marie" at the tagging location and a mortality experiment was commenced with a floating keep net. However, the weather deteriorated and "Gerda Marie" moved south with herring in her tanks. The weather became so bad that the ships sought shelter. The keep net could not be recovered.

During October 9 days were lost from weather, another 8 days were lost due to the trouble with the purse seine, and only 8 days were available for tagging experiments.

620 4 0 20

61° g

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59° ~ 0 ~e 0

17 58°

57°

56°

55°

54°

53°

52°

51°

50°

00 20 40 60 Bo 10°

September 1969 Oona Gerda Marie

® Tagging position

12°

P Other Purse Seine shots

Figure 2. 4 Simplified cruise tracks of MV "Gerda Marie" and Danish research vessel "Dana".

620 4 0 20 00

61° · g

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60° ~ ~· C)

~.,o 59' ~fe

58°

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October 1969 Gdn 100 Gerda Marie

12°

® Tagging positions P Other Purse Seine

shots

Figure 2. 5 Simplified cruise tracks of MV "Gerda Marie" and Polish research vessel "GDN 100".

co

- 10 -

November: The Dutch research vessel "Willem Beukelsz" assisted in searching on the few days allowed by the weather (Figure 2. 6) . On her way home on the 25th the ship found some targets and on the 26th "Gerda Marie", after a number of unsuccessful attempts to locate the shoals with the bas­boat, succeeded in taking a catch of herring. Tagging began, but by midnight the gales had returned and the ship went to port. During this month 26 days were lost due to weather.

December: The Norwegian search vessel 11Havdr(i{n 11 reported targets near Skagen and, after some time spent searching, a shot was made with a catch of 7 tonnes of small horse mackerel. Commercial catches of herring in Skagen were far below the average for that period. RV "Johan Hjort" searched the Egersund area and reported no herring targets. "Havdrin"found herring traces near the bottom close to the Swedish coast where Swedish boats had made catches. "Gerda Marie" went to the area but was instructed from ICES to return to the North Sea to try to release more herring there, and both "Havdrin" and "Gerda Marie" worked west into the North Sea (Figure 2. 7).

Small sonar targets were located on several occasions. The bas-boat was lowered but the traces were not identified as herring. "Havdrin" searched in the southern Bliden ground and eventually found a shoal on the bottom. "Gerda Marie" joined and in the evening, when the shoal lifted, 30 tonnes were taken. "Gerda Marie" searched northwards, in deteriorating weather, and on the 18th sailed for Norway.

During December 5 days were lost due to weather; the rest of the available 18 days were spent steaming and searching, with only 2 days' actual tagging.

January: The ship returned to the area of the last catch made in December. Contacts were made with Norwegian purse seiners. One vessel had taken 200 tonnes of herring and an attempt was made to transfer part of the catch to "Gerda Marie", but because of the size of the catch the fish were in poor condition. Twenty-five Norwegian purse seiners had gathered in the area and caught about 1 800 tonnes. "Gerda Marie" later made two shots and completed tagging operations before the weather became too bad for working.

During 9 January the ship made for Helgoland and presented the remaining live herring from the tanks to the Aquarium. "Anton Dohrn" had searched the Silver Pit area and western Dogger without recording any herring, and a Norwegian purse seiner had searched from Turbot Bank to Clay Deep without locating fish. "Gerda Marie" searched towards White

·Bank and found small traces, catching about 3 tonnes. On the 13th two shots were made on large shoals and enough herring for tagging were secured.

"Anton Dohrn" had made an extensive survey (Figure 2. 8). The distri -bution of herring seemed to have changed from the previous month, when shoals were very small and scattered. About 50 Norwegian purse seiners were operating in the Clay Deep area and many good catches were taken.

620 lo

61°

60° I-~

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57°

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53°

st

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November 1969 W. Beukelsz Gerda Marie

e Tagging positions

Figure 2. 6 Simplified cruise tracks of MV "Gerda Marie" and Dutch research vessel "Willem Beukelsz".

62ol 0 2° 0° 2° l 0 6° 8° 10° 12°

61°

60° I-~

59° I- 0~e

17'° 58°

57°

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December 1969 R.V. Johan Hjort M. V. Havdrin Gerda Marie

® Tagging position P Other Purse Seine

shots

Figure 2. 7 Simplified cruise tracks of MV "Gerda Marie" and Norwegian research vessel "Johan Hjort" and MV "Havdr~n".

..... .....

- 12 -

Gales hampered the work from 15 to 27 January, but searching was carried out along the Danish coast between Esbjerg and Hvidesande, west­ward towards Clay Deep, and later northwards. No suitable targets were seen. From fishing reports and the work of "Anton Dohrn" the general pic­ture was that herring were limited to the area 54°00'N to 55°30'N and 03°30'E to 6°00'E.

During this month about 16 days were lost due to weather, especially in the last part of January. Only 9 working days were achieved.

February: "Gerda Marie" resumed work in the western part of Skagerak but later investigated the White Bank area, assisted by RV "Tridens". Because of storms, the activity of both ships was much reduced and very few sonar targets were detected. Some very active targets were recorded which could not be pursed. fuformation was received that many, trawlers were working in the Puzzle Hole area with Faroese purse seiners, and some information came from the International Young Herring Survey. Two good catches were made before the winds increased and "Gerda Marie" went to IJmuiden. From 16 February she searched up the Dutch coast and on the White Bank (Figure 2. 9). The Norwegian purse seiners had searched the area between 54°00'N and 55°00'N and 04°30'E to 06°00'E without finding any suitable targets.

Possible herring targets in the Helgoland area were detected close to t~e bottom, but, because of the strength of the current, it was considered doubtful if successful shots were possible.

A Norwegian purse seiner reported a catch of herring, and "Gerda Marie" went towards this position and succeeded in catching 1 tonne of small herring suitable for tagging (Experiment 27). With the weather deteriorating the ship went to Esbjerg. Of the 23 days available for fishing, about half the time was lost due to storms, giving impossible working conditions; 4 days were spent tagging.

March: "Gerda Marie" searched towards the White Bank and detected a few small scattered traces. Swedish and Norwegian herring vessels were reported as having left the southern North Sea. The weather againdeteriora­ted and the ship went to Esbjerg. She sailed again on the 9th, but with deteriorating weather and the end of the charter period approaching, she left the area and returned to Bergen on 12 March (Figure 2.10).

Of the 12 working days available, 5 were lost due to weather, and no tagging was done during the month.

During the entire period in which "Gerda Marie" was used for tagging, about half the available time was lost due to adverse weather conditions. The rest of the time would, however, have been sufficient for the tagging of 100 000 herring as intended, but the scarcity of herring prevented this. Very extensive surveys of the areas were carried out, and at all times the tagging vessel made use of information from research vessels, commercial fishing boats and reports of landings.

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51°~ ~ l -- p Other Purse Seine shots

50° I-/ I I I I I I I I I

Figure 2. 8 Simplified cruise tracks of MV "Gerda Marie" and German research vessel "Anton Dohrn".

62° C 20 00 20 40 60 80 10° 12°

61°

60° ~ g

IJ,O·

~-0

59° r 0~ <>-o

58°

57°

56° ~~ \ b t: _r,\-l

55°

54 °

53°

s2°

S1°

50°

February 1970 - Gerda Marie

~ Tagging positions P Other Purse Seine

shots

Figure 2. 9 Simplified cruise track of MV "Gerda Marie", February 1970. The area between latitudes 52 and 58°N was covered by vessels working in the ICES Young Herring Survey.

f--& w

61 °

60°

59°

sa·

56°

- 14 -

March 1970 Gerda Mar ie

Figure 2.10 Simplified cruise track of MV "Gerda Marie", March 1970. The area between latitudes 52 and 58°N was covered by ves­sels working in the ICES Young Herring Survey.

2. 2 The hydrographic conditions during the tagging experiment

In order to assess if environmental conditions could be affecting the behaviour and abundance of the young herring, the monthly surface tempera­tures and salinities during the Bl!iden Tagging Experiment were compared with the 1905-54 monthly means (ICES 1962).

In July 1969 the surface temperatures in the Skagerak and in the central North Sea were higher than the long-term mean by about 1 deg C; off the north Jutland coast the surface temperature was below the long-term mean by about the same value. The deviations in salinity followed the same pattern.

With the exception of the area from the English east coast to about 1 °E the surface temperatures in August were far above the long-term mean. In the central North Sea and off the east coast of north Jutland (Experiment 7) the deviation was about +2 deg C, increasing to +4 deg C along the south-west coast of Norway . The Bl!iden area, where Experiments 3 to 6 had been con­ducted, was notable for a deviation of about +3 deg C. The surface salinity was about normal compared with the long-term mean. In September 1969 again (Experiments 8 to 12) positive sea surface temperature deviations were recorded (between 0. 5 and 1 deg C), but salinity was below normal off west Jutland (by -0. 7 to 2. o0 /oo) and similar to the mean in the southern Dogger area.

- 15 -

With positive deviations in surface temperature recorded in this period there occurred a well developed thermocline. On several occasions during these months, fish shoals were recorded below a strong thermocline (RV "Thalassa's" log book and "Gerda Marie's" day book). The spatial extent of this thermocline and the low bottom temperatures were exceptional, as pointed out by Becker (1969). The surface and bottom temperature dif­ferences reached a maximum of 12-13 deg C in August, decreased to 5-10 deg C in September and further to 1-6 deg C in the beginning of October. From that time the turnover took place, caused by strong gales (up to force 9-12 Beaufort), resulting in a progressive homogenization of the water column.

The very extensive distribution of cold bottom water south-east of the Dogger is also likely to have affected the distribution of the young herring in that area. As the densest concentrations are usually found in the high tem­perature gradient, i.e. neither in the very cold nor very warm bottom water, an unusually larger area of suitable temperature conditions was available in August and September 1969. This is probably reflected in the scattered occurrences of young herring from the Jutland Reef and into the Cleaver Bank region.

This abnormal hydrographic situation probably affected the acoustic performance of the sonar during the first three months of the experiment. It may have thus reduced the recording power and effectiveness at catching of the purse seiner.

In October (Experiments 14 to 17), sea surface temperature and sali -nity show no substantial difference from the long-term mean. However, in November (Experiment 18), the sea surface temperature was about 2 deg C above the long-term mean in the Bl¢'den area. The surface salinity showed no marked difference from the long-term mean.

In December 1969 and in January 1970 (Experiments 19 and 20 to 24) a core of colder water had been observed in the central North Sea, which deviated about 2 deg C below the long-term January mean. But in February 1970 (Experiments 25 to 29), sea surface temperature and salinity had returned to normal.

It may be concluded that the hydrographic regime during, at least, the first three months of the experiment were somewhat abnormal. This may well have affected the catchability of the herring.

2. 3 Tagging mortality experiments

One essential refinement over the 1957 /58 experiment was the plan for the experiment on mortality due to tagging. It was proposed that, "Gerda Marie" having made the catch and the teams having effected the tagging, the assisting research vessels should stand by keep nets and monitor the morta­lity during the periods of the experiments.

"Gerda Marie" made her first tagging on 25 July 1969 and RV "Thalassa" placed 99 tagged herring and 104 unmarked in her tanks aboard the ship. ·According to the standard instruction, the fish had been measured on tagging, and the non-tagged fish had also been measured. The numbers

- 16 -

of dead fish found each day are shown in Table 2. 2.

Table 2. 2 Daily mortality - "Thalassa" experiment

Numbers of dead fish

Tagged Untagged

1 1 1 2 4 4 3 7 3

4 2 4 5 7 2

Total 21 14

Mr C. Nedelec, the scientist in charge of RV "Thalassa", reported that the majority of the dead fish (both tagged and untagged) had large lesions on the skin on the back. He suggested that these were caused by the handling during measuring. As the fish liberated to the sea were not being measured on tag­ging, he suggested that it was more logical not to measure those in the mortality experiments. Instructions were issued to Mr Sangolt in conformity with Mr Nedelec 's suggestion.

The "Gerda Marie" mortality experiments were conducted either in flooded hold tanks on board the ship or in keep nets alongside. A known number of tagged and untagged fish were placed in the experimental environ­ments and after 3 or 5 days the tank or keep nets were emptied and the numbers of survivors tagged by each tagging team were recorded (Appendix VII). The results of these experiments are summarized in Table 2. 3; the results are reasonably consistent between experiments. The mean daily percentage mortalities, excluding Experiment 5, were:

Untagged Team 1 Team 2

4.83% 5. 36% 9.40%

- 17 -

Table 2. 3 Mortality experiments - "Gerda Marie"

Experiments Dates Holding unit Duration Temperature Location (days) (OC)

1B 31 July 1969 Ship's tank 5 18 South of Tail End

2 5 Sept 1969 Ship's tank 5 15 North of Ringkjbbing Ground

3* 9 Oct 1969 Ship's tank and 5 12 Oslofjord keep net

4* 10 Oct 1969 Ship's tank and 5 12 Oslofjord keep net

st 29 Nov 1969 Keep net 3½ 8 Stavanger Fjord

6 7 Jan 1970 Ship's tank 3 6 South of Tail End

Experiments Treatment Total Alive Dead Tag Lost Effective % alive % daily shed liberation mortality

1B Untagged 108 77 31 108 71. 3 5.74 Team 2 100 67 33 5 100 67.0 6.60

2 Untagged 100 78 22 100 78.0 4.40 Team ? 100 68 32 100 68.0 6.40

3* Untagged 172 114 51 7 165 69.1 6.18 Team 1 200 112 73 1 15 185 60.5 7.89 Team 2 200 90 94 2 16 184 48.9 10.22

4 Untagged 100 77 20 3 97 79.4 4.12 Team 1 104 88 16 104 84.6 3.08

st Untagged 100 98 1 1 99 99.0 0.29 Team 1 100 98 2 100 98.0 0.57 Team 2 100 84 12 1 3 96 86 . 6 3. 57

6 Untagged 108 91 12 108 88 . 9 3.70 Team 1 100 83 15 2 98 84.7 5.10 Team 2 100 67 30 2 98 68.4 10.53

* Fish bought from purse seiner in Oslofjord. t This experiment was performed on fish caught on the Monkey Bank and transported to Stavanger Fjord

(27 -hour steam).

- 18 -

The experiments have been summed to obtain estimates of survival rates for fish tagged by teams 1 and 2 (Table 2. 4), omitting Experiment 5.

Table 2. 4 Survival of herring

Number liberated

Survival Percentage Range

Untagged

588

74. 32 69.1-88.9

Tagged

Team 1

387

73.12 60.5-84.7

Team 2

382

58. 90 48.9-86.6

The range of survival in untagged fish is only 19. 8 per cent, while for team 1 the range is 24 . 2 per cent, and 37. 7 per cent for team 2. It is quite probable that the survival in individual groups of liberations may have been much lower than the average values used in the following analysis.

2. 4 Effective liberations

Assuming that there is no further mortality due to tagging beyond the 5 days of the experiments, the total numbers of fish liberated may be adjus­ted to give an effective number of tags liberated. Table 2. 5 gives the numbers of fish tagged by each team and the numbers recaptured.

The mean recapture rate, p, of fish tagged by team 2 relative to team 1 was 0. 7313 ± 0.139, and was calculated from the ratios of percentage recap­tures in Table 2. 5.

Let N .. lJ

= number of fish tagged by team i (i = 1, 2) in experiment j (j = 1-29);

S. = percentage survival after tagging. 1

Taking the percentage survival of team 1 fish in the mortality experiments, the effective liberation, Lij, is

or, in terms of survival of team 2 fish, effective liberation is

(1)

(2)

- 19 -

Table 2. 5 Recaptures and liberations by tagging team to 30 April 1971

Experiments Recaptures Number tagged

Team 1 Team 2 Team 1 + Team 1 Team 2 Team 2

1 95 61 156 996 1 000

2 160 114 274 900 900 3 193 159 252 1 000 1 000 4 282 267 549 2 050 1 950 5 171 98 269 1 050 950 6 59 100 159 1 000 1 000

7 56 50 106 1 000 1 000 8 95 57 152 1 000 1 000 9 151 73 224 1 000 1 000

10 172 109 281 1 000 1 000 11 47 17 64 600 500 12 72 42 114 800 800 13 6 2 8 500 500 14 22 7 29 500 500 15 185 130 315 1 000 1 000 16 200 141 341 1 000 1 000 17 211 165 376 1 000 1 000 18 277 205 482 1 500 1 500 19 105 108 213 1 000 1 000 20 87 87 174 1 000 1 000 21 155 134 289 1 000 1 000 22 65 32 97 1 000 1 000 23 17 8 25 300 300 24 181 154 335 1 200 1 200 25 118 93 211 1 000 1 000 26 134 116 250 1 500 1 500 27 24 26 50 1 000 1 000 28 17 10 27 1 000 1 000 29 30 14 44 1 000 1 000

All 3 387 2 579 5 966 28 896 28 600

Experiments Percentage recapture Effective liberation

Team 1 Team 2 Ratio: Team 1 Team 2 Team 1 +

Team 2 Team 2

Team 1

1 9,54 6,10 0.6394 765 562 1 327 2 17.78 12.67 o. 7126 691 506 1197 3 19. 30 15. 90 o. 8238 768 562 1 330 4 13. 76 13.69 0.9949 1 575 1 096 2 671 5 16.29 10. 32 0.6335 807 534 1 341 6 5.90 10.00 1. 6949 768 562 1 330 7 5.60 5.00 0.8929 768 562 1 330 8 9.50 5. 70 0.6000 768 562 1 330 9 15.10 7. 30 0.4834 768 562 1 330

10 17.20 10. 90 0.6337 768 562 1 330 11 7.83 3.40 0.4342 461 281 742 12 9.00 5.25 o. 5833 615 449 1 064 13 1.20 0.40 0.3333 384 281 665 14 4.40 1.40 0. 3182 384 281 665 15 18.50 13. 00 0.7027 768 562 1 330 16 20.00 14.10 0.7050 768 562 1 330 17 21.10 16. 50 0.7820 768 562 1 330 18 18.47 13.67 o. 7401 1152 843 l 995 19 10.50 10.80 1. 0286 768 562 1 330 20 8.70 8.70 1. 0000 768 562 1 330 21 15.50 12.40 0.8645 768 562 1 330 22 6.50 3. 20 0. 4923 768 562 1 330 23 5.67 2.67 0.4709 230 168 398 24 15.08 12.83 0.8508 922 674 1 596 25 11.80 9. 30 0.7881 768 562 1 330 26 8.93 7.73 0.8656 1 152 843 1 995 27 2.40 2.60 1. 0833 768 562 1 330 28 1. 70 1.00 0.5882 768 562 1 330 29 3. 00 1. 40 0.4667 768 562 1 330

All 11. 72 9.02 22 194 16 072 38 266

- 20 -

Numerically

Llj = 0. 7312 Nlj + 0. 5347 N2j ( 3)

and

(4)

As there is no reason to suppose that one estimate of Si is better than the other, means have been taken of the constants in equations 3 and 4. The fol­lowing relationship was used for calculating Lj, the effective number of fish liberated in each experiment:

L. = 0. 7683 N1

. + O. 5618 N . J J 2J

these numbers are given in Table 2. 5.

The ratio of the percentage recaptured from the two tagging teams varies between O. 3 and 1. 7, with a mean of 0. 7 3. The variations in the ratio do not seem to be associated with time or personnel, but may be regarded as random errors. The calculated Lj, therefore, is used for the entire period.

(5)

The survival of the tagged herring is influenced by a series of factors other than those related to the handling and the injection of the tags. Among these factors are the effects of temperature and salinity changes and the predation of fish and birds. No quantitative assessment can be made of the possible influence of these factors on the newly released herring. According to observations by the taggers, predatory sea birds did not interfere with the release of the tagged herring to any extent.

Previous experience, however, indicates that the environmental effects are likely to be greater during summer than during winter. As outlined in Section 2. 2, the difference between the surface and bottom temperature was 12-13° in August. From this maximum the difference gradually decreased and the water masses became homogeneous in October-November. The tagged herring were released in the surface layer, and during summer these herring would be exposed to a large temperature change if they descended to depths where most herring shoals were observed. In the winter such tern -perature effects did not exist.

During tagging a record was kept of the serial numbers of each fish liberated in each hour from commencement of tagging (Appendix VI). The recaptures for teams 1 and 2 have been grouped by hour of tagging. These have been summarized and expressed as percentages of the total tag releases in Table 2. 6. In Experiment 4, tagging was curtailed after 2 hours and resumed 10 hours later.

Table 2. 6 Tag recaptures by team by hour as percentage of total tag releases

Experiments Number tagged by Hour

1 2 3 4 5

Team 1 Team 2 Team 1 Team 2 Team 1 Team 2 Team 1 Team 2 Team 1 Team 2 Team 1 Team 2 -

1 996 1 000 0.085 0.077 0.080 0.055 0.100 0.015 0.100 0.070 2 900 900 0.157 0.143 0.173 0.100 0.197 0.130 3 1 000 1 000 0.208 0.168 0.195 0.152 0.135 0.125 4* 2 050 1 950 0.124 0.177 0.153 0.106 5 1 050 950 0.160 0.117 0.152 0.082 0.180 0.120 6 1 000 1 000 0.075 0.080 0.055 0.145 0 . 025 0.095 0.020 0,075 0.110 0.090 7 1 000 1 000 0.042 0.050 0.063 0.057 0. 057 0. 037 8 1 000 1 000 0.098 0.065 0.067 o. 037 0.087 0.053 9 1 000 1 000 0.125 0.062 0.142 0.072 0.140 0.070

10 1 000 1 000 0.180 0.096 0.146 0.106 11 600 500 0.053 o. 043 o. 097 0.020 12 800 800 o. 070 0.040 0.080 0.057 0.110 0.060 I

13 500 500 0.013 0.007 0.010 0.000 NI 1-4

14 500 500 0.053 0.013 0.010 0.015 15 1 000 1 000 0.150 0.127 0.178 0.115 0.180 0.107 16 1 000 1 000 0.178 0.135 0.202 0.115 0.150 0.160 17 1 000 1 000 0.212 0.145 0.167 0.167 0.193 0.143 18 1 500 1 500 0.178 0.108 0,172 0,135 0.155 0.100 0.145 0.140 0.210 0.140 19 1 000 1 000 0,102 0.110 0.113 0.103 0.087 0.097 20 1 000 1 000 0.092 0.070 0.070 0,073 0.070 0.107 21 1 000 1 000 0.158 0.135 0.167 0.160 0.123 0.100 22 1 000 1 000 0.055 0.020 0.057 0.043 0.077 0. 037 23 300 300 0.053 0.027 24 1 200 1 200 0,152 0.102 0.163 0.127 0.135 0.125 0.080 0.150 25 1 000 1 000 0.112 0.078 0.120 0.080 0. 100 0,087 26 1 500 1 500 0.122 0.082 0,102 0.122 0.060 o. 038 0.047 0,033 27 1 000 1 000 0.015 0.030 0.040 0.027 0.010 0.017 28 1 000 1 000 0.012 0.005 0.023 0,013 0.013 0. 013 29 1 000 l 000 o. 038 0.008 0.010 0.017 0.040 0,010

Hour 12 13 14 15

4* 0.102 0.120 0.117 0.110 0.170 0,093 0.140 0.123

- 22 -

As can be seen from the table, most liberations were conducted into or beyond the third hour from commencement. Taking all liberations up to and including the third hour, analyses of variance were made within teams to test whether .differences in recovery rate were associated with hour of liberation. The results are given in Table 2. 7. Significant differences for both teams occur between liberations but not between recaptures by hour of liberation.

Table 2. 7 Analysis of variance of recaptures by hour of tagging

Team Source Sum of squares df Mean square

1 Between liberations 0.2060 22 0.00936 Between hours 0.0009 2 0.00045 Residual 0.0149 44 0.00033 Total 0.2218 68

2 Between liberations 0.1243 22 0.00565 Between hours 0.0009 2 0.00045 Residual 0. 0160 44 0.00036 Total 0.1412 68

From each purse -seine 8hot from which herring were to be tagged a sample was taken for length and age analysis. These data are given in Appendix VIII, together with other data relevant to the liberation. From a study of these data and from the positions of the liberations in Figure 2 .1, it was possible to combine some experiments for the purposes of further data analysis (Table 2. 8). The length and age data indicate that in many experi­ments the population of fish tagged could be wholly ascribed to either the 1967 or the 1968 year-class. The mixed liberations tend to an average of 40 per cent, 1967 year-class, and 60 per cent, 1968 year-class.

- 23 -

Table 2. 8 Liberations by position and year-class

Location Liberation Dates Effective Year-liberation class

North of 570 1 25 July 1969 1 327 1967 7 28 Aug 1969 1 330 1967

13 10 Oct 1969 665 1967 14 15 Oct 1969 665 1967

South of 57o and 6 20 Aug 1969 1 330 mixed north of 55o30 1 8-10 5-9 Sept 1969 3 990 1968

15-17 23 Sept- 3 990 1968 4 Oct 1969

18 26 Nov 1969 1 995 1968

South of 55o 30' 2- 5 31 July- 6 539 1967 7 Aug 1969

11 15 Sept 1969 742 1968 12 19 Sept 1969 1 064 mixed 19 11 Dec 1969 1 330 1967 20-23 7-13 Jan 1970 4 388 1967 24 13 Jan 1970 1 596 mixed 25-26 11 Feb 1970 3 325 mixed 27-29 26 Feb 1970 3 990 1968

Total effective liberation 38 266

Throughout the period of the tagging experiments the commercial catches landed in Denmark were monitored for length and age composition of the herring processed. Subsequently, as part of the routine Danish samp­ling programme, only catches at Esbjerg were examined. The data on the age composition of the commercial catches landed in Denmark are given in Table 2. 9, and indicate that although the 1967 year-class was dominant in the fishery in August-September 1969, it became of relatively little importance in the industrial fishery by November 1970. The 1968 year-class was domi­nant in the fishery from October 1969 to July 1970, when the 1969 year-class recruited to the fishery. The comparison of the mean lengths of herring landed in Esbjerg with those of tagged fish (Appendlx VII) shows that the fish caught by "Gerda Marie" throughout the experiment could be taken as repre­sentative of the herring being processed by the Danish fish-meal plants.

Table 2. 9 Age composition of the herring catches corrected for magnet efficiency at Esbjerg, Thyboron and Skagen. The data for Thyboron and Esbjerg have been further corrected to exclude sprat catches. Catch data from Table 3. 2

--Esbjerg Thyboron Skagen

- -Year-class Total Year-class Total Year-class Total

1966 1967 1968 1969 1970 1966 1967 1968 1969 1966 1967 1968 1969 - - - - - - - - - - ----- -- -- -- - - -- -- -- ----

1969

August 25.95 55.07 0.61 - 81. 63 16.34 34.69 0.38 - 51. 41 0.43 9.48 68 . 28 - 78.19 September 19.36 95.92 27.33 - - 142.61 0.85 4.22 1. 20 - 6.27 0.56 4.11 29. 39 - 34. 06 October 6.52 38.06 46. 37 - - 90.95 0.80 4.66 5.67 - 11.13 0.04 1. 21 16.32 - 17.57 November - - - - - - - - - - - 0 0.49 13 . 31 - 13. 80 December - - - - - - - - - - 0 0. 17 13. 02 - 13.19

1970

January 0. 08 3.24 24. 39 0 - 27. 71 - - - - - - 0.29 10 . 51 0 10.80 February 3.32 28.52 130. 03 0 - 161. 87 0.08 0.68 3. 10 0 3.86 - 0.55 7.20 0 7. 75 March 0 0.98 23.24 0 - 24.22 0 0.01 0.35 0 o. 36 - 0. 42 15. 64 0 16.06 April 0.08 11.14 29.77 0 - 40.99 0.00 0.06 0.17 0 0.23 - 0.37 12.27 0 12.64 May 0.30 12.83 54. 34 0 - 67.47 - - - - - - 0. 41 10.59 0 11.00 June - - - - - - - - - - - - 1. 85 10.37 0 12.22

'SI' July - 2.67 34. 86 50.34 - 87.87 - 0.88 11.51 16.62 29.01 - 3.06 6.21 0 9.27 <'-I August 41. 39 70.74 235.36 347 .49 7.74 13. 24 44.04 65.02 0 0.54 90.10 90.64 - - - -

September - 25.39 46 . 23 46.88 - 118.51 - 1.94 3.53 3.58 9.05 - 0. 13 1. 44 34.33 35.90 October - 11.71 13.08 25.51 - 50.30 - 1. 84 2.06 4.01 7.91 - 0 1.18 21. 71 22.89 November - 0.16 0.88 4.96 - 6.00 - 0.04 0.19 1.10 1. 33 - 0 0.19 16.52 16. 71 December 0.41 4.16 14.99 - 19.56 - 0.11 1.12 4.04 5.27 - 0 0.19 10.67 10.86

1971

January - 1.18 8.39 69.26 - 78.83 - 0.07 0.52 4.32 4.91 No further data February - 1. 35 18.43 293.86 - 313. 64 - 0.10 1. 33 21. 27 22.70 March - 0.64 23.49 371.42 - 395.55 - 0.03 1. 22 19.44 20.69 April - 15.09 77.91 171. 88 - 264.88 - 0.19 0.98 2.17 3.94 May - 0.83 4.25 7.13 0 12.21 No further data June July - - 10.96 55.42 o. 79 67 . 17 August - - 18. 37 198.55 62.06 278.98 September October - - 1.00 150.94 71. 08 223.02 November - - 1. 56 41.08 75.15 117. 79 December - - 0 14.37 7.00 21. 37

- 25 -

3 Recaptures

Up to January 1974 a total of 7 280 tags have been returned from processing plants. Of these, some 6 650 tags could be ascribed to a week or month of processing. From January and February 1974 a further 12 tags have been reported. The total represents a recapture rate of about 19 per cent of the effective liberation.

Of the total number of tags returned 76 per cent were reported up to 1 July 1971, by which time most of the tagged fish would have left the area of the fishery for juvenile herrings. The detailed breakdown of returns per month is given in Table 3.1.

Where possible, information was recorded on the location of the fishery in which each tagged herring was caught. Tags recovered from a factory during a short period could sometimes be referred with reasonable accuracy to a particular fishery. For example, in January and February 1970 the Norwegian purse-seine fleet took over 25 000 tonnes of herring from statis­tical rectangle G 09. However, the great majority of the tags, such as those landed in Denmark and Germany, could not be allotted to an area fished. This applies both to the period immediately after tagging, during which the fish remained within the south-eastern North Sea, and also to the later period, when the 1967 and 1968 year-classes had recruited to the adult stocks. In the case of the Danish ports, the recovered tags in this later period could have been· derived from Danish vessels or from Icelandic and Faroese vessels, which made their catches in perhaps very different areas than those fished by Danish trawlers.

The Scottish plants were not capable of recovering tags until rather late in the tagging season, but these plants have since returned tags from the adult fisheries. Herring are processed at the English plants at Hull and Grimsby, but these mainly process offal, and few tags have been recovered from them. Recaptures from Sweden were too few to consider.

3. 1 Commercial statistics

Statistics of the quantities of herring caught in the North Sea and landed for industrial purposes were available from Denmark, Norway and the Federal Republic of Germany. The Danish data are shown by port in Table 3. 2. Repeated measurements of magnet efficiencies at the reduction plants were used to convert the total quantity of herring processed into effective quantities. Using the biological samples taken at Skagen, Thyboron and Esbjerg for age determination, the estimated numbers of herring of different year-classes effectively processed were calculated and these were given in Table 2. 9.

There is a wide range in apparent effective magnet efficiency between the ports. In the case of Skagen, the efficiency of recovery of the individual magnets in a factory line is high, but a number of plants processing herring were not fitted with magnets, thus reducing the weighted magnet efficiency for the port.

Data on the distribution of catch and effort by statistical rectangles are available for Esbjerg where 68-93 per cent of the monthly landings are accoun­ted for, and Skagen where 8 -68 per cent coverage was obtained in individual months. There are no data available from Skagen in 1971.

- 26 -

Table 3.1 Tag recapture per month

Year-class of tagged Year-class of tagged fish fish

1967 1968 Mixed 1967 1968 Mixed

1969 1972

July 6 0 0 January 10 10 1 August 424 0 7 February 5 9 4 September 127 16 61 March 5 3 4 October 96 88 27 April 3 8 2 November 26 7 6 May No returns December 28 6 0 June 19 30 12

July 28 59 21

1970 August 6 11 0 September 0 0 2

January 536 77 21 October 5 5 0 February 451 629 373 November 1 1 1 March 105 217 60 December 6 6 3 April 51 160 45 May 53 160 64

1973 June 97 23 21 July 91 160 53 January 3 0 0 August 106 230 89 February 2 1 1 September 58 140 55 March 3 1 0 October 13 32 16 April 0 1 0 November 27 7 5 May 1 1 0 December 11 37 17 June 1 6 1

July 21 22 8

1971 August 2 10 0 September 4 1 1

January 35 35 10 October 0 1 0 February 8 36 12 November No returns March 29 45 13 December No returns Ap:t;il 14 49 16 May 17 70 14

1974 June 122 21 21 July 142 33 23 January 3 6 2 August 55 57 31 February 0 1 0 September 21 9 6 October 25 11 9 November 12 14 2 Unknown 204 294 132 December 17 20 9

- 27 -

Table 3. 2 . Total catch of herring processed in some Danish ports when 1967 and 1968 year-classes were being exploited. Columns 1 and 4 - total catch corrected for sprat by-catch; Column 7 - total catch in tons processed; Columns 2, 5, 8 - total catch corrected for magnet efficiency; Columns 3, 6, 9 - percentage magnet efficiency (weighted mean)

Esbjerg Thyboron Skagen

1 2 3 4 5 6 7 8 9

1969

August 20 273 6 518 32 8 334 4 106 49 7 402 1 831 25 September 14 698 10 656 72 798 469 59 4 779 1 067 22 October 5 903 4 811 82 750 589 79 2 934 551 19 November 1 860 347 19 December 1127 265 24

1970

January 1 538 1158 75 1 232 260 21 February 9 048 6 533 72 433 155 36 1162 219 19 March 914 690 75 93 10 11 2 331 490 21 April 2 526 2011 80 73 11 15 2 162 327 15 May 4 359 3 232 74 1 787 368 21 June 2 971 713 24 July 5 165 3 939 76 2 032 1 301 64 3 681 644 17 August 15 074 11 705 78 4 184 2 191 52 5 755 1178 20 September 11 557 8 361 72 1 362 639 47 4 948 1 001 20 October 4 177 3 019 72 940 475 51 4 673 822 18 November 260 208 80 69 46 67 2 278 482 21 December 1 294 882 68 458 237 52 2 046 333 16

1971

January 4 615 2 895 63 502 180 36 February 11 439 9 117 80 1 629 660 41 March 16 809 12 943 77 1 732 678 39 April 13 623 11 013 81 387 139 36 May 530 404 76 June July 5 480 4 143 76 August 16 656 13 258 80 September October 1 584 1 204 76 November . 5 380 3 874 72 December 1 574 1141 72

- 28 -

The catches processed in Norway are given in Table 3. 3. Again the weighted magnet efficiency is seen to vary, due mainly to the processing of herring in plants without magnets. Very limited biological sampling has been made on these catches and it is not possible to get estimates of the age composition of the catches by months, other than in some exceptional cir­cumstances. Information was available, however, on the distribution of the catch within ICES divisions (Table 3. 4), and to some extent it was possible to distribute the catch between statistical rectangles.

Landings of herring for industrial purposes by German cutters were presented from two sources for the period June 1969-November 1973 (Table 3. 5). There is some disagreement, not only in the comparisons between months, but also in the annual totals. German recaptures of tags are quite high in some experiments, but no data on the distribution of the German fishery were available.

Charts have been prepared of the distribution of catch by Danish, Norwegian and Scottish vessels for the period July 1969-April 1971 (Figure 3.1-4). This covers the period in which about 76 per cent of the tags were returned.

The distribution of the Danish herring catches shows two rather per­manent areas of fishing, one around the Skaw at the entrance to the Kattegat, and an area in the south-western North Sea - identical with the Bl!llden ground. Fishing the north-western North Sea was more patchy and was mainly carried out in January-April 1970 and again from September 1970 to April 1971.

The Norwegian purse-seine catches were concentrated chiefly in the Skagerak and the north-eastern North Sea in the period July-December 1969. In January-June 1970 additional fishing took place in the central North Sea east of the Danish Bl!llden fishery. In the second half of 1970 a Norwegian fishery around the Shetland-Orkneys developed. Only sporadic landings were taken from the North Sea in the early part of 1971.

The Scottish North Sea herring fishery was mainly concentrated around the Shetland-Orkneys and only a few landings were made in the period October 1969-March 1970 and in the early months of 1971. The largest catches were taken in June-August 1970, when the Scottish herring fishery extended westwards into ICES Statistical Division Via and only minor catches were made east of Shetland.

It is important to note that there was almost no overlap in the area of the fisheries of Norway, Scotland and Denmark. The rate of return of tags from these fisheries is in part a reflection of the emigration from the tagging areas.

In order to facilitate a comparison of the number of tags returned per liberation, the returns have been raised to a standard liberation of 10 000 tags. These values are given in Table 3. 6 for Denmark, Norway and the ,.,,,.'; Federal Republic of Germany. The data are grouped by the year-class of the fish tagged. There are some interesting differences in the pattern of tag returns between the experiments, both in relation to the area of libera -tion and also to the factories or countries from which the tags were recovered.

- 29 -

Table 3. 3 North Sea herring processed in Norway. Total quantity (tonnes) processed (all factories); Effective quantity processed after correction for magnet efficienc~, (overall, weighted mean)

Total Effective % magne,t Total Effective % magnet efficiency efficiency

1969 1972

. July 39 158 22 657 58 January 1 396 1 267 91 August 19 042 13 387 70 February 13 10 77 September 63 41 65 March 888 675 76 October 104 0 0 April 19 15 79 November 84 63 75 May 0 0 0 December . 0 0 0 June 53 292 31 879 60

Total 117 446 71 522 61 July 59 406 34 150 57 August 641 362 56 September 70 42 60

1970 October 40 36 90

January 14 256 11 014 November 0 0 0

77 December 0 0

February 2 416 1 961 81 0

March 0 0 0 Total 115 766 68 435 59 April 317 74 23 May 2 326 1 652 71

1973 June 62 460 43 509 70 July 87 028 54 496 63 June 22 717 16 282 72 August 10 790 6 775 63 July 70 025 48 280 69 September 4 756 3 124 66 August 6 819 6 008 88 October 476 217 46 September 2 474 1 695 69 November 820 179 22 October 231 188 81 December 0 0 0

Total 102 266 72 453 71 Total 185 645 122 997 66

1971

January 93 85 91 February 0 0 0 March 2 0 0 April 200 65 33 May 35 17 49 June 84 412 55 584 66 July 61100 40 684 67 August 15 818 11146 70 September 1 143 948 83 October 23 470 17 960 77 November 215 181 84 December 222 211 95

Total 186 710 126 881 68

- 30 -

Table 3.4 Landings of herring in Norway (in toni;;) from north-west Scotland-northern Ireland, North Sea and

Skagerak, 1969 to 1973

1969 1970

Area Total Area Total

!Va W !Va E !Vb ma Vla !Va W !Va E !Vb Illa

January 11 2 809 2 820 3 338 20 588 20 929

February 19 261 280 2 4 908 4 910 March 201 201 1 51 52 April 301 523 - + 824 911 466 1 377 May 102 6 673 695 7 471 5 734 162 1 593 227 7 715 June 49 044 4 171 68 53 283 7 886 67 334 156 458 3 674 79 508 July 40 709 416 236 41 361 14 082 62 304 13 - 1 866 78 265 August 8 532 217 11 727 20 476 5 494 8 165 354 555 14 569 September 74 74 801 1 783 591 3175 October 108 108 196 56 16 88 357 November 104 70 203 376 949 949 December 80 •l 83 34 34

Total 98 822 15 529 4 13 002 132 700* 27 462 146 397 3 331 27 613 7 037 220 882*

*5 343 tons not specified by month or area *9 042 tons not specified by month or area

1971 1972

Area Area Vla !Va W !Va E !Vb Illa VIIa Total !Va W !:Va E !Vb Illa !Va Total

January 402 1 089 1 491 47 1 404 1 451 February 1 13 14 March 36 88 2 126 22 3 2 037 2 260 April 452 - 60 512 18 18 May 27 - 35 61 June 35 420 61 785 247 97 452 39 653 44 344 197 15 136 55 374 July 39 930 19 185 19 79 59 212 51 055 5 12 242 594 1 907 65 803 August 305 16 774 261 17 340 1 754 307 2 061 September 974 423 1 397 782 4 194 :n 1011 October 56 12 350 ~ 050 5 035 27 091 1 312 1 312 November 369 - 14 383 50 50 December 260 20 280

Not speci-fied by 5 582 949 60 1 029 7 620 month

Total 76 720 112 114 10 442 14 5 961 95 205 345 100 408 50 17 043 1 045 18 428 136 974

1973 Via north-west Scotland-northern Ireland (west of 4°W)

Area !Va W northern North Sea Vla !Va W !Va E !Vb ma Total !Va E northern North Sea

IVb central North Sea January Illa Skagerak February 1 889 1 889 Vila Irish Sea March 614 614 + less than 1 ton April May June 16 763 14 318 77 196 447 31 801 July 13 076 34 719 127 32 839 389 81150 August 623 4 007 32 4 927 9 589 September 95 3 114 40 3 249 October 86 86 November December

Total 30 557 58 747 236 38 002 836 128 378

- 31 -

Table 3. 5 Germany (Federal Republic) - herring landings of cutters fish­ing for industrial purposes in the North Sea (in tons):

January February March April May June July August September October November December

Total

January February March April May June July August September October November December

Total

(1) from the Federal Statistical Office, Wiesbaden; (2) landings split by biological samples (made by the Institute of Coastal and Inland Waters Fishery)

1969 1970 1971

1 2 1 2 1 2

1 449. 3 5 113. 9 4.4 8 520. 4 7 584. 4 36.8 3.5 2 736. 4 2 513. 5 132. 3 72.9 1 002. 0 1116. 0 19.7 2 186. 0 207.7 250.2 21. 5

1 149. 1 1 890. 0 33.3 24.1 152.1 627.3 31. 8 2 929. 5 1 992. 7

3 979.1 5 091. 8 8 054. 7 2 159. 6 4 457. 6 4 071.8 3 289. 0 1 022. 7 3 562. 7 3 903. 0 1 544. 3 1 775. 7

167.2 10.1 966. 2 19.0 89.2

13 794. 8 13 265. 6 33 700. 9 24 485. 7 447. 8 269. 7

1972 1973

1 2 1 2(1)

11. 5 125.5

36. 9 152.1 1 184. 9

549.9 135.6 352.8 23.5 1 7 35. 8 887.2 2 760. 2 1 218. 6 1 714. 8 952.4 1 670. 0 1 322. 6

633.9 848. 0 527.9 390.4 49.8

4 634. 4 2 823. 2 5 686. 7 4 140. 0

Total June-October 5 463. 0 4 140. 0

1 Biological samples only available from June to October.

Table 3.6a Denmark - Esbjerg: recaptures per 10 000 fish tagged by year-class and country

Recapture 1967 year-class 1968 year-class Mixed month

Liberation Liberation Liberation -

1 2-5 7 13 14 19 20-23 8-10 11 15-17 18 27-29 6 12 14 25-26 - -- - - - - -- - ---- - - -- --

1969

July August 549 23 September 101 10 383 19 October 50 22 54 75 56 November 17 8 5 27 5 5 8 47 December

1970

January 6 15 22 13 35 55 8 I

February 7 203 15 105 165 121 268 176 434 351 90 179 670 427 w 1:-.:)

March 11 7 15 25 28 27 120 95 12 28 25 66 April 21 8 15 18 85 40 140 100 43 23 19 56 72 May 28 7 15 30 27 105 54 173 146 12 45 38 44 102 June 8 13 5 10 July 11 8 15 11 98 54 173 155 32 30 28 107 54 August 8 24 30 22 39 120 108 241 180 93 37 66 182 148 September 15 7 9 68 83 146 8 7 9 63 57 October 9 8 15 8 9 38 13 53 65 8 63 24 November 2 10 20 10 2 9 December 3

1971

January 2 February 8 10 13 22 40 8 8 21 March 5 2 3 April 5 15 5 20 53 40 8 9 31 15 ? 3

--Total 15 1 063 60 30 165 278 264 920 592 1 562 1 398 228 737 498 1 272 1 001

Table 3.6b Denmark - Thyboron: recaptures per 10 000 fish tagged by year-class and country

Recapture 1967 year-class 1968 year-class Mixed month

Liberation Liberation Liberation --

1 2-5 7 13 14 19 20-23 8-10 11 15-17 18 27-29 6 12 24 25-26 -- - - - - --

1969

July August 30 September 1 30 23 October 141 50 November December

1970

January February I

March 2 2 w w

April May June July August 3 15 40 27 88 175 30 7 9 50 21 September 5 25 13 48 95 13 23 19 38 30 October 5 12 25 25 3 November December 5 2 5 6 3

1971

January February March April ? 3 2 10 8 15 13 6

--Total 9 15 9 256 40 208 315 43 83 28 132 63

Table 3. 6c Denmark - Hirtshals: recaptures per 10 000 fish tagged by year-class and country

Recapture 1967 year-class 1968 year-class Mixed month

Liberation Liberation Liberation

1 2-5 7 13 14 19 20-23 8-10 11 15-17 18 27-29 6 12 24 25-26 ---

1969

July 30 August 158 September 121 53 22 October 90 2 60 November 22 53 December 22 45 15 15 2

1970

January 15 21 45 41 2 10 8 February 22 61 8 15 38 34 20 10 15 23 47 38 12

c..:i

March 8 20 45 45 41 3 5 8 ~

April 15 23 23 38 29 12 5 5 7 10 38 6

May 23 24 30 30 30 44 22 11 33 15 28 69 June 15 5 8 16 8 July 15 3 August 8 2 15 15 2 5 September 6 3 10 October 4 8 2 12 November 8 2 8 7 9 5 6 3

December 2 25 15 6

1971

January 8 6 8 2 8 20 5 9 13 6 February 1 8 30 2 12 3 5 3 March 2 7 5 5 10 6 April ? 3

- - - - - - --- - - - - -Total 580 182 364 45 90 263 200 70 111 100 68 94 182 36

Table 3. 6d Denmark - Skagen: recaptures per 10 000 fish tagged by year-class and country

Recapture 1967 year-class 1968 year-class Mixed month

Liberation Liberation Liberation

1 2-5 7 13 14 19 20-23 8-10 11 15-17 18 27-29 6 12 24 25-26 -- -

1969

July 15 August 136 September 30 60 October 30 15 2 November 8 15 15 December 37 53 60 13

1970

January 4 8 30 45 2 February 22 23 8 15 15 18 15 10 20 15 19 13 3 I

March 8 4 5 c,.:, i:Jl

April 6 22 7 2 May 8 2 June 8 8 3 July 8 2 August 8 2 7 5 3 September 15 8 8 2 8 October 15 2 8 9 10 2 5 9 November 22 3 15 30 7 5 3 8 13 December 2 8 7 9 20 20 7 19 6 12

1971

January 30 4 8 30 2 2 5 25 6 February 10 March 8 3 8 8 5 10 5 13 3 April 3 15 7 5 10 13 10 ? 22 2 5 5

- - - - - - -Total 422 54 236 45 165 105 75 85 88 70 30 47 45 24

Table 3.6e Norway: recaptures per 10 000 fish tagged by year-class and country

Recapture 1967 year-class 1968 year-class Mixed month

Liberation Liberation Liberation

1 2-5 7 13 14 19 20-23 8-10 11 15-17 18 27-29 6 12 24 25-26 --

1969

July August 15 September October 8 November 2 December

1970

January 8 338 15 466 443 10 60 94 6 I

February 104 8 120 43 33 14 38 15 15 10 69 66 Cl:)

March 33 6 O')

April May 6 15 16 5 2 15 9 19 15 June 30 41 38 68 62 8 5 15 44 21 July 21 40 15 75 59 10 15 19 12 3 August 8 12 38 27 5 15 7 September 8 2 10 5 9 October 8 3 7 9 10 8 3 3 November 2 December

1971

January 13 3 February 2

March 5 5 April 2 5 8 ? 8 3 5

- - - - - - -- - - - - - -Total 98 552 84 15 774 661 105 27 78 40 5 143 132 150 126

Table 3. 6f Federal Republic of Germany, factories 01 + 02: recaptures per 10 000 fish tagged by year-class and country

Recapture 1967 year-class 1968 year-class Mixed month

Liberation Liberation Liberation

1 2-5 7 13 14 19 20-23 8-10 11 15-17 18 27-29 6 12 24 25-26 --- -- - - - --

1969

July August 32 September 33 15 9 October 41 57 November December

1970

January 5 5 13 28 30 February 23 15 15 15 14 78 27 206 301 15 28 88 30 I

March 11 3 43 68 110 155 3 7 19 69 12 i:., -.J

April 4 23 2 22 40 35 35 10 8 9 May June July 3 2 2 10 12 3 August 15 8 8 4 18 13 31 15 10 15 29 38 18 September October November December

1971

January 2 2 February March 2 3 2 8 April 10 7 10 3 ? 2 5 9 6 6

--Total 171 8 15 15 46 25 183 161 431 551 23 68 160 213 72

f :c-

Table 3. 6g Federal Republic of Germany, factory 04: recaptures per 10 000 fish tagged by year-class and country

Recapture 1967 year-class 1968 year-class Mixed month

Liberation Liberation Liberation

1 2-5 7 13 14 19 20-23 8-10 11 15-17 18 27-29 6 12 24 25-26 --

1969

July August 4 September 4 October 11 15 28 November December

1970

January 2 February 2 2 2 13 25 5 9 w March 7 3 2 2 5 6 3 00

April 2 2 2 3 6 6 May 3 5 12 6 June 5 July 2 5 August 8 3 8 7 September 6 2 2 6 6 October 4 2 6 November 2 8 7 3 14 7 10 December 4 7 5 3 9 7 6

1971

January 8 8 5 10 February 13 12 10 March 7 4 7 10 25 5 6 April 2 5 6 6 ?

- - - -- - - --Total 22 58 30 8 34 43 27 75 45 2 15 56 56 39

Table 3. 6h Federal Republic of Germany, factory 07: recaptures per 10 000 fish tagged by year-class and country

Recapture 1967 year-class 1968 year-class Mixed month

Liberation Liberation Liberation

1 2-5 7 13 14 19 20-23 8-10 11 15-17 18 27-29 6 12 24 25-26 - - - - - - -- -- - -- - - - --

1969

July August September October November December

1970

January 7 3 2 5 February 6 2 2 18 35 9 March 6 15 7 5 5 10

t.,.:)

8 10 6 3 ~

April 8 3 8 15 5 5 7 6 3 May June 5 3 July August 2 September 2 9 October 3 10 3 November 2 2 December 4 2

1971

January 2 8 3 February March April ?

- - - -- --Total 15 24 8 30 27 12 33 55 15 38 12 15

- 40 -

Very few of the tags from liberation 1, which was in the Skagerak, were recovered fro:t:n Esbjerg or the German plants . The returns were mainly from Skagen and Hirtshals, whose fleets would be fishing more in that area than in the area fished from Esbjerg and the Federal Republic of Germany. In contrast, tags from liberations 2-5 started to be returned immediately from the Esbjerg and German plants. Only after January were significant numbers returned from Hirtshals, Skagen and Norway. A com­parison between these factories shows that recoveries from the Skagen plants tend to be the latest. This pattern may be explained by a rapid emigration of some of the 1967 year-class taking place, both northerly into the area fished from Hirtshals and westerly into the Norwegian fleet area (Figures 3. 1 and 3. 2). In June, July and August the Norwegian fleet was working either in the Shetland area or in the Egersund region (Figure 3. 3). Later, in the period November 1970 to February 1971, when the Norwegian fishery had more or less ceased, tags were returned from the Danish plants at Esbjerg, Hirtshals and Skagen, the Danish fleet then being recorded as fishing in the north­western North Sea off Shetland and in the traditional Bl¢den area.

The pattern of tag returns from liberation 7, in the Skagerak, is simi -lar to that in liberation 1, which was also made· in this northern area. Liberation 13 was made with fish bought from purse seiners in the Oslofjord and released there, and from it there were very few returns. However, those fish which were transported to Lindesnes before release (liberation 14) are shown to be returned from a wide variety of places.

The fish liberated in Experiments 19 and 20-23 in the southern area in December and January were immediately returned from all Danish, German and Norwegian plants. Relatively low numbers are recovered from the German plants, whose vessels tend to work in the German Bight. This again supports the view that at this time the fish of the 1967 year-class were moving rapidly through the eastern nursery areas, and emigrating from the Bl¢den ground proper.

The factory at Thyboron took a negligible number of the 1967 year-class, in contrast to considerable numbers of the 1968 year-class, in August-October in both 1969 and 1970. The industrial fleet operating from this port consists of smaller vessels which fish a very restricted area close to the port.

Within the liberations of the 1968 year-class a number of contrasts can be seen in the data up to April 1971. Liberations 8-10, 15-17 and 27-29 were all made north of 55°30'. During 1970 these fish were taken in increasing numbers from the southern port of Esbjerg and from the Federal Republic of Germany, particularly in January-April. Tags from these liberations were also returned from the plants at Skagen and Hirtshals . The Norwegian returns contrast in number with those from the 1967 year-class: the numbers returned are comparatively low, and the implication would be that either the Norwegian fleet was avoiding the smaller herring or that these had not moved into the areas fished by the Norwegians.

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Figure 3. 1 Reported locations of fisheries by Danish, Norwegian and Scottish vessels (from ICES Statistical Newsletters and national sources).

21 20

1 9 1 8

17 16

15 1 4 13 12 11 1 0 09 08 07 06 05 04 03 02

0

9

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H 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 2 4 2!i 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 22 23 H 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Figure 3. 2 Reported locations of fisheries by Danish , Norwegian and Scottish vessels (from ICES Statistical Newsletters and national sources) . In February and March 1970 the locations of catches exceeding 400 fish per hour of young herring in the ICES Young Herring Survey are also shown.

I .. N>

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22 23 2t 25 26 27 28 29 30 31 32 33 % JS 36 37 38 39 40 22 23 24 25 26 27 28 29 30 31 32 j) 34 35 36 37 38 39 40 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 LO

Figure 3. 3 Reported locations of fisheries by Danish, Norwegian and Scottish vessels (from ICES Statistical Newsletters and national sources). In February and March 1970 the locations of catches exceeding 400 fish per hour of young herring in the ICES Young Herring Survey are also shown.

21 20

19 1 8

17 16 1 S

H 13 12 11 1 0 09 OB 07 06 05 04 03 02

21

20

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4 3

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- 44 -

Comparing the returns from liberations 8 -10 and 15-17 from the Esbjerg and German factories, it is seen that far greater numbers from the latter liberation were returned in February-April 1970 from these plants than from liberations 8.:...10. This might indicate some difference in the distribution of the liberated fish. From the hydrographic record at the time of the taggings,

it appears that the bottom temperatures were low in the area where libera -tions 8-10 were made. In contrast, in liberations 15-17 the bottom temperatures were much higher.

The distribution of the I-group herring in the North Sea, as described from the ICES Young Herring Surveys in February 1970 and 1971, may be compared with the distribution of the fisheries in the same months. With one exception, there is a good agreement between the locations of the fisheries and the major concentrations of herring. This exception is a major concen­tration of young herring in the Texel area, which is not covered by the industrial fishery. This fishery seldom extends south of 54°N latitude. There is thus the possibility that some of the 1968 tagged fish could have withdrawn from the area of exploitation.

The returns from liberations 11 and 27-29 are remarkable in that none were returned from Hirtshals or Skagen and comparatively very few from Thyboron, Norway or the Federal Republic of Germany. Indeed, this low recapture level has been maintained up to 1974 in the Norwegian catches. This might imply that the effective liberation is less than that calculated. In the case of liberations 27-29 the fish were all caught on 26 February 1970; some were tagged and released that day and the remainder held overnight. Next day a further 4 000 were tagged in two batches. It is possible that this procedure affected survival.

From the evidence of the location of tag returns by fisheries, it can be postulated that the 1968 year-class tended to remain in the central and southern Bl!IS'den area during the greater part of 1970. From Table 3. 4 and Figures 3. 3 and 3. 4 it can be seen that after May 1970 the major part of the Norwegian catch came from the north-western North Sea and west of the Shetlands. The considerable numbers of the 1967 year-class recaptured must have been derived from this area.

In the case of the returns which came from factories at Esbjerg, Skagen and Thyboron, it was possible, by using the available age composition data, to calculate the number of recaptures per 10 000 tags released, per 106 herring processed, of the 1967 and 1968 year-classes. These data are given in Tables 3. 7 and 3. 8. The data for Esbjerg show no systematic variation with time, suggesting that no change took place in the ratio between tagged and untagged fish.

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Figure 3. 4 Reported locations of fisheries by Danish, Norwegian and Scottish vessels (from ICES Statistical Newsletters and national sources). In accordance with the North-East Atlantic Fisheries Com -mission conservation recommendation there was no herring fishery in May 1971.

I ... "'

Table 3. 7 Number of recaptures per 10 000 tags released per 106 herring processed, Esbjerg

Recapture 1968 year-class 1967 year-class month

Experiments Numbers Experiments Numbers caught caught

8-10 11 15-17 18 27-29 X 10-6 2-5 19 20-23 X 10-6

--- - -- --- --- --- --- - -- --- -1969

August 9.96 55.07 September 0. 37 27.33 1.05 95.92 October 0. 58 1. 75 46.37 1. 75 38.06 November 0.11 0.11 December 0.21

1970 I

January 0.90 0.53 1.44 2.26 24.39 1. 85 3.24 ~

February 2.06 1. 35 3.34 2.70 130. 03 7.12 5.80 4.24 28.52 0)

March 1. 20 1.16 5.16 4.09 0.52 23.24 11. 22 15. 31 25. 51 0.98 April 2.86 1. 34 4.70 3.36 1.44 29.77 1. 90 1. 35 1. 62 11.14 May 2.08 1. 23 3.28 2.87 0.22 54. 34 2.19 2 . 34 2.10 12. 83 June July 2.81 1. 55 4.96 4.45 0.92 34. 86 4.12 5.62 4.12 2.67 August 1. 70 1. 53 3.41 2.54 1. 31 70.74 0.58 0.53 0.94 41. 39 September 1.47 1. 80 3.16 0.17 46.23 0.59 0.35 25.39 October 2. 91 0.99 4.05 4.97 0.61 13. 08 0. 76 0.69 0.76 11. 71 November 11. 36 22.73 11. 36 2.27 00.88 12.50 0.16 December 4.16 0.41

1971

January 0. 24 8. 39 1.18 February 0.54 0.71 1.19 2.17 0.43 18.43 5.93 1. 35 March 0.21 0.09 23.49 0.64 April 0.26 0.68 0.51 0.10 77.91 0.33 0.33 15.09 --

Total no. processed 633.64 559.94 559.94 559.94 405.52 345. 75 153.45 153.45 X 10-G

Recaptures 920 424 1 557 1 393 228 1 063 278 264

Table 3. 8 Number of recaptures per 10 000 tags released per 106 herring processed, Thyboron, 1968 year-class, and Skagen, 1967 year-class

Recapture Thyboron, 1968 year-class Skagen, 1967 year-class month

Experiments Numbers Experiments Numbers caught caught

8-10 11 15-17 18 27-29 X 10-B 1 7 X 10-6 - -- --- - -- --- --- -

1969

August 0. 38 14. 35 9.48 September 25. 00 1. 20 7. 30 14.60 9.11 October 24.87 8.82 5.67 24.79 12.40 1. 21 November 16. 33 30.61 0.49 December 217.65 311. 76 0.17

1970 I

January 27.59 0.29 ,i,.

February 3.10 40.00 14.55 0.55 -'I

March 0.35 0.42 April 0.17 59.46 0. 37 May 19.51 0.41 June 4. 32 4. 32 1. 85 July 11. 51 5.23 3.06 August 3.02 2.04 6.65 13.22 2.27 13.24 September 7 . 08 3.68 13.60 26.91 3.68 3.53 115. 38 61. 54 0.13 October 2.43 5. 83 12 . 14 2.06 November 0.19 December 4 . 55 1. 79 4 . 46 1.12

1971

January 0.52 February 1. 33 March 1. 22 April 0.98 --

Total no. processed 35.70 35.70 35.70 35.70 35.70 27.54 18.06 X 10-6

Recaptures 85 40 158 315 43 422 236

100

80

60

~

m 40 Q)

~

~ 20 a.

12110 0

519

- 48 -

418 •

619 •

318 •

(a)

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Thou so nds of fish processed per week

(b)

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Figure 3. 5

4 B 12 16 20 24 28 32

Hundreds of fish processed per week

The relation between tag returns per week from liberations 2-5 and numbers of fish processed at Esbjerg: (a) returns during first 11 weeks after liberation. Numbers

associated with each point refer to week number and month (August-October 1969);

(b) returns during January-March 1970.

- 49 -

3. 2 Analysis of returns from the fishery for juveniles

3. 2.1 The Petersen method for stock size estimation

As. a first approach the Pete sen method was used. Stock size in num­bers, "N', was calculated from"'N' = T(C/R), where T is the effective number of tagged fish, R the number of recaptures and C the corresponding catch, over the same time period, in numbers corrected for magnet efficiency. This will give the size of that year-class at the time of tagging. Only returns from the factories in Esbjerg and from the Norwegian factories were used in these estimates.

The estimates from Norwegian recaptures are based on returns in January and February 1970 only. The Norwegian fleet was then fishing in

the southern part of the central North Sea, just outside the Bliden area, and the percentage age composition was:

Year-class

1966 1967 1968

Percentage 2.0 80.6 17.4

The majority of tags recovered were from liberations comprising the 1967 year-class.

With the larger numbers of tags recovered per week at Esbjerg a more detailed analysis of the returns from each liberation was possible. The num­ber of returns per time unit were plotted against the corresponding catch, either in number or in weight. Examples are shown in Figures 3. 5a-e, and some cases call for special mention.

Figure 3. 5a shows the weekly recaptures at Esbjerg from liberations 2-5, plotted against the corresponding catch in tonnes. In order to correct for the delay of the tags in passing through the production lines, the catch is taken as 2/3 of that landed in a week plus 1/3 of that landed in the previous week. It is evident that the rate of recapture during the first 4 weeks (August 1969) is very different from that in the successive 8 weeks (September and October), and that a sharp change took place between weeks 4 and 5. This change becomes even more pronounced if the results of magnet tests are applied to the uncorrected catch and recapture data used in Figure 3. 5a. According to those tests, the overall magnet efficiency in Esbjerg was as low as 32 per cent in August 1969, due to installation of new machinery in two of the three factories; the efficiency rose to 7 5 per cent in September-October. A possible explanation of the features shown in Figure 3. 5a may be that the efficiency tests apply to different production lines in the two periods, and that the overall efficiency was not measured in either.

From the recaptures of the same group of liberations in the first three months of 1970 (Figure 3. 5b) and also from liberations in the 1968 year-class (Figures 3. 6a -c) it would appear that the suspected problem with magnet efficiencies has been reduced. The stock size of the 1967 year-class has therefore been calculated using the data for January to March 1970 (Table 3. 7).

I

0 ~

180r Esbjerg 1970 (a) /x r (b) Exp. 8-10 • Exp. 15-17 X 1 2 I Esbjerg 1970 Exp. 11

140 I /

.&::. 1 0 -10 0 I- /x ~ C 0 E ~ 8

.s::::. Q)

~ 60 Q.

0

E "CJ Q) 6 C

~ 20 ~

=> Q. .....

Q)

4.-0 20 40 60 80 100 120 140 ~ -/ • "CJ Q)

Cl) C: en ~ 80~ Esbjerg 1970 / C,

(c) 1-- 2 1» Exp. 18 ~

en 6 0 C7'I 0 0 0 20 40 60 80 100 120 t-

40 Millions of fish processed per month

20

0 0 20 40 60 80 100 120 140

Millions of fish processed per month

Figure 3. 6 The relation between tag returns per month and numbers of fish processed at Esbjerg: (a) returns from liberations 8-10 and 15-17; (b) returns from liberation 11; (c) returns from liberation 18.

140

- 51 -

Two important groups of tag releases for the 1968 year-class are shown in Figure 3. 6a, Each plot shows a reasonably constant rate between the num­ber of recaptures per month and the corresponding number of fish of that year-class processed. Despite the comparatively small difference in space and time between liberations 8-10 and 15-17, the latter group leads to a stock estimate which is only 53 per cent of that derived from the former. This could indicate that the calculated numbers of effective tags in one, or both, groups of experiments are erroneous, perhaps from the influence of environmental factors upon the tagging mortality rate and a higher mortality rate amongst the smallest fish. Stock sizes calculated for different experi­ments are shown in Table 3. 9

Table 3. 9 Stock sizes of the 1968 year-class - Esbjerg catches

Liberation Average size Bottom Total Stock number of fish tagged temperature recaptures size

(cm) (OC) per 10 000 fish tagged(l)

(10-9)

8 14.2 7.5 } 6.3 9 14.8 7.6 920 4. 7

10 15.3 12.0 3.1 11 15.2 14.0 592 7.3 15-17 16.5 11.7-13.4 1 562 2.9 18 17.4 9.8 1 398 3.4

1Total recaptures to April 1971 (Table 3. 6a).

There is some indication that the higher numbers of recaptures are associa­ted with larger fish being tagged in warmer water. Conversely the lower numbers of recaptures from liberations 8-11 result in the estimation of higher calculated stock sizes. However, the evidence is not explicit enough to apply a correction on this basis.

Stock size estimates are summarized in Table 3.10. Fishing mortali­ties were estimated by assuming that the stock size estimates refer to 1 January 1970 and then calculating F from:

C = N { F / (F + M)} { 1 - e -( F + M)} ,

where C is the total catch of that year-class in 1970. It was further assumed that M = 0. 1.

- 52 -

Table 3.10 Catches in number x 10-6, estimated stock sizes in number x 10-9, and mean fishing mortality from 1967 and 1968 year-classes - Petersen method

Year- Liberation Stock 1970 Mean Mean

class number catch(2) stock fishing Esbjerg(l) Norway mortality

1967 2- 5 2.4 3.1 19 2.3 0.922 2.65 0.45

20-23 2.8 Mean 2.65

1968 8-10 4. 9( 3)

11 8.6 1.146 4.0 0.36 15-17 2.8 18 3.0 Mean 4.83

1From weekly recaptures and fish processed in weight, January-March 1970. 2catch in Division IVb (Anon. 1972, Table 9). 3calculated by averaging data in Table 3. 7 for January-October 1970.

A basic assumption in the Petersen method is that the proportion of tagged fish in the catches, used to estimate N, is the same as in the rest of the population. Comment has already been made on differences in the pattern of returns of tagged herring from the liberations based on the 1968 year-class. Liberation 11 was made south of 55°30', but 8-10, 15-17 and 18 were made in the northern area. The differences in the estimates of the 1968 year-class may be explained by different behaviour of the tagged fish in the southern and northern parts of the area. If the tagged fish in the southern area migrated out of the main area fished, these experiments will give overestimates of the stock size. Similarly, if fish tagged in the northern area migrated into the main area fished and concentrated there, the northern experiments will under­estimate the stock size. Such under- and over-representation of tagged fish in the catch may result in a serious error in the estimates.

From the plots of the number of tag recoveries per time on the amount of catch processed it is evident that the Petersen method would be invalid in calculating stock sizes for some liberations. This is especially so in the case of the 1967 year-class, which was migrating out of the juvenile fishery in 1970. These liberations have not been included in Table 3.10.

Using the German biological samples to estimate the catch in numbers, the reported recaptures in January-April 1970 from the German factory with the highest production gives the estimates of stock size shown in Table 3. 11.

- 53 -

Table 3. 11 Stock size estimates, in millions, from German data

Tagging 1967 year-class 1968 year-class

Experiments Returns Stock Experiments Returns Stock

Skagerak 13 15 14 15

Northern 8-10 148 10 300

Bl¢'den 15-17 379 4 000 18 521 2 900

Southern 2- 5 43 8 800 11 148 10 300

Bl¢'den 19 38 9 900 27-29 13 117 800 20-23 19 19 900

The estimates for the 1967 year-class are much higher than those based on Danish and Norwegian recaptures. Those for the 1968 year-class, except that from liberations 27-29, are in general agreement with the estimates based on Danish recaptures. The return of tags from liberations 13 and 14 in the Skagerak by the German plant can be due to the processing of offal from fish imported to the Federal Republic of Germany. This highlights one of the uncertainties in the German material. Additionally, because of the uncer­tainties in the German catch figures referred to previously, one should not consider the stock estimates to be equally as good as the others.

The Norwegian recaptures in June-August 1970 were also used to esti­mate stock size. Almost all the catch in this period came from area IVa W (Shetland), and it is assumed that all the reported tags came from this area.

The estimated age composition of the catch for the whole year and all countrie8 in this area was used to estimate catch in numbers by age groups (Anon. 1972). Very few of the 1968 year-class were caught, and the relative precision of the estimate of numbers caught of this year-class is too low to make any estimate of stock size. The results for the 1967 year­class are shown in Table 3. 12.

Table 3.12 Stock size estimates, in millions, for the 1967 year-class, from Norwegian data

Tagging location Experiments Returns N

Southern Bl¢'den 2- 5 93 23 300 19 181 12 000 20-23 148 14 600

These estimates give considerably higher values than the others. Possible explanations could be that the tagged fish in the Bl¢'den area have not migra -ted to Shetland in the same proportion as the rest of the year-class, or that the Shetland stock of adult herring is not recruited from Bl¢'den alone.

- 54 -

3. 2. 2 Test of equal catchability of tagged fish

Methods of estimating the quantitative characteristics of an animal population which rely on catching individuals from the population require that the catchability of all individuals be the same. A test for equal catcha­bility has been proposed by Cormack (1966). Catchability, as defined by Cormack, is the probability with which an individual makes itself accessible to capture. The probability that it will be caught depends on its vulnerability and on the intensity of fishing.

Cormack's test assumes that the probability of an individual being caught on any occasion does not depend on how often the animal has been caught previously. The test requires that either the size of the entire popu -lation - or, more often, the size of some identifiable sub-population - be known. This known population is subjected to sampling on two occasions, individuals captured on the first occasion being marked and returned to the population. The number of individuals taken on the second occasion, the numbers of these which had also been taken on the first occasion and the total number taken then must be known.

In the present instance the population of known size has been taken to be the entire stock size, N, of the 1967 and 1968 year-classes at 1 January 1970, the total number being 7 475 x 106 (Table 3. 10). The number of these fish taken on the first occasion and effectively marked was 38 266 (total effective release in all liberations). The number of individuals subsequently removed (1970 catch) from this population was 2 068 x 106 (Table 3.10) and the number of recaptures by the end of 1970 was 5 215 (Table 3.1).

From these figures the following quantities may be calculated:

Ill 2 = number of fish seen on both occasions = 5 215 '

Ill = number of fish seen on first occasion, but not on second

= 38 266 - 5 215

= 33 051

n2 = number of fish seen on second occasion, but not on first

=- 2 068. 106 - 5 215

:::.., 3 199. 106

Under the assumption of equal catchability of all members of the population, the variance, or equivalently the coefficient of variation, of the distribution of catchabilities is zero. Cormack shows that this coefficient of variation is estimated by

with estimated variance

- 55 -

The estimated coefficient of variation may be assumed to be normally distri­buted with mean zero, under the hypothesis of equal catchability, and with variance given by the above. If the estimated coefficient of variation is nega­tive, as is the case here, the hypothesis of equal catchability is not rejected.

Table 3. 13 Total effort as hours fishing , Esbjerg

Single Pair Total: (2 x pair) + single

1969

August 9 368. 0 3 993. 5 17 355.0 September 8 608. 5 3 547. 5 15 703. 5 October 4 143. 6 2 815. 0 9 773. 6 November December

1970

January 1 645. 5 1 645. 5 February 9 646. 5 48.0 9 742. 5 March 9 212. 5 9 212. 5 April 8 562. 0 606.0 9 774. 0 May 4 578. 0 782.0 6 142. 0 June July 12 189. 0 3 288. 5 18 266. 0 August 13 318. 5 7 343. 8 28 006. 1

September 14 804. 5 5 077. 5 24 959. 5 October 8 939. 0 3 7 95. 5 16 530. 0 November 8 196. 5 103. 0 8 402. 5 December 4 567. 5 1 581. 5 7 7 30. 5

1971

January 11 069. 6 480.0 12 029. 6 February 18 800. 8 1 291. 0 21 382. 8 March 23 531. 7 2 108. 0 27747.7 April 26 426. 5 2 590. 0 31 606. 5

3. 2. 3 Nun:i.ber of recaptures per unit effort

The only series of comprehensive effort data is that from the Danish port of Esbjerg. Table 3.13 gives the total number of hours fished per month by industrial vessels which landed herring. Using these data and the numbers of tags per 10 000 liberated per million fish processed (Tables 3. 7 and 3. 8), the numbers of returns per unit effort have been derived (Table 3. 14). Regression of the logarithm of these recaptures per unit effort on time was made for the 1967 and 1968 year-classes, using data from Esbjerg. The time unit used was one month.

- 56 -

Table 3.14 Tags returned per unit effort x 1 o-6, Esbjerg

Recap~re 1967 year-class 1968 year-class month

Experiments Experiments

2-5 19 20-23 8-10 11 15-17 18 27-29 --

1970

January 1124 547 322 875 1 373 February 730 595 435 211 139 342 277 March 1 217 1 552 2 759 130 126 560 444 56 April 194 138 166 293 137 481 344 147 May 356 381 342 339 200 534 467 35 June July 225 308 226 154 85 272 244 50 August 20 19 34 61 55 122 91 47 September 23 14 59 72 127 7 October 46 40 46 176 60 245 301 37 November 3 December

1971

· January 20 February 277 25 33 56 101 20 March 8 3 April 10 10 8 22 16 3

For the different experiments the following values for the slope and intercept of the regression equations were obtained (Table 3. 15). The slope equals F + X, where X represents all apparent mortality other than that due to fishing (F), and is an estimate of the monthly total mortality (Z).

Table 3. 15 Regression parameters

Year- Experiments Slope Intercept class (F + X)

1967 2- 5 0.26 6.93 19 0.43 7.65 20-23 0.35 8.61

1968 8-10 0.24 6. 38 11 0.15 5.57 15-17 0.26 7.10 18 0.20 6. 84 27-29 0.23 5.25

- 57 -

Attempts to estimate the fishing mortality from the intercept,

gave no reasonable results, due to its large sampling variation.

3. 2. 4 Estimation of catcbability coefficient

The catch per unit effort in any time interval is proportional to the abundance at the beginning of that interval. The abundance at any time is a function of the product of the total effort expended up to that time and the catchability coefficient (q). The latter may be estimated from successive values of the catch per unit effort and the cumulative effort. This method, due to DeLury (in Ricker 1958), was used to estimate q from the data for Esbjerg given in Tables 3. 13 and 3. 14 over the period January 1970 to April 1971 inclusive. Months in which there was fishing effort but no tags were returned were omitted from the analysis, but the effort was included in the accumulated sum. The estimates of q and their standard errors, obtained by carrying out a linear regression analysis of ln tags per unit effort on cumulative effort (measured in units of thousand hours fishing), are given in Table 3.16. These values of q are based on the numbers of recaptures per 10 000 liberations. When expressed in terms of effective liberations, they must be multiplied by the factor

(effective number of liberations)/10 000.

The corrected catchability coefficients are also given in Table 3.16; their mean value is O. 0053.

Table 3.16 Estimates of the catchability coeffi­cient, q, from Esbjerg data

Experiments

2- 5 8-10

11 15-17 18

q

0.0169 0.0159 0.0110 0.0145 0.0136

Corrected q

0.0110 0.0063 0.0008 0.0058 0.0027

3. 3 Analysis of returns from the fisheries for adults

Earlier in this report comment has been made on the difficulty of referring recovered tags to the fishing areas. There are two main sources of error. Firstly, the tag may remain in the fish-meal plant for a consider­able period before detection. In magnet efficiency tests delays of over one month have been known. Secondly, when vessels make many shots in an area or when more than one major area is fished the allocation of a recovered tag to a statistical rectangle must be treated with some caution. In practice the allocation tends to be made to the area from which the greatest catch came.

6' 62'

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r 60'

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52'

51°

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60'

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59' 13

'58'

57°

55'

51.'

52"

51'

- 58 -

I.' 2' o· 2• I.' 6" 6' 10' 6' I.' 2' o· 2' I.' 6' 62°

r T T 7 > r T 7 r 7 l 6 35 7 \ 61' 6 55 2

+ +~f + + --l \ I- +~r, I- _J \ \ \ 64 11 2 60' 97 75 5

+ + ..L ..L _J 0 + q.~+ _J L _J 0 .. , k r k 38

~ 59' 113 ·35

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+ + _J a + + _j r --j Q

k r k .. , 3 59' 9

L _j

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56'

55'

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SJ'

52'

51°

Figure 3. 7 Number of tags recovered in Norwegian and Scottish fisheries, referred to approximate areas of recapture.

6' 10'

6' 10'

'"CJ a, L­:::, ....., 0.. d u a, L-

- 59 -

Because of the nature of the Scottish and Norwegian fisheries it was possible for the national reporting agencies to refer most of the recovered tags to either rectangles or rather broader areas. From a knowledge of the monthly distribution of the fisheries the recaptures made by Norway and Scotland have been combined in units of four statistical rectangles, and the annual totals are shown in Figures 3. 7a-d.

The recovery of tags from areas to the west of Orkney and Shetland is a notable feature in all years. From the returns from the Scottish plants it has been possible in some cases to identify tags which could only have been caught in the area of the North Minch. Although this has clearly demonstrated that the south-eastern North Sea is a nursery area for fish which may subsequently recruit to the areas west of Shetland, it is not possible to estimate either the proportion of these fish in the nursery area or the proportion of those fish originating from the North Sea nursery ground in the total stock in Region VIa. The difficulties arise from the uncertainty in area of recapture of the tagged fish and the absence of any biological data on those fish when captured. An analysis of the racial characters of the fish sampled during the tagging is to be carried out and will be reported at a later date.

Total mortality estimates on the 1967 and 1968 year-classes may be obtained from the regression of the logarithm of the numbers of tags recovered in time t against time t. From Table 3. 1 the tag returns have been grouped by six-month periods from July 1970, and the regressions are shown in Figures 3. 8a and b. Under the assumptions that the mortality and the proportion of tags that are reported each year are constant, then the slope gives an estimate of apparent total mortality over the period 1971-73. Assuming a natural mortality of 0. 1, as has been used by the ICES Herring Assessment Working Group, these estimates compare well with the fishing mortality of 1. 09 for all fish older than 1-ring in 1971 (Anon. 1974, Table 2. 9). If, however, tagged fish emigrated from the exploited area or the rate of reportage decreased in the later years the apparent fishing mortality would be an overestimate.

700 ( Q) 700. ( b) '"CJ a,

• • •

L-:::,

Z = 1-12 +-' 0.. d

Z = 1-09 u a, • ....

~100 en 100 01 • d ...... -0

E :::, en

•

1957 year- class

10 ,_____,__--r-.._____._--.-...,_____. ____ • _J

1970 71 72 73

d +-' -0

E :::, en

C: 1958 year - class ~

10 ,____,..--,.._...,________._...,__~ • ___J

70 71 72 73 Figure 3.8 Logarithms of numbers of tags recaptured per 6-month period from

July 1970.

- 60 -

4 The model

At its meeting in September 1971 the Group was informed that a general computer program of a dispersion model was currently being developed at the Danish Fishery Laboratory by Mr Hans Lassen, and it was decided that a modified version of this program, suitable for handling the present material, should be written and applied. This task was undertaken by Mr M. Nicholson (Marine Laboratory, Aberdeen), using the large computer facilities available at the Scottish Office Computer Centre (Edinburgh) and at the North European University Computer Centre (Denmark). The model developed is described in detail in Appendix IX.

Briefly, the computer model consisted of a set of equations relating fishing effort and fish distribution to the number of tags returned in succes­sive equal time intervals, each of four weeks. A regular-shaped grid of equal-sized squares was required for the model, and a grid comprising 27 statistical rectangles was found to give a reasonable approximation to the Bl~den area (Figure 4. 1). The movement of the tagged fish across this grid was simulated, and using the distribution of fishing effort in these statistical rectangles, a series of predicted tag returns was constructed. This series depended on the values given to the parameters in the mathematical specifi­cation of the model, namely:

(i) migration and dispersion parameters,

(ii) instantaneous natural mortality coefficient,

(iii) catchability coefficient.

Besides allowing fish to move within the Bls6den area, fish were allowed to leave it, and three types of emigration from the area were considered. With reference to Figure 4. 1 these were:

(a) no emigration at all,

(b) emigration through the northern, western and southern exits, and

(c) as in (b) plus emigration through the Dogger exit.

All other boundaries were totally reflecting.

Separate computer programs were written for each of these emigration types. Various combinations of different values of the model's parameters were used in each program, and in this way a large number of possibilities was simulated.

The predicted tag returns generated by these computer programs were plotted against time and compared with plots of the observed returns. From these comparisons, it was possible to identify the type of emigration and the set of parameter values giving the best fit to the observed data.

The data used were the numbers of fish effectively liberated (Table 2. 8), the effort per four-week period in each of the 27 statistical rectangles, and the corresponding tag returns in each time period. Tag returns and fishing effort were restricted to data from Esbjerg, Denmark's major port.

A 8

Figure 4.1

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C D E F G H K L M N

Exit North 1 2

11

~\ 1 0 ~ ~~,:::,;

9 . '\. <,_,4r-'

Blia den Fishery

6

5

I.

3

2

The area of the Bl0den fishery as defined in the simulation model.

The fishing effort used in this analysis, aggregated over the 27 statis­tical rectangles for each time interval, is given in hours fishing in Table 4. 1. These data were based on sampled effort at Esbjerg and have not been raised to total effort. Also, the data refer to single and pair herring trawls, and will not correspond to the effort given in Table 3. 13, which refers to all vessels landing herring at Esbjerg.

Because of the impossibility of relating the return of tags to any parti­cular fishing area for the Esbjerg fleet, it has been assumed that all tags were recaptured within the 27 squares defined as the Bl0den. In the main, this assumption can be justified by reference to Figures 3. 1-3. 4. Almost 90 per cent of the Esbjerg herring trawl effort in 1970 was concentrated within these 27 statistical rectangles.

Three groups of liberations were analysed separately. A summary of these (abstracted from Table 2. 8) is shown in Table 4. 2, and the position of release on the Bl(b'den "grid" is shown in Figure 4. 1.

Table 4.1

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Hours fishing aggregated over the 27 statistical rec­tangles of the Bl95'den for each four-week time interval

Time interval Month Effort

1 July /August 1969 6 049. 5

2 August/September 1969 4 845. 0

3 September /October 1969 3 094. 0

4 October/November 1969 80.0

5 November /December 1969 256.0

6 December/January 1969-70 415 . 5

7 January 1970 7 168. 5

8 February 1970 4 819. 0

9 March 1970 6 149. 0

10 March/April 1970 5 889 . 5

11 April/May 197 0 546.0

12 May /June 1970 91. 5

13 June/July 1970 10 724. 0

14 July/August 1970 11848.8

· 15 August/September 197 0 7 050. 0

16 September /October 197 0 4 615. 0

17 October/November 1970 86.0

18 November/December 1970 968.5

19 December 1970 3 076. 0

Table 4. 2 Grouping of liberations

Liberation Date of Number of Year-number liberation liberations class

2- 5 July/ August 1969 6 539 1967 15-17 October 1969 3 990 1968 20-23 January 1970 4 388 1967

7

6

5

\ \ 4 \

3 ' 2

en 1

' ' ' ' \

Experiments 2. 3,4. and 5

\ V

Observed tags Predicted tags

en C,

01 I _/ ~-- -- -o ~ I I - -I ' I I - I I t

en ""'C

Cl,J L... -c C:

Experiments 15, 16, and 17 ~3

2

1 ....

O' I I -- = ----------, I I I I :::::...·,.,.....--: I I I ,

July Aug Sept Oct Nov Dec Jan Feb Mar Apr May Jun July Aug Sept 1969 Time Interval 19 70

Figure 4. 2 Comparisonof the predicted and observed 4-weeklytagreturnsat Esbjergfor liberations2-5 (1967 year-class) and liberations 15-17 (1968 year-class). As the time intervals run from the date of tagging, the 4-weekly periods are also shown approximated to calendar months.

I O')

w

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Values of the natural mortality coefficient varying between 0. 1 and 0. 25 were tried in the model, but from the early computer runs it became apparent that within these limits the model was relatively insensitive to the value given to natural mortality. Because of this, and to reduce the number of variable parameters in the model, the value of natural mortality was set at 0. 2 for the remaining computer runs. Of the three types of emigration which were con­sidered, that which allowed fish to pass through all four exits gave the best results, although the differences between the three sets of results were not large. For the group of liberations 2, 3, 4 and 5, the predicted returns obtained by simulating migration to the north-east fitted the observed returns better than those obtained by simulating migration in any other direction (Figure 4. 2). The best value of the catchability coefficient (relative to hours fishing per statistical rectangle per time interval) was found to be q = 0. 0025.

The best direction of simulated migration was to the south-west (Figure 4. 2) for the group of liberations 15, 16 and 17 and the optimal value for the catchability coefficient was also q = 0. 0025, agreeing with the result from the previous group of experiments.

All attempted sets of parameter values predicted tag returns in much greater numbers than those observed for the group of liberations 20, 21, 22 and 23. However, these releases were made in January 1970 and consisted of the 1967 year-class. It is thought that these fish would have left the Bliden area almost immediately after release; this would explain the failure of the model when applied to this group of liberations. Taking the value of q obtained from both series of liberations 2-5 and 15-17, and using the relation­ship

27 F. = q x I; f .. / 27 ,

J i=l lJ

where fij = hours fishing in the ith statistical rectangle and jth time period, then using the data in Table 4.1 a coefficient of fishing mortality, Fj for the jth time period may be calculated. Fishing mortality coefficients calculated in this way are given in Table 4. 3. They cover the period from July 1969 to December 1970, and are expressed relative to a four-week time interval. An average annual F for 1970, given by

F ::: 19 I;

j=7 F. I

J

has the value F O. 45. This estimate of fishing mortality is in close agree­ment with those obtained from the Petersen and cohort analyses.

Using this value of F, the natural mortality coefficient of 0. 2, and the juvenile catch in 1970 it has been calculated that 33.1 per cent of the stock would have been taken during 1970. This percentage has been calculated using

the catch relationship

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where Ct is the catch in number over period t,

Pt is the stock in number at the beginning of period t,

Ft is the fishing mortality coefficient in period t, and

Mt is the natural mortality coefficient.

The catchability coefficient obtained from the model was q '" 0. 0025. In order to compare this catchability coefficient with the values obtained in Section 3. 3 it must first be expressed in equivalent units. The effort data used were based on a sample of 76 per cent of the total Esbjerg data, and to give q a value relative to 1 OUO hours fishing per annum for the whole fishery, we require a conversion factor given by: 0. 76 x (1 000/13 x 27) = 2.165. This gives a value of q of 0. 0025 x 2.165 == 0. 0054. This value of q (for

experiments 2-5 and 15-17) compares favourably with the results in Table 3. 16 •

Although the model had no facility for estimating the direction of migration directly, the differences obtained by varying the simulated direc -tions of migration were so pronounced that the north-east migration for liberations 2-5 an<l the south-west migration for liberations 15-17 were unmistakable.

These results are supported by the patterns of tag returns observed in Section 3, as are the results from liberations 20-23, for which the fish were considered to be leaving the Bl!6den area almost immediately.

Table 4. 3 Fishing mortality coefficients for the jth time interval

Time Month Fj interval, j

1 July/ August 1969 0.043 2 August/September 1969 0.035 3 September/October 1969 0.022 4 October/November 1969 0.001 5 November/December 1969 0.002 6 December/January 1!)69-70 0.003 7 January 1970 0.051 8 February 197 0 0.034 9 March 1970 0.044

10 March/ April 1970 0.042 11 April/May 1970 0.004 12 May/June 1970 0.001 13 June/July 1970 0.076 14 July/ August 1970 0.084 15 August/September 197 0 0.050 16 September/October 1970 0.033 17 October/November 1970 0.001 18 November/December 1970 0.007 19 December 1970 0.022

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5 Discussion

In plam1ing the present tagging experiment it was natural to regard the young herring taggings in 1957-58 as a pilot experiment (Aasen et al. 1961). The shortcomings of the latter derived from:

1 inadequate catch and effort statistics for detailed distribution in time and space;

2 too few fish liberated (about 2 700) at too few localities;

3 too few factories with effective installations for recovery of tags;

4 no direct attempt to assess initial tagging mortality;

5 insufficient biological sampling of the tagged population and of the commercial fisheries;

6 too many different tagging teams to ensure a reasonably uniform handling of the tagging operations throughout the period.

As a consequence of these deficiencies the analysis of the comparatively low number of tag returns was difficult.

In the present experiments the necessary increase in the number of tagged fish and of tagging positions was achieved by extending the period from one month to eight months and by releasing 30 per cent more fish per station. Even so, the number achieved fell far below the intended target of 100 000.

The need for experimental work on tagging mortalities was met with and facilitated by the presence of large tanks on board the hired tagging ves­sel. More uniform handling of the fish was obtained by the deployment of the same two tagging teams throughout the entire experiment. By estimating tagging mortality, and by the use of the same taggers throughout, it was hoped that the losses due to handling would not vary too greatly between experiments. Nevertheless, it has become clear from the subsequent history of the tag returns that this may not have been achieved in all cases. Consis­tently low levels of tag returns, both as juveniles and as adults, have been obtained in a number of experiments. The apparent low numbers of effective tags released may be related not only to handling but also to environmental conditions in the area of release. It is not possible to make either a choice of explanations or a correction to the effective liberations. Using these experiments, absurdly high stock levels are derived from Petersen calculations.

Although improvements in the work at sea also included sampling each haul, it proved difficult to obtain clear improvements of the equally vital activities ashore. In working up the new data, difficulties were again met in the same categories of the commercial fishery data sampling and the magnet efficiencies. Serious doubts have been expressed concerning the level of tag reportage in September and October 1969. It is unfortunate that this criti­cally affects the interpretation of the data on the 1967 year-class. After January 1970 this year-class was rapidly withdrawing from the eastern nur­sery area and thus the estimates of stock size and mortality are likely to be biased.

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Judging from the biological samples taken at the time of tagging, some experiments were virtually conducted on single year-classes. It is unlikely that many fish other than those of the 1967 and 1968 year-classes were tagged. The 1967 year-class entered the adult fisheries in early summer 1970. From liberations of this year-class tags were recovered from July 1969 until spring 1971 in the young herring fisheries. After that they occurred with increasing rates in fisheries over deep water and even to the north of Scotland. In con­trast, the 1969 year-class was 0-group when the taggings began in 1969 and there are indications that this year-class remained in the eastern North Sea throughout 1970. In 1971 this year-class showed the same drop in abundance as did the 1967 year-class one year earlier.

In view of the differences in the 1967 and 1968 year-classes mentioned above, the recaptures from them must be considered separately. In conse­quence, the lack of relevant age data has resulted in material of some ports and countries being left out of the analysis. In effect, this means that the main analysis was again dependent on the data from Esbjerg.

A number of methods for analysing tagging data were tried. The Petersen method and the model utilize somewhat different sets of data and the results obtained are independent. This difference in data within the Esbjerg material arises from the choice of material for the model. In both series the total number of tags recovered in Esbjerg are used, for which no information is available on area of capture. These data are used also with estimates of the total numbers of the year-class processed in Esbjerg for the Petersen method, irrespective of location of catch.

For the model a selection of 27 squares was made and also a fleet of specified vessels using partkular gears. The total effort for these vessels and squares js different from that for the total Esbjergfleet as reported in ICES Statistical Newsletters, and the two series are not comparable. Assuming all tags to have been returned from within the 27 squares, the model sought to reproduce the monthly pattern of tag returns from these effort data. This was more successful for the 1968 year-class than for that of 1967.

Table G. 1 shows the fishing mortalities derived by these two methods and, for comparison, the value from the cohort analysis reported by the North Sea As1;essment Working Group. Because in 1970 the main weight of the Esbjerg t1eet was directed at the 1968 year-class, the fishing mortality reflects the exploitation of this year-class by the industrial fleet. It is seen

that these three e stimates are very similar, but the 1967 year-class value from the Petersen method and the model are very different from that of the cohort. The cohort fishing mortality is based in part on the subsequent his­tory of the stock in the adul i North Sea fishery, and a considerable part of these fish as 2-ringers are caught in the adult fisheries in the north-western North Sea in 1970. This fishing mortality is only in part a reflection of the exploitation on the Bl0den, whereas that derived by the Petersen method can be ascribed to the total juvenile fishery in IVb on this year-class.

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Table 5.1 Stocks at time of tagging and fishing mortalities in 1970

Method of Area Stock, x 109 Fishing analysis mortality (F)

1967 1968 1967 1968 --

Petersen Statistical div. IVb 2.7 4.2 0.45 0.33

Model " 2.7 3. 3 0,45

Cohort North Sea 3.2 3.4 1.08 0.46

It is concluded from this analysis that the fishery for juvenile herring removed about 34 per cent of the stock (in number) of the 1968 year-class as 1-ringers in 1970. As the 1967 year-class may be regarded as a by-catch, it is concluded that a similar proportion is removed of that part of the year­class remaining in the area of the fishery.

Stock size estimates are also presented in Table 5. 1. The Petersen and model estimates are referred to the total catches in IVb. The 1968 year­class Petersen estimate is somewhat higher than that from the cohort and model, but the 1967 year-class is somewhat higher in the cohort.

In the case of the 1967 year-class, 1 903 tags were recovered up to May 1970, after which this year-class left the Bl(i{den fishery. Between this date and February 1974 a further 1 028 tags were recovered from the adult fisheries. · Some of the recoveries were from west of Shetland and into the Minch.

In the case of the 1968 year-class, 2 352 tags were taken up to December 1971, when the fish were no longer represented in the Bl~den age data. Sub­sequently, a further 193 tags have been recovered, again mostly from the north and west of Shetland.

Recently, other evidence that recruits from the area west of Shetland occur in the North Sea juvenile fisheries has been presented (Anon. 1974). There is also evidence from these tagging data of a speedy with-drawal of the maturing herring from the North Sea to the Shetlands between March and June. The estimate of stocks of 0- and I-group in the North Sea would thus be somewhat inflated in relation to the cohort estimate, which reflects the adult North Sea stock as well. As the ratio of recruitment levels in area VIa to that in IV is of the order of 1:8 little more than the differences in the stock estimates observed could be expected if the whole of the recruit herring for VIa were present in the North Sea, and this is known to be a false premise.

Differential movement of tagged fish within the Bl(i{den area could not be examined directly because of the nature of the fishery and the difficulty of allocation of tags recovered to fishing area, although the model provided indirect evidence of movement. Two experiments, however, indicated that some tagged herring did not move into the areas exploited by part of the industrial fleet. It was not possible to follow up these observations from the point of view of racial composition of the tagged fish, due to the sampling coverage from the commercial fisheries.

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The considerable numbers of tags recovered in 1971, 1972 and 1973 from the adult fisheries have allowed an estimate to be made of the total mortality generated by these over the period 1970-73. Treating the two year-classes separately, the total mortalities were:

Period

1970-7 3

1971-73

Year­class

1967

1968

Total mortality

1.09

1.12

In the previous Bliden tagging experiment the rate of exploitation on I-ringers was 16. 9 per cent in 1957 and 18. 5 per cent in 1958. The present estimate of exploitation of I -ringers in 1970 is 34 per cent.

6 References

Aasen, 0., et al., 1961. ICES Herring Tagging Experiments in 1957 and 1958. Rapp. P. -v. Reun. Cons. int. Explor. Mer, 152: 50 pp.

Anon., 1971. ICES Working Group on the Blf/S'den Tagging Experiment. Report on the meeting at Charlottenlund, 29 March to 2 April 1971. ICES C. M. 1971/H: 3, 5 pp. (mimeo).

Anon., 1972. Report on the North Sea Herring Assessment Working Group, Charlottenlund Slot, 13-22 June 1972. ICES C. M. 1972/H:13, 61 pp. , Append. (mimco).

Anon., 1974. Report of the Herring Assessment Working Group for the area south of 62° north. ICES C. M. 1974/H:4 (mimeo).

Becker, G., 1969. Hydrographic conditions in the northern and central North Sea in the summer of 1969. Annls biol., Copenh., 26: 45-8.

Cormack, R. M., 1966. A test for equal catchability . Biometrics, 22: 330-42.

ICES, 1962. Mean monthly temperature and salinity of the surface layer of the North Sea and adjacent waters from 1905 to 1954. ICES, Service Hydrographique, Charlottenlund Slot, Denmark.

Ricker, W. E., 1958. Handbook of computations for biological statistics of fish populations. Bull. Fish. Res. Bd Can., (119): 300 pp.

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APPENDIX I History of the Bl¢den Tagging Experiment

In 1966 the North-East Atlantic Fisheries Commission posed a number of questions to be answered by the Liaison Committee in relation to the decline of the Downs herring stock. They were:

1 Whether

(a) a ban on herring fishing in the Sandettie area for one month each year (November);

(b) a stoppage of the Bl¢den herring fishery for one month each year (October)

adopted either separately or together could be expected to yield demon­strable benefit to the stock?

2 How long the above measures would have to be continued before these benefits became apparent?

3 What would be the effects on catches (both immediate and long-term) of these measures?

4 Whether they can recommend other experiments aimed at bringing benefits to the Downs stock, giving in each case the length of the time that the experiment would have to continue and the expected effect on catches both immediate and long term?

5 Whether they can recommend additional research that would assist in elucidating the cause of the decline of this stock?

The Liaison Committee in its reply recommended prohibition of herring fish­ing in the Southern Bight from October to March for at least 6-9 years, and stabilization of the Bl(i{den catch. In relation to Question 5, as more precise knowledge was needed on racial composition and fishing mortality in the Bl¢den fishery, the Committee proposed (ICES 1967) that:

(a) the International Tagging Experiment be repeated at the level of 100 000 taggings,

(b) samples be taken in association for racial analysis, and

(c) detailed catch and effort statistics be obtained from the fishery (Anon 1967).

At the 5th Annual Meeting of the North-East Atlantic Fisheries Com­mission in 1967 the following Resolution was agreed:

"The Commission

Having considered the report of the Liaison Committee on mea­sures that might be taken with respect to the herring in the Southern North Sea, and taking into account the concern expres­sed by some countries about the state of the herring stocks in the Central and Northern North Sea,

(i) stresses the importance of continuing investigations which may throw further light on the decline of the herring stocks spawningin the Southern North Sea, including larval surveys;

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(ii) endorses the recommendation of the Liaison Committee that a further substantial international tagging experiment should be undertaken on the Bliden ground, with supporting biological studies, including sampling for racial analysis;

(iii) urges the member countries concerned to cooperate in such an experiment to the maximum extent and in particular, in view of the importance of a better understanding of the effects of the Bliden fishery, requests that more detailed statistics of catch and fishing effort be made available from the fisheries for young herring;

(iv) asks ICES to formulate a programme of further research that would identify the factors affecting the stock of herring in the Central North Sea;

(v) invites the member countries concerned to intensify research on the herring stocks of the Northern North Sea, with special regard to data on fishing effort."

At the 1967 Statutory Meeting of ICES an ad hoc Group of the Pelagic Fish (Northern) Committee met under the chairmanship of Professor G. Hempel to prepare the plans and the cost of the proposed Experiment, taking into consideration the Commission's Resolution. The Report of this Group was studied by the Consultative Committee, who modified the proposals. Their recommendations, which were circulated to Contracting Parties on 8 December 1967, were as follows:

"Recommendations of the ICES Consultative Committee on Research on the Herring in the Bl0'den Fishery:

1 In its report to NEAFC in May 1967, the Liaison Committee referred to the small scale of the l 9:57 /58 International Tagging Experiment on the Bliden Fishery and, in order to provide up-to­date estimates of fishing mortalities in the various months and sub-areas of that fishery, proposed that the experiment should be repeated, at the level of 100 000 taggings (i.e. about 10 times the earlier annual scale), with associated research.

2 In its conclusions the Commission endorsed this proposal and urged member countries concerned to cooperate in the experi­ment to the maximum extent

3 Accordingly, the Liaison Committee requested the Pelagic Fish (Northern) Committee to consider the proposal further and indi­cate what would be the minimal requirements and what costs would be involved. The Committee appointed an ad hoc Group to advise on this. Its proposals were considered in great detail by the Consultative Committee. which recognized that although the most detailed scheme might well prove desirable, at the same time any proposal must be as economical as possible. On the other hand, the Commitice had also to take into consideration that certain reductions in expense could only be made at the cost of efficiency and reliability in the scientific results.

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4 Accordingly, the Consultative Committee recommends that in the first place an experiment operating over 8 months during one year should be undertaken, if the interested countries should approve, at an overall cost of 1116 000 D.Kr. (ship hire, D.Kr. 900 000; personnel, D.Kr. 126 000; miscellaneous, D.Kr. 140 000). It has to be recognized that, in the light of the results of the first 8 months, it may be necessary to repeat the experiment in a subse­quent year for 8 or even 12 months at a similar cost. For comparison the 1957 /58 experiment, operating for only two months in the first year, but repeated for a second year, cost in all between D.Kr. 250 000 and 300 000.

5 Allowing for the considerable increase in costs during the last 10 years, and the agreed need to increase the tagging rate 10-fold, the estimates seem to the Consultative Committee to be reasonable.

6 If, as the Commission would seem to wish, it is desired that this experiment be begun in 1968 (say, in August), then it will be essen­tial to begin making arrangements soon, by authorizing the Chairman of the Liaison Committee, in conjunction with the President and the General Secretary, to establish an organizing group, under a named Convener. This group would need to meet not later than in January 1968, at national expenses, to make arrangements for operations to begin in August 1968.

7 Accordingly, the Consultative Committee requested the Bureau to ascertain the views of_ delegations in this matter and, if these are favourable, to seek a suitable financial arrangement, so that the programme can proceed as requested by the Commission and as proposed by the Consultative Committee. It is suggested that the possible need for, and arrangements for, a second year's experi­ment might be considered at a later ICES Meeting.

8 Lastly, the Committee requests that all the countries concerned be strongly urged to supply as quickly as possible complete data on catch, effort and stock analysis data, broken down by the smallest possible units of area and time. It must be stressed that this information is absolutely essential. If it is not collected nationally on a routine basis, it must in any case be provided for the duration of the experiments. "

The Liaison Committee's 1968 Report to the Commission discussed the proposed tagging experiment further:

"This experiment could provide a minimum estimate of the proportion of the juvenile herring stock in the Blr6den area taken by the fishery there. It is also aimed at elucidating the relative importance of the Blr6den nursery area in providing recruits for the Northern North Sea herring stocks. It should also provide additional information on the distribution and migration pattern of the juvenile herring both within and away from the Blr6den area. It must be emphasized that detailed catch and fishing effort statistics for the Blr6den fishery, broken down into units of area and time, and associated racial data, are essential for the analyses of the recaptures following the experiment.

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The timing of the experiment depends largely on the time it will take for countries . interested in it to provide the necessary financial support. Once this has been obtained, the preparatory planning group will require about 6 months to one year before the experiment can start. On the basis of replies received from countries so far it seems clear that the experiment cannot be started in 1968. " (ICES 1968).

Following further discussion in the Commission the President and General Secretary of ICES circulated a further Memorandum on the proposed experiment on 8 July 1968, which sets out in greater detail the objects of the experiments and the organization required to achieve these (see Appendix II).

In view of the response to this letter at the 1968 Statutory Meeting of ICES the Working Group on the Blr&den Tagging Experiment was set up, with Dr J. J. Zijlstra as Convener. This Working Group was to be responsible for the scientific planning, execution and final analysis of the material. In addition, an administrative Managing Committee for the Blio'den Tagging Experiment was set up to deal with financial problems related to the Experi­ment. Mr Hans Tambs-Lyche was a member of both Groups and so acted as liaison officer. The Working Group met in January 1969 to draw up detailed plans (Appendix III).

The Management Committee met in March and approved the programme and the arrangements being made to charter the purse seiner. The charter commenced on 15 July 1969, with Mr J. Sangolt as Supervisor. A copy of his instructions, drawn up by the Working Group, appears as Appendix IV. During the experiment a number of meetings of the Working Group have taken place. The composition of the Group has changed from those originally nominated to the first planning group. The attendance at the various meetings is summarized in Appendix V.

The difficulties in attempting to separate juvenile herring into potential recruits to the spawning stocks were such that, at an early stage, this racial investigation was excluded from the work of the Working Group. As such an attempted separation (ICES 1969) could only be conducted after the herring had recruited to the spawning fisheries, it was considered that any report should not be delayed by the problems arising from this analysis. Dependent upon the quality of the data on the racial characters from the spawning fisheries an analysis will be made outside the budget of the Blio'den Tagging Experiment.

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APPENDIX II Memorandum on the Bl¢'den Tagging Experiment from the President and General Secretary of ICES

(i) Terms of reference

In relation to the assessment of the causes of the decline in the southern North Sea herring fishery and the possible effect on it of the Bl¢'den fishery on juvenile herring, the Liaison Committee of ICES proposed in its 1 967 Report to NEAFC that a further international tagging experiment should be carried out on Bl¢'den herring, on a larger scale than those previously conducted in 1957 and 1958. It was now considered that the composition of the stocks fished in the Bl(&'den area, and the nature of the fishery there, have changed substantially from that time, and that therefore new, up-to-date estimates of the mortality rate generated by the fishery are required. It was considered further that the experiment should cover the spring as well as the autumn fishery in the Bl¢'den area, between which it is known that there are changes in the composition of the exploited herring stock.

At its fifth meeting in May 1967, NEAFC endorsed this proposal and urged member countries concerned to cooperate in such an experiment. At the request cf the Liaison Committee plans for the experiment, including minimum requirements and costs involved, were drawn up at the ICES meet­ing in October 1967, and were approved by the Council. A summary of the plans, which included a specification of the costs involved, was circulated by ICES to the member countries for their consideration. Some countries, how­ever, expressed their wish to have a fuller account of the plans before they could decide to take part in the experiment. This Memorandum is intended to serve this purpose.

(ii) Objectives of the experiment

(a) As in the 1957 /58 Bl0den tagging experiments, the main objective of the new experiment will be to obtain a minimum estimate of the pro­portion of the juvenile herring stock in the Bl0den area taken by the fishery there. This estimate is required to assess the effect of the Bl0den fishery on recruitment to the total adult herring population in the North Sea. Further, provided that adequate sampling for racial analysis is conducted, it is hoped also to obtain estimates of its effect on recruitment to each of the main spawning stocks separately.

(b) In addition, the new experiment should provide valuable information on the distribution and migration pattern of the juvenile herring within and away from the Bl0den area.

(iii) The experiment

1 Period Considering that the fishery for immature herring takes place continuously between August and April, and that during this period fish migrate continuously to and from the fishing area, the tagging period should cover the whole fishing season of 8 months. The results of the 1957 /58 joint tagging effort have been questioned mainly because of its restriction in time: the tagging took place in August only.

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2 Area The experiment should be aimed at covering the total fish-ing area as completely as possible. This area, which shifts somewhat from year to year and from month to month, can be roughly defined as situated between latitudes 54 and 57°N and east of longitude 1 °E.

3 Vessel From earlier experience it is known that only herring caught by a purse seiner are sufficiently viable for tagging. It is there­fore proposed to hire a purse seiner with its gear for the duration of the experiment, to ensure a supply of herring in good condition.

4 Tags Tagging should be carried out mainly with internal tags, aiming at a total of 100 000 tagged fish. Since internal tags can only be recovered in reduction plants, countries where such factories are in operation, and which reduce significant quantities of North Sea herring, juvenile or adult, will be requested to check the efficiency of the magnets in their plants.

Additional taggings with external tags will also be made on a smaller scale for recovery in the human consumption fisheries for adult herring. These will provide information of particular relevance to objective (b) specified above.

Experiments to determine the rates of tagging mortality and tag shedding should be carried out during the course of the experiment, both at sea in keep nets and ashore in tanks.

5 Personnel There are two types of work involved in the experiment:

(a) Scientific planning, analysing the data and reporting, which should be carried out by scientists of countries taking part in the experiment.

(b) The actual tagging work at sea This will require a tagging team of three, consisting of a supervisor and two assistants. It is recommended that a team of three people should be hired to do this work for the duration of the experiment, in order to ensure uni -formity and maximum efficiency in the tagging method throughout. In the earlier experiments in 1957 /58, when members of the vari­ous fishery laboratories in the participating countries carried out the tagging in turn, the frequent shifts in personnel were felt as a definite disadvantage.

6 Additional research It is an essential requirement for the experi-ment that detailed catch and effort statistics are collected from the Bl¢'den fishery during the tagging season, by the countries participating in the fishery for juvenile herring.

In order to trace the fish to the adult stocks, adequate statistics on catch and effort of the fisheries on adult herring are also urgently needed, not only at the time of the experiment, but also thereafter for some years.

Sampling for racial characters, for evaluating the effect of the Bl¢'den fishery in the separate spawning components of the North Sea herring population, should be carried out on both the adult and juvenile

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herring (of the same year-classes) in the countries in which the fish are landed.

The operation of the purse seiner during the experiment would be facilitated by the support from national research vessels. scouting for herring.

7 Costs The estimated costs of the experiment were specified in the letter of 8 December 1967 from the President and the General Secretary of ICES to Contracting Parties, with enclosure, and are repeated here for eas:v reference:

Ship hire ................... .. . . Personnel ................. . ... . Miscellaneous (tags, rewards,

meetings, etc. ) ............. . Contingencies (unforeseen) . . . ... .

D.Kr. ---900 000 126 000

140 000 84 000

Total D.Kr. 1 250 000

It is recognized that, in the light of the results of the first 8 months, it may be necessary to repeat the experiment in a subse­quent year for 8 or even 12 months at a similar cost.

For comparison, the 1957 /58 experiment, operating for only two months in the first year, but repeated for a second year, cost in all between D. Kr. 2 50 000 and 300 000.

Charlottenlund, 8 July 1968.

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APPENDIX III Report of the Working Group on the Bl!ll'den Tagging Experiment, 20-22 January 1969

(i) The Working Group considers as its terms of reference the following paragraph from the Memorandum on the Bl!li'den Tagging Experiment, dated 8 July 1968:

"In relation to the assessment of the causes of the decline in the southern North Sea herring fishery and the possible effect of the Bl0den fishery on juvenile herring on it, the Liaison Committee of ICES proposed in its 1967 Report to NEAFC that a further international tagging experiment should be carried out on Bl0den herring, on a larger scale than those previously conducted in 1957 and 1958 . It was considered now that the composition of the stocks fished in the Bl0den area, and the nature of the fishery there have changed substantially from that time, and that there­fore new, up-to-date estimates of the mortality rate generated by the fishery are required. It was considered further that the experiment should cove r the spring as well as the autumn fishery in the Bl!li'den area, between which it is known that there are changes in the composition of the exploited herring stock."

(ii) The objectives of the experiment are, according to the same Memorandum:

"(a) As in the 1957 /58 Bl0den tagging experiments, the main objective of the new experiment will be to obtain a minimum estimate of the proportion of the juvenile herring stock in the Bl¢den area taken by the fishery there. This estimate is required to assess the effect of the Bl!li'clen fishery on recruit­ment to the total adult herring· population in the North Sea. Further, provided adequate sampling for racial analysis is conducted, it is hoped also Lo provide estimates of its effec.:t on recruitment to each of the main spawning stocks separate!)'.

(b) In addition, it should provide valuable information on the distribution and migration pattern of the juvenile herring within and away from the Bl¢'clen area."

In view of the recent developments in the juvenile fisheries, the Working Group found it desirable to extend the area defined in the said Memorandum up to 58°N, and also into the Skag·erak, and has based its pla1ming upon this extension (see Figure l)*.

In order to cover the main period of the fisheries it is proposed to advance the time of the commencement of the experiment to 15 July 1969 ending on 1:"3 March 1970.

*Map, p. :n, Rapp. P. -v. Reun. Cons. int. Explor. Mer, 152, with sub­areas inserted.

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APPENDIX III Figure 1

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(iii) The experiment

(a) Ship The Working Group was informed by its Norwegian mem-ber that it was possible to hire a suitable Norwegian purse seiner with its gear and crew for a period of 8 months within the costs proposed in tht! budget. If a new vessel were to be hired the cost would most likely be of the order of D. Kr. 930 000, including all running costs (crew, suitablE> gear, insurance. fuel, food, etc.). The Working Group requested the Norwegian member, with the assistance of the General Secretary of ICES, to negotiate, if possible, the hire of a somewhat smalJer and older vessel welJ within the total cost of D. Kr. 900 000. The costs have to be made on the basis of a full 8 months charter. The period of hire should run from 15 July 1969 until 15 March 1970.

The operation of the vessel will be under the instructions of the supervisor, unless safety of ship or crew is involved . The supervisor will decide on the handling and disposal of all catches.

(b) P rsonne l At the request of the Working Group the Norwegian representative harl. investigated the possibility of hiring spedal person­nel for conducting the tagging. The Group considered it desirable that the "supervisor" and ''gunners'' should be Norwegians. The Institute of M<1rine Research in Bergen has kindly agreed to release a tagg·ing expert, Mr Sangolt, for 8 months to act as leader of the team ("super­visor") . The hi ring of the two "gunners'' for the duration of the exercise was not cons irlet'Ccl to offer much difficulty. If necessary, a third "gunner" might be ava ilahle from the Bergen Laboratory.

The contracts will be drawn up on the basis of a continuous sea­going availability.

The Group was informed that the supervisor's salary in the Norwegian service fo1· an equivalent tagg·ing <~Xl·n·iHe would h:ive Lwen approxi.matel,v D. Kr. 40 000, including sea-subsistence, health­insurance. soci:11 st.•curit_y payments, etc. In view of the high level of responsibilit~, for the sticcess of the operation and the condition of ser-­vice on a commercial vessel for 8 months, it was considered that an additional emolument of D. Kr. 10 000 should be marle, bringing the total sum to D. Kr. :)0 000.

The pruposed salary for the "gunners" is based on the payment of junior teehnicinns in the Norwegian service, which would :i rnount to approximately D. Kr . 80 000, including sca-subsit>tcnce, l1ealth-service. social security payments, etc.

Any approved travel expenses of the hired personnel would be according to ICES rates.

(e) .]).gging The type of tags to be used in the experiment will be the small "sprat ''--type tag. Although the ultimate aim is the release of 100 000 tagged fish, a preliminary order of SO 000 tags was considered adequate to start the experiment. The total cost of 100 000 tags would be D. Kr . 25 000. The necessity of purchasing three tagging guns, at the' cost of D K1·. 4 800 , will be left to the discretion of the supervisor, in consultation with the Chairman of the Working Group.

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The additional possibility of external tagging was considered, but the Group decided against it in view of the disappointing results with this type of tag from the 1957 /58 experiments.

Rewards The Group felt that the usual national reward for herring tag returns should be paid, which is of the order of D. Kr. 10 per return. The costs involved to pay the rewards were difficult to estimate, as they depend on the number of tags used and the fishing rate, the determination of which is the object of the experiment. The Group has therefore limited the sum available in the budget for rewards to D. Kr. 70 000, payable up to 1 January 1971. This would for example cover a 10% return of an effective release of 70 000 tags, compared with a 6% return in the previous experiment. Any rewards to be paid in excess of D. Kr. 70 000 or after 1 January 1971 will have to be paid by national governments of the country, where the tag is recovered, in accordance with established international practice.

(d) Boats and ancillary equipment During the tagging operation boats have to be used, and the Group recommends the use of two rubber boats, costing approximately D. Kr. 5 000 each. In addition it will be necessary to have keep nets and dip nets made at an approximate cost of D.Kr. 10 000.

(e) Tagging mortality In view of the deficiencies of the 1957 /58 taggings in respect of the determination of tagging mortality, the Group paid considerable attention to this subject. Apart from indirect esti­mates of tagging mortality, such as were made previously, some attempts to obtain direct estimates are desirable. The following methods were proposed:

1 The use of free-floating keep nets in the open sea with tagged and untagged herring, supplied by the purse seiner and attended by research vessels.

2 Holding live, tagged and untagged, herring, supplied by the purse seiner, in suitable containers on research vessels.

3 Experiments in keep nets in sheltered coastal waters and tanks in laboratories with locally-caught juvenile herring.

It is expected that attending research vessels will assist in carry­ing out Method 1. Dependent upon suitability of the research vessel and its facilities, it is hoped that some experiments by Method 2 would be made. Neither of the experiments mentioned under points 1 or 2 should be extended more than five days. Realizing the probably excellent facilities for executing Method 3 in several of the participating countries (Waddensea, Kieler Forde, Ringk!llbing, Limfjorden, Norwegian fjords, Swedish west coast and Scottish coastal areas), the Working Group strongly recommends that every effort should be made to obtain infor­mation especially on the influence of temperature and condition of the fish on tagging mortality.

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(f) Distribution of tags in time and space It is necessary that the tags should be distributed over a wide area throughout the course of the experiment in order to get tags into as many components as possible of the juvenile stocks of the North Sea herring.

It is realized that the tagging positions will be determined in the first place by the availability of suitable fish shoals. The distribution of fishing over recent years led the Group to establish four general tagging areas (see Figure 1). It is the intention that tags would be liberated within each of the areas within each month, depending upon the availability of fish as reported from the commercial fishery and research-vessel searching. In view of the location of some of the fish­ing grounds close to the Danish coast, permission has to be obtained for the vessel to fish within the Danish exclusive fishing limits.

It is estimated that an efficient tagging team can work at a rate of 200 tagged fish per hour. In order to minimize the effects of increased tagging mortality with time it was decided that tagging on a catch should be limited to about 5 hours from the start of the tagging. In this manner a batch liberation of 2 000 tagged fish would be the maximum, using two tagging teams as intended. At this rate 100 000 tags could be liberated in a minimum of 50 successful shots. In view of the dependence of tagging on suitable weather, wind-force 3 being most likely the limit, a number of 50 successful shots were considered to be a reasonable expec­tation of the experimental period, which includes the winter. An average of 9 to 12 working days per month could be expected according to meteorological observations.

(g) Research vessels It was considered necessary that during the whole experiment the purse seiner should be supported b:-,· at least one research vessel at the time. The work of the research vessel would be:

(i) to assist the purse seiner in locating suitable herring concentrations;

(ii) to carry out experiments to obtain estimates of tagging mortality (keep nets, tanks on board), and

(iii) to make hydrographic surveys to supplement observations made on the purse seiner.

The following time-table for research vessel assistance was pre­pared in October 1968, and the Working Group now expects that this plan can be carried out, perhaps with one reservation:

1969

August September October November December

Poland Denmark Poland Netherlands Norway

1970

January February

March

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Federal Republic of Germany International Young Herring Cruises, including ships of different countries France

Unfortunately it was reported that the Danish research vessel may have to be withdrawn from its commitment. The Working Group stresses the need for adequate research-vessel support during this month and has requested the Danish member to look into the possibilities of making alternative arrangements.

With the change in the proposed date of commencement, some adjustments would be necessary in the research vessel time-schedule. The French member will investigate the possibility of covering the month of July 1969 instead of March 1970.

While the research vessels are in attendance of the purse seiner the Group requests that the vessels take advice from the Supervisor on the purse seiner concerning the areas to be searched and the experi -ments on tagging mortality to be carried out.

(h) Purse-seiner reporting procedure It will be necessary for the Supervisor to report on his activfties at frequent intervals. These reports will be sent to ICES headquarters, which will be responsible for copying and distributing them immediately to members of this Group. Any communication arising from these reports should be sent to the Chairman of the Group and copied to ICES. The Chairman, or his delegate, will be the only member of the Group authorized to issue instructions to the Supervisor, such instructions normally being trans­mitted through ICES headquarters.

It is considered that a small group of three or four people, together with an ICES officer, should brief the tagging team on the commencement of the experiment, in Esbjerg. Additional meetings of members of the Group with the tagging unit or its Supervisor may be needed.

A letter of instructions for the Supervisor will be prepared, giving a more detailed description of the progTamme.

Arrangements will be made to keep the purse seiner informed of the positions of the Danish fleet.

(i) T a g r ecovery The success of the whole experiment is heavily dependent on a high efficiency of detection of the tags in all the major plants handling the herring catches from the North Sea and Skagerak. It is the considered opinion of the Group that it will not be worthwhile to carry out the experiment unless adequate facilities for tag recovery are available.

The countries which are expected to yield about 90% of the tag returns are Norway and Denmark. Some recoveries may be obtained in the Federal Republic of Germany and Sweden, and perhaps also Scotland.

It is understood that in Norway most of the plants are fitted with efficient magnets. Denmark reports efficient magnets in the major plant in Esbjerg, but other plants have either low efficiencies or were reported not to be equipped with mag11ets. Considering the predomi­nant position of the Danish fishery in the total catch of juvenile herring, for which a major part of the tag returns are to be expected, the Group strongly presses for adequate facilities for tag recovery in all the major plants in each port of that country.

The Memorandum of the experiment sent to the participating countri e s stated that tag recovery and magnet efficiency in a country's industry belonged to that country's responsibility. [n view of the urgency of arranging for adequate facilities for tag recovery, it is proposed that a recoverable sum of about D. Kr. 10 000 is reserved in the budget to meet any temporary financial difficulty on the immediate installation of suitable equipment.

Trig losses in the fish holds and in handling before reaching the magnets might be an important factor in recovery rates in some months and it was stressed that countries eoncerned should take measures to assess these losse!'-.

The advertisement of the tagging experiment is considered a

national responsibility and countries are urged to prepare posters for fish-meal plants. In addition, the Group will prepare a short account of the proposed experiment for publication in national fish-trade papers.

(iv) Statistics

The actual tagging is only a part of the experiment in question. No results can be obtained without detailed statistics on catch :rncl effort broken dovm b~· areas. which preferably should be ev811 smaller than the international statistical tTctangle.

At pi-esent (January l~JG9). the collection of detailed nationul statistics on juvenile fisheries in the North Sea and Skaii;erak is as shown below :

Denmark:

Sweden:

Norwav:

Federal Republic of Germany:

Salisfactory coverage of the Esbjerg l'ishery hroken down by lG x 15 nautical mile squares. The fishing from Thyboron being about 20% of the Rl0den fishing, is not sampled.

There is no information about the industrial fishing in Skagerak except for Danish and Swerli sh lanclings of adult herring in Hirtshals.

No information at all .

No information on effort available to the Group. Catch statistics are only broken down by fishing grounds.

No informntion.

It is evident that at the present level of statistical information no result C'an he obtain0.cl by the tagging experiment as envisaged. It is essential that at least !)0% of the Skagerak catches and 50% of the North Sea catches are

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covered in this respect, and it is the considered opinion of this Working Group that unless this demand for catch and effort data from landings is fulfilled the entire experiment will be a waste of money and manpower.

Concerning the adult fishery there is also need of statistical data. At the present time the following countries have given data as shown below:

Country Total landings Total landings Effort Gear in the North with reference data Sea, Skagerak to area and Kattegat

Denmark X X (partly) X (partly) X (partly) England X X X X France X X X X Germany (F. R. of) X X X X Netherlands X X X X Norway X X X Poland X X X X Scotland X X X X Sweden X USSR X ? ? ?

The following data are considered to be wanted for national correcting of statistical data, both for adult and juvenile fisheries:

(v)

1 Type of boat (gross tonnage, power)

2 Number of days at sea

3 Number of days fishing

4 Type of gear (seine, pelagic trawl, pair-trawl. bottom-trawl and drift net)

5 Quantity (of herring and eventually of by-catches) caught in each statistical area

13 Indication of fishing effort per statistical area ( e. g. seiners, number of shots; trawlers, number and duration of hauls).

Sampling

It will be necessary to sample the purse-seiner catches, the commercial landings and the research-vessel catches.

(a) Purse-seiner catches (i) Tagged fish The Group considered it important that the personnel of each team should, as far as possible, remain unchanged throughout the whole experiment. The teams will alternate in making length measurements of the fish, which they tag. During tagging records should be kept of the serial numbers of the tags used by each team in half-hourly periods.

(ii) Untagged fish A random sample of 100 fish will be taken from the remainder of the catch for length, age and weight determination.

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(b) Ccm,merci:.ll landings Random sarnµles of at least 100 fish should be taken daily in al1 major ports in which juvenile herring are landed (Denmark, Norway, Federal Republic of Germany) for length and weight measurements. Two samples per week should be treated for ag·e and other determinations. The position of the catching of these samples should be known.

(c) 11e ~ear ·h ves l'1 S In so far as research vessels during their scouting activities make trawl hauls. these should be snmplecl in ::i

similar manner to that used on the purse seiner.

(d) 8Hmplin g for stock anal y::;ii; In order to assess the effects of the juvenile fishery on the recruitment to the different components of the autumn-spawning North Sea herring (Downs. Bank and Buchan). special samples for separate analysis will be needed. As at p1·e sent it is uncertain whether adequate methods of stock analysis will be available for the young herring, it is proposed that aclditional samples should he deep-frozen, both on the purse seiner and in the ports. The samples should be replicates of those used for age analysis. Working up and analysing this material should be carried ou1. at national cost. The costs of deep-freezing these samples from the purse seiner have been estimated nt D. Kr. 2 000.

It cannot be expected that any results of this analysis will be available before 1975 a1. the earliest, to allow for the time to recruit­ment of the tagg·ed year-classes and the time-consuming anal_,·sis .

(e) Aduiliomtl observations At each tagging position surface and bottom temperature need to be recorded. Jt is proposed Lo use a bath_y­thermograph :-md it is hoped that this can be clone without cost to the

project.

(vi) The analysis and final re llll'l

An account or the cornlucl or the (!Xperin·,enl will lw made as so(Jn after the termination of tag·ging in March 1D70.

An analysis of the data. available up to January I 97 I. will lie made during spring l !171 At that time the necessar~ cornmen:ia l statistics of the 1970 fishery should be available. It is expected that a meeting of tht• full Group, necessary for nnalysin;.; tlw data and preparing a report, will at least require 10 days . Prnliminary data summarization will be carriL·d out b~· the Secretary of tlw Liaison Committee on :i continuous basis throughout the experiment LJnd up to January 1971, in preparation for the meeting. He will keep the members of the Working· Group informed about this preliminar.v ana­

lysis. Tt is hoped that this will provide a basis for informing the NEAFC at its meeting in May l971. The full report wil1 not be available heforc I D7~ .

Tags are expt'ded to be returned for some time after ,January 1U71. An eventual analysis ol these data, coming from the adult fish, will have to be con1,;iclered at a later date.

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(vii) M:rnagerncnt of the experiment

The Group felt that the preparation of the experiment and the day-to­day management should be executed from the ICES headquarters. It is understood that the individual members of the Group will assist ICES officers in these tasks. ICES will be responsible for contracting ship and µersonnel, purchasing the necessary equipment, maintaining the reporting system of the operation and assisting in the statistical analysis of the data.

(viii) Costs

ICES Item D.Kr . Account No.

B. 2 ShiQ hire 930 000 ( 900 000)

B. 3 P ersonnel: Supervisor, basic salary 40 000 Supervisor, increment 10 000 2 "gunners" @ 30 000 60 000 110 000 ( 126 000)

B.4 Miscellaneous: 100 000 tags 25 000 3 guns for tagging 5 000 Rewards 70 000 Keep nets, dip nets, etc. 10 000 2 rubber boats 10 000 Deep-freezer 2 500 Renting of deep-freezing

comp. (Esbjerg) 2 500 Telegrams, echo-sounder

paper, pilot charges, etc. 10 000 Meetings 40 000 Inspection and travel 10 000 Suspense accounts (magnets) 10 000 19;':i 000 140 000)

B. 5 Contingencies (unforeseen) l;) 000 84 OQ_Q}

250 000 (1 250 000)

Figures in parentheses are from the preliminary cost estimate.

Charlottenlund, 20-22 January I !169

J. J. Zijlstra (Chairman) H. Ackefors A. C. Burd S. Haraldsvik* Cl. Nedelec

J. A. Pope K. Popp Madsen G. Wagner The General Secretary

*took part in the meeting on the 20th only.

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APPENDIX IV Instructions for the Supervisor of the Bliden Tagging Experiment

l During the Experiment a log-book (Norwegian type) will be kept, report-ing on the day-to-day activities of the purse seiner, giving information on positions, weather, state of the sea, etc. The daily report should include brief information on hydrographical data collected, tags liberated (series) and samples collected.

2 Tag·ging should be aimed at an equal distribution of tagged fish over the areas I -IV, indicated in Figure 1. In principle and depending on the situation, at least one liberation should be made per month in each of the four areas.

3 To locate herring concentrations use can be made of assistin_.!, research vessels. The supervisor will be informed about the cruise schedules of the different research vessels. The supervisor should keep regular radio contact with the assisting vessels, using the 2056 K. C. wave-length, if possible, and calling as often as necessary, but at least once a day at 9 pm GMT. The supervisor should indicate the area to be searched for herring shoals to the research vessel and include bottom and surface temperatures, recorded by the research vessel, in his log-book.

4 The supervisor will take note of the catch positions of the Danish pair-trawl fleet, fishing for immature herring, of which he will be regularly informed.

5 At each tagging location the supervisor should keep note of all relevant information, as position, date, weather, catch, etc., on a special tagging­sampling form, issued to him (Appendix 2). All information requested on these forms should be recorded.

6 Tagging teams should be kept unchanged during the whole eight-month period. During each liberation the series of tags, liberated by each team, should be recorded. Tagging on a single catch should be restricted to about five hours after the start of the tagging operation. Series liberated in the first, second, third, fourth and fifth hour after the start of the experiment should be recorded. In addition, records should be kept about the condition of the fish liberated, as A = undamaged, B slightly damaged. Fish which are more than slightly damaged should not be used. Information on condition should be recorded for a group of fish liberated by a single team in a given hour, noting percentages condition A and B, rather than the condition of indi -vidual fish. The information concerning series of tags by teams per hour and about the condition of the fish should be recorded in the special tagging­sampling form.

7 From each catch two random samples of 50 fish should be taken. The sampling procedure should be carried out according to instructions (see Appendix 1) . One of these samples will be deep-frozen for a special analysis ashore, noting position and data of catch. The total weight and the length­composition of this sample should, however, be recorded (1/2 cm below). Of the second sample the total weight will be recorded and from each individual fish the length (to the 1/2 cm below) and age will be determined. The age will be obtained from otoliths. Length and age, together with the length of the special sample, will be entered in the tagging-sampling form.

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8 At 8uitable times experiments will be carried out to obtain estimates of tagging mortality. In principle and depending on circumstance two expcl'iments are thought advisable per month. Two types of experiment are needed:

1 Keep nets A hundred tagged and a hundred untagged herring are kept for about five days in two separate keep nets. drifting in the sea. A research vessel is watching these keep nets during this period and determines after five days the number of live herring in both nets. In case of deteriorating weather an experiment has to be finished before the end of the five-day period. The herring has to be tagged by the tagging teams of the purse seiner, the herring has to be measured and the condition at the start of the experiment recorded.

2 Tanks In the tanks on board the purse seiner 100 tagged and 100 untagged herring are stored for about five days. After that period the number of live herring in each batch is determined. In case of troubles with the tanks on board the purse seiner the same experiment can be carried out on board a research vessel, the herring being tagged by the purse seiner's tagging teams. Condition and length of the herring in these experiments have to be recorded.

The results of all experiments should be recorded on a special tagging­mortality form, designed for this purpose (Appendix :3).

9 The supervisor should report regularly, at least by half -month periods, about the progress of the experiment. Reporting should be done either by letter or by radio to ICES headquarters. The report should contain informa -tion about tagging positions, numbers tagged per position. and serial numbers liberated at each position. Additional information on difficulties encountered, contact with research vessels, progress made in tagging-mortality experi -ments should be added. In the case of reporting by letter duplicates of log-book sheets. tagging-sampling and tagging-mortality forms should be included.

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APPENDIX V The Scientific Working Groups and the Management Committee

An ad hoc group met during the ICES Statutory Meeting in 1967 to draw up a design and to cost an experiment intended to provide answers to the questions posed by the Liaison Committee. The ad hoc Group was:

Prof Dr G. Hempel Mr A. C. Burd Dr 0. Dragesund Mr S. Haraldsvik Mr B. B. Parrish Mr K. Popp Madsen Dr A. Schumacher Dr J. J. Zijlstra

Federal Republic of Germany, Chairman UK Norway Norway UK Denmark Federal Republic of Germany Netherlands

Following further discussions between interested countries on the share of the costs of such an experiment, the ICES Pelagic Fish (Northern) Commit­tee set up a Working Group to design an experiment in detail within the available financial resources. The Working Group was:

Dr J. J. Zijlstra Dr H. Ackefors Mr A. C. Burd Mr S. Haraldsvik Mr C. Nedelec Mr J. A. Pope Prof Dr J. Popiel Mr K. Popp Madsen Dr A. Schumacher Mr J. Miller Christensen Mr H. Tambs Lyche

Netherlands, Chairman Sweden UK Norway France UK Poland Denmark Federal Republic of Germany ICES Statistician ICES Secretary General

In addition the ICES Consultative Committee set up a Management Committee. The Members of this Group were:

Mr K. Ldkkegard Mr R. Letaconnoux Dr K. Schubert Mr Th. J. Tienstra Dr O. Dragesund Dr J. Hult Dr H. A. Cole Mr H. Tambs Lyche

Denmark France Federal Republic of Germany Netherlands, Chairman Norway Sweden UK ICES Secretary General

Five meetings of the Working Group have been held. There have been changes in national participation dependent on the changing subject matter as the experiment has progressed from planning, to execution, and the final statistical analysis. The attendance at the various meetings is summarized below:

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Participants 1969 1971 1973 1974

20-22 Jan 29 Mar- 6-10 Sept 27 Jun- 20-25 May 2 Apr 3 Jul

Dr H. Ackefors Sweden j j j Dr E . Bakken Norway j Mr H. Becker Netherlands j j Mr A. C. Burd UK j j j Chairman Chairman Dr H. Dornheim Federal Republic j

of Germany Mr S. Haraldsvik Norway j Mr H. Lassen Denmark j j Mr A. Maucorps France j j I Mr C. Nedelec France j Mr M, D. Nicholson UK J J Mr J. A. Pope UK j J j J J Mr K. Popp Madsen Denmark J j J J J Mr G. Sangolt Norway J j Mr(/). Ulltang Norway j Mr G. Wagner Federal Republic j j J

of Germany Dr J. J. Zijlstra Netherlands Chairman Chairman Chairman Mr 0. J . (/)stvedt Norway J J ICES General Secretary J J J J J ICES Statisticians

Mr J. M~ller Christensen J J J J Mr D. Griffiths J

In addition to these official meetings, a number of informal meetings were held outside the budget of the experiment in conjunction with other meetings. These were:

Dublin London

Charlottenlund

30 September 1969 6 May 1970

24 September 1970

ICES Statutory Meeting Northeast Atlantic Fisheries Commission ICES Statutory Meeting

- 91 -

APPENDIX VI "Gerda Marie": tagging and sampling log

I ci,;;; hi l 'Di-: N ~'AGGINC EXPERIMENT - TAGGING AND SAMPLING

Ct-:Nl•:Ri\l . INFORMA1'ION TAGGING

Tagging Team 1

Experiment No. : 1 Serial No.

Day-Month-Year: 25. 7. 69 Condition of fish

Start 1 A B

Position: 57o 52 1 North latitude 1st hour 1- 200 10° 30 1 East longitude

Statistical rectangle: 1439 bUl- ovv

2nd hour 701- 800 an1-1nnn

Surface temperature: 15. 7 1101-1200 3rd hour 1301-1400

Bottom temperature: 9. 5 (50 M)

4th hour 1501-1700

Wind force : 16 1801-1900

Wind direction: 01 5th hour

Sea state: 3

Current: Var. easterly 6th hour

Start of tagging: 0130 Total tagged 996

End of tagging: 0530 Tagging Team 2

Serial No, Condition of fish

Notes: 30 tons caught. Condition of tn gged fish not determined. Start 201 A B

1st hour 201- 500

2nd hour 601- 700 801- 900

3rd hour 1001-1100 1201-1300

1401-1500 4th hour 1701-1800

101)1 _onrn

5th hour

6th hour

Total tagged 1000

No. of B-condition fish in experiment, per mille I SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12 . 5 13 13 . 5 14 14 , 5 15 15 . 5 16 16 . 5 17 17 . 5 16 HJ , 5 19 19 . 'i 20 1 20 . 5 -21 7 5 21.5 6 7 22 11 9 22 . 5 11 7 23 5 9 23 . 5 2 2 24 3 5 24 .5 1 -25 2 ~

25.5 1 -26 - 2 26 . 5 - 1 27 1 27 , 5 28 28 . ~

Total 50 50 42 8

Weight 5750 5855

APPENDIX VI (Continued) - 92 -

rc,:s !lL0DEN TAGGING EXPERIM!lNT - TAGGING AND SAMPLING

GENERAL INFORMATION TAGGING

~'agging Terun 1

E:xperirnent No.: 2 Serial No .

Day-Month-Year: 31. 7. 69 Condition of fish

Start 2101 A B

Position: 550 02 I North latitude 1st hour 2101-2400 15 05° 36 I East longitude

Statistical rectangle: 0934 2nd hour 2701-3000 10

Surface temperature: 17.6 17. 8 ord hour 3601-3900 7 Bottom temperature: 7.1 7.1

4th hour ·wind force: 05

Wind direction: 36 5th hour

Sea state: 3

Current: 0 6th hour

Start of tagging: 1305 Total tagged 900 32

End of tagging: 1605 Tagging Team 2

Serial No. Condition of fish

Notes : 30 tons caught. Start 2401 A B

1st hour 2401-2700 10

2nd hour 3001-3300 15

3rd hour 3301-3600 13

4th hour

5th hour

6th hour

Total tagged 900 38

No , of B-condition fish in ~xpe riment, ner mille I 39

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm. below Sample 1 - deep frozen Sample 2 0 I II+

11. 5 12 12. 5 13 13.5 14 14, 'i 15 15.5 16 16.5 17 17 . ', 18 1 Hl,5 -19 2 19.'i -20 2 2 20.5 4 3 21 4 6 21.5 7 8 22 9 11 22.5 6 3 23 7 2 23.5 5 5 24 2 4 24. 5 - 4 25 1 l 25.5 1 26 26.5 27 2'/. ~ 28 28,', .. - ·--•·-Total 50 50 41 9

Wei.ghl 4700 5000

- 93 -APPENDIX VI ( Cont i nued )

1c1,: :; li l,0DEN 1'AGGINC EXPERIM!lNT - TAGGING AND SAMPLING

C1,: t11•:llJ\I, IN!'0RJ,!J\1'ION TAGGING

Tagging Team 1

l•:x p12rim1..~nt No . : 3 Ser i al No,

D~.:i ;r-T'-lonth-YeaI" : 1. 8. 69 Condition of fish

Start 4001 A Il

Posit ion : 55 ° 04 1 Nor th l a t i tude 1st hour 4001-4300 16

05° 56 1 Ea~t l ongitude 5301-5400

Statistical rectangl e : 0934 2nd hour 5401-5800 13

Surface tempe r a ture: 18.2 18.4 3rd hour 5801-6000 6

Bot tom temper a ture : 7.4 7 . 9

4th hour Wind force: 05

Wind di rection : 12 5th hour

Sea state : 3

Current : 05 0.5 6th hour

Start of tagging: 1415 Total tagged 1000 35

End of t agging : 1730 Tagging Team 2

Serial No . Condition of fish

Note s: 10 tons caught Start 4301 A B

1st hour 4301-4700 19

2nd hour 4701-5100 17

3rd hour 5101-5300 14

4th hour

5th hour

6th hour

Total tagged 1000 50

No , of B- condi tion fish i n experiment , per mille I 38

SAMPLING

Length to Length c omposit ion Age composition of sample 2 ½ cm, be l ow Sampl e 1 - deep f r ozen Sample 2 .Q I II+

11. 5 12 12. 5 13 13 . 5 14 14 , 5 15 15 . 5 16 16 , 5 17 17, 5 18 Hl , 5 1 2 2 19 2 -19 ,5 5 3 3 20 •I 3 3 20 , 5 3 5 5 21 8 11 11 21. 5 9 5 5 22 8 7 7 22 . 5 3 4 4 23 2 5 2 3 23 . 5 2 1 1 24 1 - -24 , 5 - 2 2 25 - l l 25 . 5 1 1 1 26 -26 . 5 -27 -27 , 5 1 28 28 , 5

Total 50 50 42 8

ileight 4500 4500

- 94 -APPENDIX VI (Continued)

~ING EXPERIMENT - TAGGING AND SAMPLING

Gd.: r ,~ '. .. TAGGING

Tagging Team 1

Experiment No . : 4 Serial No,

Day-Month-Year: 4/5 ;8 .69 Condition of fi8h

Start 6001 A B

Position: 540 41 1 North latitude 1st hour 6001- 6450 13 05° 30 1 East longitude

Statistical rectangle: 0834 2nd hour 7101- 7400 10

Surface temperature: 18.9 5/8 0845 3rd hour 7401- 7800 12

Bottom temperature: 8.5

4th hour 7801- 8100 10 Wind force: 03

Wind direction: 111 5th hour

8101- 8200 13 Sea state : 2 9501- 9800

Currenti 0 6th hour 9801-10000 7

Start of tagging: 4/8 2115 Total tagged 2050 65

End of tagging: 5/8 1215 Tagging Team 2

Serial No , Condition of fish

Notes: 5 tons caught. Start 6451 A B

1st hour 6451-6750 15

2nd hour 6751-7100 11

5/8 0845 3rd hour 8201 -8600 18

4th hour 8601-8900 21

5th hour 8901-9200 13

6th hour 9201-9500 11

Total tagged 1950 SD

No , of B-c ondjtion fish in experiment, per mille I 39

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm.below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12,5 13 13, 5 14 14,5 15 15.5 16 16.5 17 17 ,5 1 1 18 2 1 1 10.5 1 - -19 4 7 7 19,5 4 5 4 1 20 8 5 5 -20,5 9 9 9 -21 4 6 5 1 21.5 5 5 5 -22 3 3 2 1 22.5 3 3 2 1 23 2 - - -23 , 5 1 2 1 1 24 3 2 1 1 24 , '> - - -25 - - -25.5 1 1 1 26 26.5 27 27 . 5 28 28 , 5 .

Total 50 50 43 7 Weight 4000 3850

- 95 -APPENDIX VI (Continued)

ICJ-:S lll,ODEN 1'AGGINC EXPERIMENT - TAGGING AND SAMPLING

GlilffiRAL INFORNA1'ION 1'AGGING . .,. __ Tagging 1'cam )

Experiment No. : 5 Ser ial No,

Day-Month-Year: 7.8.69 ;:0wJ.ition · ,1 J"iGh

Start 10001 I, ll

Position: 54° 57 I North latitude 1st hour 10001-10450 16 05° 20 1 EaAt longitude

Statistical rectangle: 0834 2nd hour 11301-11700 16

Surface t emperature: 19.3 3rd hour ll 701-11900 10 Bottom temperature: 7. 7

4th hour Wind force: 04

Wind direction: 31 5th hour Sea state: 2

Current: 0 6th hour

Start of tagging: 1110 Total tagged 1050 42

End of tagging: 1445 Tagging Team 2

Serial No, Condition of fish

Notes: Start 10451 A B

1st hour 10451-107 50 10

1300 2nd hour 10751-11200 14

3rd hour 11201-11300 11901-12000

12

4th hour

5th hour

6th hour

Total tagged 950 36

No. of B-condition fish in experiment, per mille I 39

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12,5 13 13.5 14 1'1. ~ 15 15 . 5 16 16 . 5 17 17 . 5 18 I 1 1 10 . 5 - 1 I 19 4 - -19 , 'i 4 4 4 20 3 3 3 20, 5 3 7 7 21 4 7 7

21.5 11 6 6 22 5 4 4 22.5 8 4 4 23 2 6 3 :1 23.5 1 3 I 2 24 - 4 4 24 , 5 2 25 1 25. 5 1 26 26.5 27 27. 5 28 28, 5

·- --Total 50 50 41 !l

Weight 4450 4500

- 96 -APPENDIX VI (Continued)

ICES BL<JJJ~ll' TAGGING EXPERIMENT - TAGGING AND SAMPLING

GlcNllRAL INF0RMA~'ION TAGGING

Tagging Te8lll 1

xreri.ment No.: 6 Serial No .

J\ay-Month-Year: 20.8.69 COll<i.i 1 l•) • I r__1f fish

Start 12001 H

Position: 560 25 1 North latitude 1st hour 12001-12200 13 Off' 331 East longitude

Gtatistical rectangle: 1135 2nd hour 12201-12400 14

Su.rface temperature: 19. 0 18.9 3rd hour 12401-12600 14 Bottom temperature: 7. 0

4th hour 12601-12800 14 Wind force: 08

Wind direction: 25 5th hour 12801-13000 15 Sea state: 3

Current: 0 6th hour

Start of tagging: 0800 Total tagged 1000 70

End of tagging: 1300 Tagging Team 2

Serial No . Condition of fish

Notes: O. 5 ton caught. 12 hours from catch to tagging. Start 13001 A B

1st hour 13001-13200 9

2nd hour 13201-13400 12

3rd hour 13401-13600 12

4th hour 13601-13800 13

5th hour 13801-14000 17

6th hour

Total tagged 1000 63

no. of ]-condition fish in experiment, per mille I 67

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11.5 1 1 12 2 7 7 12 . 5 11 8 8 13 9 8 8 13.5 7 3 3 14 3 6 6 111 . 5 2 2 2 15 - -15 . 5 - -16 - -16 , 5 - -17 - -17 . 5 1 2 2 18 1 :\ 3 HJ . 5 4 ~ 3 19 1 3 3 19 , ', - J 1 20 3 1 I 20.5 2 1 I 21 - - -21.5 1 1 1 22 1 22.5 -23 1 23.5 1 24 24.'i 25 25.5 26 26 . , 27 27. ~ 2L' 2&. 5

·- - -Total 50 50 35 };)

'Nt:·:L~tllt 1750 1400

- 97 -APPENDIX VI (Continued)

lCi•::; Hl,l'Dr-;N 'l'ACGING EXPERIMENT - TAGGING AND SAMPLING

Gi•:NJ.:RAL INL'0RNA1'ION 'l'AGGlHG

Tagging 'J\ a1:1 J

i:.:xp0ri111C nt 1:0.: 7 Serial Ho.

Day-Nonth- ':car: 28.8.69 ;:oncli tion rJJ' fi~h

Start 14001 f, B

Position : 570 34' North latitude 1st hour 14001-14400 32 110 381 East longitude

Statistical rectangle: 2nd hour 14401-14700 34

Surface temperature: 17.9 17.8 3rd hour 147nJ -1 :;oou 18

Bottom temperature: 10.9

4th hour Wind force: 11

Wind direction: 27 5th hour Sea state: 3

Current: s ½ knot 6th hour

Start of tagging: 1500 Total tagged 1000 84

End of tagging: 1745 Tagging Team 2

Serial tlo , Condition of fish

Notes : 2 . 5 tons caught . Start 15001 A B

1st hour 15001-15400 34

2nd hour 15401-1 5700 32

3rd hour 15701-16000 18

4th hour

5th hour

6th hour

Total tagged 1000 84

No, of D-condition fiDh in exp0riment, per mille I 84

SAMPLING

Length to Length composition Age colllposition of Gample 2

½ cm. below Sample 1 - deep frozen Sample 2 0 I II+

11. 5 12 12. 5 13 13 , 5 14 14,5 15 15 , 5 16 16.5 17 1 l I 17 . 5 - 1 l 18 1 2 2 HJ,5 2 1 1 19 3 5 3 19 . 5 2 5 1 ,j

20 -1 3 ! ,j -20. 5 4 4 4 21 ,i 2 2 21.5 4 3 2 1 22 G 4 4 -22. 5 3 6 G -23 9 8 7 1 23.5 2 3 1 2 24 3 1 1 24.5 2 1 1 25 ·--- . 25- '.i 26 26 , 5 27 27 . ·, i/B 28 , ' - ----· . - - -To:..c,~ 50 50 46 4 •-· - - ----

',;e~1j,1 4450 4100

- 98 -APPENDIX VI (Continue~)

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GJ-:NERAL INFORMATION TAGGING

Tagging Team 1

Experim1·nt No.: 8 Serial No.

Day-Month-Year: 5.9.69 Corn.liUon of fish

Start 16001 I, B

Position: 56° 28 1 North latitude 1830 1st hour 16001-16400 30

06 o 451 Eaat longitude

Statistical rectangle: 1135 2030 2nd hour 16401-16700 39

Surface temperature: 15. 4 2130 3rd hour 16701-17000 18

Bottom temperature: 7.5

4th hour Wind force: 11

Wind direction: 29 5th hour

Sea state: 3

Current: 0 6th hour

Start of tagging: 1830 Total tagged 1000 87

End of tagging: 2230 Tagging Team 2

Serial No. Condition of fish

Notes: 1. 5 tons caught. Start 17001 A B

1st hour l 7001-17400 32

2nd hour 17401-17700 44

3rd hour 17701-18000 30

4th hour

5th hour

6th hour

Total tagged 1000 106

No. of B-condition fish in experiment, _rer mille I 97

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12 . 5 1 3 3 13 3 7 7 13 . 5 16 15 15 14 13 14 14 14 . 5 6 5 5 15 5 2 2 15.5 2 1 1 16 1 -

16.5 - -17 - -17.5 1 -18 - 1 1 Hl.5 - - -19 - - -19 , 'i - 1 1 20 1 - -20.5 - - -21 1 - -21.5 - -22 1 1 22.5 23 23.5 24 24.'i 25 25.5 26 26.5 27 27.5 20 28,5

-Total 50 50 47 3

Weight 1200 1150

- 99 -APPENDIX VI (Continued)

ICES llL0DEN 'PAGGINC EXPERIMENT - TAGGING AND SAMPLING

G~NERAL INFORNATION TAGGI NG

Tagging '11eam I

Experiment No . : 9 Serial No,

Day- Month- Year : 8 . 9. 69 Corn.Ji tion uf fish

Start 18001 f, B

Pos ition : 56 ° 24 • North latitude 1030-1130 1st hour 18001-18400 39

06 o 48 1 East longi tude

Statistical rectangle: 1135 1230-1330 2nd hour 18401 -18800 38

Sur£ace temperature: 14.7 1330-1400 3rd hour 18801-19000 15

Bottom tempe rature : 7.6

4th hour Wind force: 04

Wind direction: 21 5th hour Sea state: 2

Current: 0 6th hon:r

Start of tagging: 1030 Total tagged 1000 92

End of tagging: 1400 Tagging Team 2

Seri al No. Condition of fish

Notes: 10 tons caught . St art 19001 A B

1st hour 19001-19400 45

2nd hour 19401 -19800 32

3rd hour 19801- 20000 13

4th hour

5th hour

6th hour

Total tagged 1000 90

No, of B- condition fi8h in experiment, per mille I 91

SAMPLING

Length to Length composition Age composit i on of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12.5 1 13 2 2 2 13.5 9 6 6 14 7 10 10 111 . ~ 11 12 12 15 8 7 7 15 . 5 7 9 9 16 4 1 1 16 . 5 - 1 1 17 · - -17 . 5 - -18 - 1 1 HJ , 5 - - -19 1 - -19 . 5 - -20 1 1 20.5 21 21.5 22 22.5 23 23.5 24 24 .5 25 25.5 26 26.5 27 27. 5 28 28, 5

- - -Total 50 50 48 2 We.ight 1300 1350

- 100 -APPENDIX VI (Continued)

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GBIIBRAL INFORMATION TAGGING

Tagging Team 1

Experiment No , : 10 Serial No ,

Day-Month-Year: 9.9.69 Condition of fish

Start 20001 A B

Position; 55° 59' North latitude 1st hour 20001-20500 32 07° 17 1 East longitude

Statis tical r ec tangle : 1036 2nd hour 20501-21000 34

Surface temperature : 16 . 45 3rd hour Bottom temperature: 12.0

4th hour Wind force: 04

Wind direct ion: 11 5th hour Sea state: 2

Current : 0 6th hour

Start of t agging: 1800 Total tagged 1000 66

End of tagging: 2000 Tagging Team 2

Serial No . Condition of fish

Notes : 1. 5 tons caught. St art 21001 A B

1st hour 21001-21500 37

2nd hour 21501-22000 40

3rd hour

4th hour

5th hour

6th hour

Total tagged 1000 77

No, of B-condition fish in experiment, per mille I 72

SAMPLING

Length to Length composition Age composition of sample 2 1 cm, below "2" Sample 1 - deep frozen Sample 2 .o I II+

11. 5 12 12 , 5 13 1 13. 5 2 2 2 14 6 5 5 1.1. o 6 8 8 15 8 14 14 15. 5 11 9 9 16 6 6 6 16 . 5 3 l 1 17 1 -17. 5 - -18 l 3 3 10 . 5 3 l l 19 1 - -1g,o 1 l 1 20 20. 5 21 21. 5 22 22. 5 23 23. 5 24 24. 5 25 25. 5 26 26. 5 27 27 , 5 28 28 , 5

Total 50 50 45 5

Weight 1600 1600

- 101 -APPENDIX VI (Continued)

rci;s llLODf::N TAGGING EXPERIMENT - TAGGING AND SAMPLING

m:Ifr:lu\ I INFORMATION TAGGING

Tagging Team 1

txperirnent No.: 11 Serial No.

Day-Month-Year: 15 .9.69 Condition oJ' fish

Start 22001 A B

Pos i tion: 55° 01 1 North latitude 1st hour 22001-22200

30 07° 03 1 ~ast longitude 22501-22600

Statistical rectangl e : 0936 2nd hour 22601-22800

34 22201-22300

Surface temperature : 17.4 3rd hour

Bottom temperature: 14.0

4th hour Wind force: 05

Wind direction: 04 5th hour Sea state: 3

Current : NNE 1 knot 6th hour

Start of tagging: 1630 Total tagged 600 64

End of tagging: 1815 Tagging Team 2

Serial No . Condition of fish

Notes: 0. 1 ton caught. Start 22301 A B

1st hour 22301-22600

36 23101-23200

2nd hour 22801-23000 24

3rd hour

4th hour

5th hour

6th hour

Total tagged 500 60

Eo. of D-e:ondition fish in experiment, r,er mille I 113

SAMPLING

Length to Length composition Age composition of sample 2 ¼cm.below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12 . 5 13 13 . 5 3 1 1 14 4 7 7 14 . 'j 10 10 10 15 13 15 15 15 . 5 11 9 9 16 5 2 2 16 .5 2 1 1 17 - 1 1 17 . 5 - 1 1 18 1 2 2 10 . 5 1 1 1 19 .19 . 5 20 20.5 21 21. 5 22 22. 5 23 23. 5 24 24. 5 25 25.5 26 26.5 27 27. 5 28 28 . 5

-- -1'otal GO 50 46 " Weight 1500 1550

- 102 -APPENDIX VI (Continued)

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

Glc:NERAL INFORMATION TAGGING

Tagging Te8Jll 1

Experime nt No.: 12 Serial No,

Day-Month-Year: 19.9.69 Condition of fish

Start 24001 A B

Position: 540 13 1 North latitude 1st hour 24001-24300 34

03° 40 1 East longitude

Statistical rectangle: 0732 2nd hour 24301-24600 33

Surface temperature: 16.1 1600-1700 3rd hour 24601-24800 22

Bottom temperature: 11. 8

4th hour Wind force: 05

Wind direction: 10 5th hour Sea state: 3

Current: Southerly 1 knot 6th hour

Start of tagging: 1330 Total tagged 800 89

End of tagging: 1700 Tagging Team 2

Serial No , Condition of fish

Notes: 0. 2 ton caught. Start A B 23001

1st hour 23001-23100 23201-23400

42

2nd hour 23401-23700 39

1600-1700 3rd hour 23701-23900 22

4th hour

5th hour

6th hour

Total tagged 800 103

No, of ]-condition fish in experiment, per mille I 120

SAMPLING

Length to Length composition Age composition of sample 2 ½cm.below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12 , 5 13 13 , 5 2 1 1 14 7 3 3 14 , 5 22 9 9 15 18 10 10 15.5 7 7 7 16 5 1 1 16,5 2 -17 1 -17 .5 1 1 1 18 2 1 1 10.5 3 3 3 19 5 4 4 19,5 5 1 1 20 9 4 4 20,5 7 - -21 2 1 1 21.5 2 3 3 22 3 1 1 22.5 2 23 1 23,:i 3 24 1 24,5 ' 25 25,5 26 26.5 27 27,5 28 28,5

Total 110 50 31 19 Weight 5000 2000

- 103 -APPENDIX VI (Continued)

1cI•::; hi,~'lJdl r.rAGGING EXPERIMENT - TAGGING AND SAMPLING

GJ<I·fi•:H.i1 I, 1rworu,:1\'l'h1I-J TAGGillG

Tagging T,•am 1

i'.:xpe1·imc-nl ::J.: 13 Serial No,

Day-Month-Year: 10.10.69 Condition of fish

Start 25001 f, ll

Position: 59° 35 1 North latitude 1s t hour 25001-25300 31 10° 391 Ea8t longitude

Statistical rectangl e : 17 39 2nd hour 25301 -25500 18

Surface temperature : 12.6 3rd hour Bottom temperature:

4th hour Wind force: 0

Wi nd direction: 0 5th hour Sea state: 0

Current: 0 6th hour

Start of tagging: 0900 Total tagged 500 49

End of tagging: 1100 ~•agging Team 2

Serial No. Condition 01' fish

Notes: 15 tons caught. Herring kept in keepnet fo r 5 days before Start 25501 A B tagging but seemed to be of normal condition on release .

1st hour 25501-25800 31

2nd hour 25801-26000 21

3rd hour

4th hour

5th hour

6th hour

Total tagged 500 52

No . of B-condition fi~h in experiment, per mille I 101

SAMPLING

Length to Length composition Age composition of sample 2

½ cm . below Sample 1 - deep frozen Sample 2 0 I II+

11. 5 12 12 .5 13 13. 5 14 1 14- 5 -15 -15. 5 -16 1 1 1 16.5 2 2 2 17 3 5 ~

17 . 5 4 6 6 18 8 11 11 Hl . 5 6 7 7 19 12 9 9 19 , ', 6 5 5 20 2 3 ~

20.5 1 1 1 21 2 21.5 1 22 1 22 . 5 23 23 . 5 24 24, 5 25 25.5 26 26 . 5 27 27. 5 28 20. ~ - ·-----· . -Totol 50 50 50

---Weif).t 2600 2450

-104 -APPENDIX VI (Continued)

JCI•::: HLODJ<:N ~•AGGING EXPERIMBNT - TAGGING AND SAMPLING

l~I l\•<hi\ I, INH)H.~1N11ION TAGGING

Tagging Team 1

i•: x l'l"l'intL'll l Nl' .: 14 Serial No .

Da_y-rlnntl,-\ e:1 r : 15. Jll. liD Condition of fich

Start 26501 A B

rosjtion: 58° 05 1 Nortli latitude 1st hour 26501-26800 34 06° 31 1 Rast longitude

Statistical rectangle: 1535 2nd hour 26801-27000 25

Surface temperature : 12.0 3rd hour Bottom temperature:

4th hour Wind force: 03

Wind direction: 20 5th hour Sea state : 2

Current: 6th hour

Start of tagging: 0800 Total tagged 500 59

End of tagging: 0930 Tagging Team 2

Serial No. Condition of fish

Notes: 15 tons caught . The same catch in the Oslofiord from which the mortality experiment was carried out.

Start 26001 A B

1st hour 26001-26300 30

2nd hour 26301-26500 20

3rd hour

4th hour

5th hour

6th hour

Total tagged 500 50

No. of ] - condition fish in experiment, per mille I 109

SAMPLING

Length to l,ength composition Age composition of sample 2 1 cm. below 2 Sample 1 - deep frozen Sample 2 0 I II+

11. 5 12 12. 5 13 13. 5 14 u .. 5 15 15. 5 16 1 16.5 1 1 1 17 - 2 2 17.5 1 3 3 18 8 7 7 10 .5 11 8 8 19 10 13 13 19, 5 6 G 6 20 7 6 6 20,5 3 - -21 - 3 3 21.5 1 - -22 - 1 1 22.5 -23 1 23.5 24 24 , 'l 25 25.5 26 26 .5 27 27.5 28 28, 5

Total 50 50 50

Weight 2700 2650

- 105 -APPENDIX VI (Continued)

1 Ci•:~~ til.l'Di-:tl '1'1\GGING BXPERlMI,:NT - TAGGING AND SAMPLING

Ci<lii-:!lJ\I. l!WORfiA'l'ION 1'AGGING

Tagging T<·am 1

ExpL.,,rimen L ML).: 15 Serial No ,

]lay-Month-Year: 23.10. 69 Conclition ol' fish

Start 27001 A IJ

Position: 56° 30 1 North latitude 1st hour 27001-27300 21 07° 02 1 EaRt longitude

Statistical rectangle: 1236 2nd hour 27 301-27700 26

Surface temperature: 11.7-11.6 3rd hour 27701-28000 19 Bottom temperature: 11. 7-11. 8

4th hour Wind force : 19

Wind direction: 18 5th hour Sea state: 3

Current: N ½ knot 6th hour

Start of tagging: 0800 Total tagged 1000 66

End of tagging: 1100 Tagging Team 2

Serial No. Condition of fish

Notes: 5 tons caught. 14 hours from catch to tagging. Start 28001 A B

1st hour 28001-28300 29

2nd hour 28301-28700 38

3rd hour 28701-29000 17

4th hour

5th hour

6th hour

Total tagged 1000 84

No. of B-condition fish in experiment, per mille I 75

SAMPLING

Length to Length composition Age composition of nample ., L

½ cm. below -Sample l - deep frozen Sample 2 0 I II+

11.5 12 12 . 5 13 13 . 5 14 14 . 5 4 15 9 3 3 15.5 15 11 11 16 24 11 11 16.5 17 7 7 17 11 8 8 17 .5 9 7 7 18 7 3 3 ie.5 3 19 -l<.l . 'i -20 -20 . 5 -21 1 21.5 22 22 . 5 23 23 . 5 24 24 . 5 25 25.5 26 26 .'., 27 27. ~-~t\

28.~ - - -'rota; 100 50 50

·-°'l.le1glit. 3600 1800

- 106 -APPENDIX VI (Continued)

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GENERAL INFORMATION TAGGING

Tagging Team 1

Experiment No, : 16 Serial No,

Day-Month-Year: 23.10.69 Condition of fish

Start 30001 A B

Position: 56° 05 1 North latitude 1st hour 30001-30400 26 07° 15 1 East longitude

Statistical rectangle: 1136 2nd hour 30401-30800 33

Surface temperature: 12.9 3rd hour 30801-31000 17

Bottom temperature: 13,0

4th hour Wind force: 15

Wind direction: 18 5th hour

Sea state: 2

Current: N ½ knot 6th hour

Start of tagging: 1500 Total tagged 1000 76

End of tagging: 1730 Tagging Team 2

Serial No , Condition of fish

Notes: 5 tons caught. 21 hours from catch to tagging. Start 29001 A B

let hour 29001-29400 28

2nd hour 29401-29800 29

3rd hour 29801-30000 13

4th hour

5th hour

6th hour

Total tagged 1000 70

No, of B-condition fish in experiment, per mille I 73

SAMPLING

Length to Length composition Age composition of sample 2 ¼ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11,5 12 12,5 13 13,5 14 la.~ 4 15 9 2 i 15.5 15 12 12 16 24 12 12 16.5 17 11 11 17 11 5 5 17.5 9 5 5 18 7 2 2 10.5 3 1 1 19 -19.5 -20 -20.5 -21 1 21.5 22 22.5 23 23.5 24 24,5 25 25.5 26 26.5 27 27.5 28 28,5

Total 100 50 50

Weight 3600 1750

APPENDIX VI (Cont i nued) - 107 -

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

C8NERAL INFORMATION TAGGING

Tagging Team 1

Experiment No. : 17 Serial No,

Day-Month-Year : 24.10.69 Condition of fish

Start 31001 A B

Position: 55° 28 1 North latitude 1st hour 31001-31400 35 06° 531 EaRt longitude

Statistical rectangle: 0935 2nd hour 31401-31700 22

Surface temperature: 13.2 3rd hour 31701-32000 32

Bottom temperature: 13. 4

4th hour Wi!ld force: 20

Wind direction: 27 5th hour Sea state: 3 Current : 6th hour

Start of tagging: 0800 Total tagged 1000 89

End of tagging: 1100 Tagging Team 2

Serial No , Condition of fish

Notes: 5 tons caught. 38 hours from catch to tagging. Start 32001 A B

1st hour 32001-32400 33

2nd hour 32401-32700 25

3rd hour 32701-33000 27

4th hour

5th hour 1

6th hour

Total tagged 1000 85

No, of B-condition fish in experiment, per mille I 87

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12.5 13 13,5 14 u .~ 4 l. l 15 9 4 4 15 . 5 15 9 9 16 24 10 10 16 . 5 17 11 11 17 11 8 8 17 . 5 9 4 4 18 7 2 2 10 . 5 3 1 1 19 -19 ,5 -20 -20. s -21 1 21. 5 22 22. 5 23 23. 5 24 24 -~ 25 25 . 5 26 26 . 5 27 27 . 'J 20 28 . 1

1fotal 100 50 50

Weight 3600 1750

APPENDIX VI (Continued) - 108 -

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GBNERAL I NFORMATION TAGGING

Tagging Team l

Experiment No.: 18 Se r ial No .

Day-Month-Year: 26. 11. 69 Condition of fish

Start 33001 A r,

Pos it ion: 56° 40 1 North lat itude 1st hour 33001-33400 28 06° 32 1 East l ongitude

Statistical rectangle : 1235 2nd hour 33401-33800 29

Surface temperature: 9.45 3rd hour 33801-34000 16 Bottom temperature: 9.8

4th hour 35501-35900 31 Wind force: 5

Wind direction: 4 5th hour 35901-36000 6 Sea state : 2

Current: NE o. 2 knot 6th hour

Start of tagging: Total tagged 1500 110 1715

End of tagging: 2130 Tagging Team 2

Serial No. Condition of fish

Notes: 1 ton caught. Start 34001 A B

1st hour 34001-34400 35

2nd hour 34401-34800 29

3rd hour 34801-35000 15

4th hour 35001-35400 32

5th hour 35401-35500 8

6th hour

Total tagged 1500 119

No , of B- condit ion fi sh in exper iment , per mille I 76

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11 . 5 12 12 . 5 13 13 . 5 14 14 . 5 15 15, 5 2 1 1 16 9 4 4 16. 5 13 12 12 17 28 14 14 17. 5 ' 23 13 13 18 18 4 4 HJ, 5 5 1 1 19 - 1 1 l ll . 'i 1 20 -20. 5 -21 -21. 5 -22 1 22, 5 23 23. 5 24 24, 5 25 25 . 5 26 26 . 5 27 27 . 5 28 28 , 5

Total 100 50 50

Weight 4100 1900

- 109 -

APPENDIX VI (Cont inued)

188S Bl,0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

Giiifr:RA l. nwom:A1'10N ~•AGGING

Tae-ei ng 'l1c am l

:~xpC'rim£'nt. J:i...1.: 19 Serial Ho .

Day-Nonth-Ye-o.:.·: 11. 12.69 Condition of fi sh

Start 36001 A B

Pos ition : 55° OG I North latitude 1st hour 36001-36400 46 04° 34 I EaRt longitude

Statistical rectangle: 0933 2nd hour 36401-36700 35

Surface temperature: 8.2 3rd hour 36701-37000 36 Bottom temperature: 8.4

4th hour Wind force: 14

Wind direction: 225 5th hour Sea state: 2-3

Current: 0 6th hour

Start of tagging: 2000 Total tagged 1000 117

End of tagging: 2300 Tagging Team 2

Serial No . Condition of fish

Notes: 42 tons caught . Start 37001 A B

1st hour 37001-37400 45

2nd hour 37401 -37700 31

3rd hour 37701-38000 27

4th hour

5th hour

6th hour

Total tagged 1000 103

No. of B-condition fish in experiment , per mill~ I 110

SAMPLING

Length to Le:·,gth composition ne<: .;on.po~1.t.1on ,,, san.;pl0 2 ½ cm. below Sample l - deep frozen Sample 2 0 I II+

11.5 12 12.5 13 13.5 14 14 . ', 1, 15,5 16 16. 5 1 17 -17,5 -18 -10. 5 -19 -1\1 , ', -20 l 20.5 -21 2 2 2 21. 5 - - -22 r, - -22.5 7 5 5 23 16 8 8 23,',I 22 12 12 24 18 12 12 24., 1; 1:\ 5 5 25 !l

,, •1

25.5 2 2 2 26 -26.5 -27 1 27. 5 28 20.5 - ., . . ·- -'I1otc1J 100 50 50

f-- ·- ----- - -I 0,.ic: :;t ~ 10250 5150

- 110 -APPENDIX VI (Continued)

ICES BWDEN TAGGING EXPERIM!sNT - TAGGING AND SAMPLING

GENERAL INFORMA1'ION TAGGING

Tagging Team 1

Experiment No.: 20 Serial No,

Day-Month-Year: 7 .1. 70 Condition of fish

Sta.rt 38001 A B

Position: 55° 05 1 North lat i tude 1st hour 38001-38400 37 04° 23' East longitude

Statistical rectangle: 0933 2nd hour 38401-38700 24

Surface temperature: 6.3 3rd hour 38701-39000 23 Bottom temperature: 6.1

4th hour Wind force: 03

Wind direction: 09 5th hour Sea state: 1

Current: 0 6th hour

Start of tagging: 1500 Total tagged 1000 84

End of tagging: 1800 Tagging Team 2

Serial No. Condition of fish

Notes: 8 tons caught . Start 39001 A B

1st hour 39001-39400 45

2nd hour 39401-39700 30

3rd hour 39701-40000 23

4th hour

5th hour

6th hour

Total tagged 1000 98

No. of B-condition fish in experiment, per mille I 91

SAMPLING

Length to Longth composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12, 5 13 13. 5 14 14, 5 15 15.5 16 16. 5 17 17.5 18 Hl,5 19 19,5 20 2 3 3 20. 5 4 2 2 21 11 4 4 21.5 14 4 4 22 15 8 8 22.5 12 8 8 23 12 8 8 23.5 12 5 5 24 11 6 6 24.5 7 1 1 25 25 . 5

1 l

26 26 . 5 27 27 , J 28 28 , 5

Total 100 50 50 Weight 9000 4600

-111 -APPENDIX VI (Contlnued)

ICl•:t; Hl,0IlllN TAGGING EXPERIMENT - TAGGING AND SAMPLING

Gl•:NJ,:RAJ. INl'0RJI\ATION TAGGING

Tagging Team 1

Expt?riment No . : 21 Serial No ,

Day- Month-Year: 8. l. 70 Condi tion ol' f i sh

Start 40001 I, D

Position: 540 32 I North latitude 1st hour 40001-40400 40 04° 27 I };aRt longitude

Statistical rec tangle: 0833 2nd hour 40401-40700 28

Surface temperature: 6.0 3rd hour 40701-41000 30 Bottom temperature: 6.0

4th hour Wind force: 19

Wind direction, 04 5th hour Sea state: 2-3

Current: 0 6th hour

Start of tagging: 1230 Total tagged 1000 98

End of tagging: 1530 Tagging Team 2

Serial No. Condition of f ish

Notes: 2 tons caught. Start 41001 A B

1st hour 41001-41400 43

2nd hour 41401-41700 31

3rd hour 41701-42000 28

4th hour

5th hour

6th hour

Total tagged 1000 102

No, of B-condition fish in experiment, per mille I 100

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12.5 13 13.5 14 u.~ 15 15 , 5 16 16 . 5 17 17 . 5 18 10 . 5 19 19 , 5 20 1 2 2 20.5 4 1 1 21 11 5 5 21.5 12 4 4 22 15 7 7 22.5 7 9 9 23 12 8 8 23.5 12 5 5 24 8 5 5 24. 5 12 1 1 25 4 ~ 2 25. 5 - - -26 - - -26 , 5 1 - -27 1 1 1 27 , 5 28 28 . 5

-Total 100 50 50

Weight 9200 4600

- 112 -APPENDIX VI (Con·tinued)

ICES HLL'DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GBNERA L INFORNJ\ 1'ION TAGGING

Tagging Team 1

Experiment No.: 22 Serial No,

Day-Month-Year: 13.1.70 Condition of fish

Start 42001 A B

Position: 54° 29 1 North latitude 1st hour 42001-42400 46 06° 12 1 East longitude

Statistical rectangle: 0735 2nd hour 42401-42700 34

Surface temperature: 5.2 3rd hour· 42701-43000 35 Bottom temperature: 4.8

4th hour Wind force: 07

Wind direction: 04 5th hour Sea state: 2

Current: NE ½ knot 6th hour

Start of tagging: 0830 Total tagged 1000 115

End of tagging: 1130 Tagging Team 2

Serial No, Condition of fish

Notes: 3 tons caught. 14 hours from catch to tagging. Start 43001 A B

1st hour 43001-43400 48

2nd hour 43401-43700 30

3rd hour 43701-44000 29

4th hour

5th hour

6th hour

Total tagged 1000 107

No , of D-condition fish in experiment, per mille I 111

SAMPLING

Length to Length composition Age composition of sample 2 .1. cm. below 2 SaJDple 1 - deep frozen Sample 2 0 I II+

11. 5 12 12. 5 13 13. 5 14 14,5 15 15.5 16 16.5 17 17.5 18 10.5 19 1 19.5 -20 -20.5 1 2 2 21 4 2 2 21.5 6 4 4 22 12 5 5 22.5 16 6 6 23 17 10 10 23.5 19 8 8 24 14 6 6 24. ~ 8 5 5 25 2 2 2 25 . 5 26 26 . 5 27 27 . 'j 28 28 , 5

Total 100 50 50

Weight 8900 4400

-113 -APPENDIX VI (Cont i nued)

\Cl•::: Hl,l'Dr:N 'I'AGGING EXPERIMENT - TAGGI NG AND SAMPLING

Gl!N1':RAL rnroRMAn0N TAGGING

Tagging Team 1

:-:x perime nt Nt..'.: 23 Serial No .

foy-Month- l' ~nr: 13. 1. 70 Condition of fish

Start 44001 A B

Fosition: 54° 431 North latitude 1st hour 44001-44300 21 06° 31 1 East longitude

Gtatistical rectangle: 0835 2nd hour

Surface temperature: 5 . 0 3rd hour Bottom temperature: 4.8

4th hour Wind force : 08

Wind direction: 04 5th hour Sea state: 2

Current: 6th hour

Start of tagging: 1500 Total tagged 300 21

End of tagging: 1600 Tagging Team 2

Serial No . Condition of fish

Notes: 0. 4 ton caught. Start 45001 A B

1st hour 45001 -45300 34

2nd hour

3rd hour

4th hour

5th hour

6t h hour

Tot al tagged 300 34

No, of B-condition fish in experiment, per mille I 92

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sampl e 2 0 I II+

11. 5 12 12, 5 13 13. 5 14 14, 5 15 15.5 16 16 . 5 17 17 . 5 18 1 10.5 -19 -1.9,'i -20 1 1 1 20.5 4 - -21 4 2 2 21.5 8 3 3 22 12 6 6 22.5 7 5 5 23 17 9 9 23.5 13 8 8 24 14 6 6 24,5 8 5 5 25 5 3 3 25. 5 4 2 2 26 1 26. 5 -27 -27, 5 -28 -28 ,5 1

Total 100 50 50

Weight 8900 4500

- 114 -APPENDIX VI (Coni.inued)

ICES Ill ,0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GENERAL INFORMATION TAGGING

Tagging Team 1

l::xperiment No.: 24 Serial No,

Day-Month-Year: 13.1.70 Condition of fish

Start 44301 A B

Position: 54 O 45 I North latitude 1st hour 44301-44700 28 06 o 34 1 East longitude

Statistical rectangle: 0835 2nd hour 44701-45000 22

Surface temperature: 4.8 3rd hour 46001-46400 23 Bottom temperature: 4.4

15 min 4th hour 46401-46500 5

Wind force: 07

Wind direction: 04 5th hour Sea state: 2

Current: 6th hour

Start of tagging: 1745 Total tagged 1200 78

End of tagging: 2100 Tagging Team 2

Serial No . Condition of fish

Notes : 70 tons caught. Start 45301 A B

1st hour 45301-45700 38

2nd hour 45701-46000 21

3rd hour 46501-46900 28

15 min 4th hour 46901-47000 5

5th hour

6th hour

Total tagged 1200 92

No. of B-condition fish in experiment, per mille I 71

SAMPLING

Length to Length composition Age composition of sample 2 ½cm.below Sample l - deep frozen Sample 2 0 I II+

11.5 12 12 . 5 13 13 . 5 14 \A . 5 15 15.5 1 16 5 1 1 16.5 6 4 4 17 9 5 5 17.5 10 7 7 16 18 7 7 Hl,5 9 5 5 19 7 4 4 19 . S 3 2 2 20 3 4 2 2 20.5 3 2 2 21 6 1 1 21.5 6 1 1 22 2 l 1 22.5 1 - -23 3 2 2 23.5 3 1 l 24 2 2 2 24,5 2 - -25 l l .L

25 . 5 26 26 . 5 27 27 . 5 26 26 , 5

Total 100 50 37 13 Weight 5200 2500 --

- 115 -APPENDIX VI (Continued)

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

Gb:NERAL INFORMATION TAGGING

Tagging Team 1

Experiment No , : 25 Serial No,

Day-Month-Year: 11. 2. 70 Condition of fish

Start 47001 A B

Position : 54o 12 1 North latitude 1st hour 47001-47400 29 05° 06 1 East longitude

Statistical rectangle: 0734 2nd hour 47401-47700 20

Surface t emperature: 4 . 8 3rd hour 47701-48000 22 Bottom temperature: 4 . 4

4th hour Wind force: 04

Wind direction: 18 5th hour Sea state: 1

Current: 0 6th hour

Start of tagging: 2000 Total tagged 1000 71

End of tagging, Tagging Team 2 2300

Serial No , Condition of fish

Notes: 8 tons caught Start 48001 A B

lat hour 48001-48400 38

2nd hour 48401-48700 21

3rd hour 48701-49000 17

4th hour

5th hour

6th hour

Total tagged 1000 76

No, of B-condition fish in experiment, per mille I 74

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11. 5 12 12,5 13 13, 5 14 14,5 15 15 . 5 1 1 16 1 - -16.5 3 1 1 17 4 4 4 17 . 5 7 7 7

' 18 8 8 8 HJ . 5 7 5 5 19 1 4 3 1 19 , lj .1 2 2 -20 3 4 1 3 20.5 4 3 3 21 4 1 1 21.5 - 2 2 22 2 3 3 22.5 1 1 1 23 2 3 3 23.5 2 1 1 24 24,5 25 25.5 26 26.5 27 27.5 28 28,5

Total 50 50 32 18

Weight 2500 2500

- 116 -APPENDIX VI (Continued)

I CES BL0DEN TAGGI NG EXPERIMENT - TAGGING AND SAMPLING

GENERAL INFORMATION TAGGING

Tagging Team 1

Experiment No, : 26 Serial No,

Day-Month-Year: 12.2.70 Condition of fish

Start 49001 A B

Position: 54° 01 1 North latitude 1st hour 49001-49400 30 04° 54 1 East longitude

Statistical rectangle: 0733 2nd hour 49401-49800 34

Surface temperature : 4. 8 3rd hour 49801-50200 28 Bottom temperature: 4.9

4th hour 50201-50500 18 Wind forc e : 07

Wind direction: 16 5th hour Sea state: 2

Current: 0 6th hour

Start of tagging: 1045 Total tagged 1500 110

End of tagging: 1500 Tagging Team 2

Serial No, Condition of fish

Notes: 2 tons caught Start 50501 A B

1st hour 50501-50900 36

2nd hour 50901-51300 31

3rd hour 51301-51700 34

4th hour 51701-52000 26

5th hour

6th hour

Total tagged 1500 127

No, of B-condit i on fish in experiment, per mille I 79

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11 , 5 12 12 , 5 13 13 . 5 14 14 . 'i 15 15 , 5 16 1 1 1 16 , 5 1 3 3 17 2 5 5 17 , 5 7 6 6 18 6 6 6 lE) . 5 7 7 7 ' 19 8 5 5 1g , c; 1 4 4 20 1 2 2 20 . 5 5 2 2 21 2 1 1 21.5 1 2 2 22 4 3 3 22.5 2 1 1 23 1 1 1 23,5 - 1 1 24 1 24.5 25 25.5 26 26 . 5 27 27, 5 28 28,5

Total 50 50 37 13

Weight 2400 2400

- 117 -APPENDIX VI (Continued)

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GENERAL INFORMATION TAGGING

Tagging Team 1

~~xperiment No . : 27 Serial No ,

Day-Month-Year: 26.2.70 Condition of fish

Start 52001 A B

Position: 54o 41 1 North lat itude 1st hour 52001-52400 20 05° 56 I Ea:st longitude

Statistical rectangle: 0734 2nd hour 52401 - 52700 11

Surface temperature : 4. 4 3rd hour 52701-53000 15 Bottom temperature: 4.2

4th hour Wind force: 05

Wind direction: 04 5th hour Sea state: 1

Current: NE slightly 6th hour

Start of tagging: 1900 Total tagged 1000 46

End of tagging: 2200 Tagging Team 2

Serial No , Condition of fish

Notes : 1 ton caught. Start Exp. Nos . 27, 28 and 29 are from the same catch.

53001 A B

Sample 1 is the same for these experiments. let hour 53001-53400 29

2nd hour 53401-53700 30

3rd hour 53701-54000 21

4th hour

5th hour

6th hour

Total tagged 1000 80

No, of B- condition fish in BXJl!'rimcnt , per mille I 63

SAMPLING

Length to Length composition Age composition of sample 2 ½ cm, below Sample 1 - deep frozen Sample 2 0 I II+

11 . 5 12 12 . 5 13 13.5 14 1 1 1 14. 5 5 - -15 5 2 2 15. 5 7 2 2 16 7 5 5 16 , 5 10 8 8 17 20 8 8 17 . 5 15 9 9 18 13 10 10 18 , 5 6 3 3 19 6 1 1 19 , 5 - -20 l -20,5 - 1 1 21 2 21.5 l 22 1 22,5 23 23.5 24 24 , 5 25 25 . 5 26 26 , 5 27 27 . 5 28 28 , 5

Total 100 50 49 1 Weight 3450 1750

APPENDIX VI (Continued) - 118 -

ICBS DL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GJ•:NERAL INFORMATION TAGGING

Tagging Team 1

llxpe riment No,: 28 Serial No .

Day- Month-Year: 27.2. 70 Condition of fish

Start 54001 A B

Position : 54 ° 41 1 North latitude 1s t hour 54001-54400 31 05 O 56 I Eas t longitude

Statistical r ectangle : 0734 2nd hour 54401-54700 19

Surface tempe rature: 4.4 3rd hour 54701-55000 19 Bot tom temperature: 4.2

4th hour Wind force: 11

Wind direction: 04 5th hour Sea state: 2

Current: NE ½ knot 6th hour

Start of tagging: 0800 Total tagged 1000 69

End of tagging: 1100 Tagging Team 2

Serial No, Condition of fish

Notes: Same catch as for Exp. No. 27. 14 hours from catch to tagging.

Start 55001 A B

1st hour 55001-55400 28

2nd hour 55401-55700 18

3rd hour 55701-56000 23

4th hour

5th hour

6th hour

Total tagged 1000 69

No , of B-condi t i on f i sh in experiment, per mille I 69

SAMPLING

Length to Length composition Age composition of sample 2 ½ om. below Sample l - deep frozen Sample 2 0 I II+

11.5 12 12 , 5 13 13.5 14 1 1 1 111 . <; 5 2 2 15 5 - -15.5 7 4 4 16 7 5 5 16.5 10 6 6 17 20 9 9 17.5 15 9 9 18 13 4 4 10,5 6 4 4 19 6 3 2 1 19 , lj - 2 2 20 1 - -20.5 - - -21 2 - -21.5 1 - -22 1 - -22.5 - -23 1 1 23.5 24 24.5 25 25.5 26 26.5 27 27,5 . 28 28,5

To t al 100 50 46 4

Weight 3450 1800

- 119 -APPENDIX VI (Continued)

ICES BL0DEN TAGGING EXPERIMENT - TAGGING AND SAMPLING

GlcNERAL INFORMATION TAGGING

Tagging Team 1

Experiment No.: 29 Serial No,

Day-Month-Year: 27.2.70 Condition of fish

Start 56001 A B

Posit ion : 54° 41 1 North latitude 1st hour 56001-56400 28 05° 56 1 East longitude

Statistical rectangl e : 0734 2nd hour 56401-56700 23

Surface t emperature: 4.0 3rd hour 56701-57000 28 Bottom temperature : 4. 0

4th hour Wind force : 17

Wind direc tion: 04 5th hour Sea state : 2

Current: NE ½ knot 6th hour

Start of tagging: 1400 Total tagged 1000 79

End of tagging: 1700 Tagging Team 2

Serial No. Condi tion of fish

Notes: Same catch as for Exp. No. 27. Start 57001 A B 20 hours from catch to tagging

1st hour 57001-57400 34

2nd hour 57401-57700 24

3rd hour 57701-58000 20

4th hour

5th hour

6th hour

Total tagged 1000 78

No. of B-condition fish in experiment, per mille I 79

SAMPLING

Length to Length composition Age composition of sample 2 1 cm. below " Sample 1 - deep frozen Sample 2 0 I II+

11.5 12 12 . 5 13 13. 5 14 1 1 1 111.'i 5 2 2 15 5 3 3 15. 5 7 7 7 16 7 5 5 16 . 5 10 5 6 17 20 4 1 17 . 5 15 9 9 18 13 6 6 Hl , 5 6 4 4 19 6 1 1 19 , 5 - 1 1 20 1 - -20. 5 - - -21 2 - -21.5 1 1 1 22 1 1 1 22.5 23 23. 5 24 24,5 25 25.5 26 26.5 27 27.5 28 28,5

Total 100 50 46 4

Weight 3450 1750

- 120 -

APPENDIX VII Tagging mortality experiments

Length Survivors Number dead (cm)

Tagged Untagged Tagged Untagged

Day Day

1 2 3 4 5 Total 1 2 3 4 5 Total

Tagging mortality experiment no. 1A Ship 11Thalassa11

Date 25 July 1969 Type Tanlc Duration 5 days Team

20-27 99 104 1 4 7 2 7 21 1 4 3 4 2 14 r,mge

Total 99 104 1 4 7 2 7 21 1 4 3 4 2 14

Tagging mortality experiment no. lB Ship "Gerda Marie" Date 31 July 1969 Type Tanlc Duration 5 days Team

18.0 . 5 1 3 1

19.0 5 2 . 5 4 5 3

20.0 3 4 5 5 . 5 4 4 1 6

21. 0 10 13 5 . 5 12 21 3 4

22.0 11 9 3 1 . 5 9 12 1 1

. 23. 0 5 2 2 4 . 5 3 2 1

24.0 4 4 . 5 3 1

25.0 3 .5

26.0 1

Total 67 79 ? 17 ? ? 16 33 13 ? ? 18 31 Shed 5

J

- 121 -

APPENDIX VII (Continued)

Length Survivors Number dead (cm)

Tagged Untagged Tagged Untagged

Day Day

1 2 3 4 5 Total 1 2 3 4 5 Total

Tagging mortality experiment no. 2 Ship "Gerda Marie" Date 5 ~eptember 1969 Type Tanlc Duration 5 days Team

12.0 1 4 1 . 5 9 2 11 6

13.0 16 3 7 7 . 5 15 26 7 5

14. 0 11 25 2 3 . 5 5 10 1

15. 0 4 3 .5 2 2

16. 0 2 2 . 5

17.0 .5

18.0 . 5 1

19.0 1 1 .5 1

20 . 0 . 5 1

21. 0 . 5 1

22.0 1 1

Total 68 78 7 9 5 ? 10 32 5 5 4 ? 8 22

Tagging mortality experiment no. 3 Ship "Gerda Marie" Date 9 October 1969 Type Tank Duration 5 days · Team 1

14.0 . 5 1 1

15.0 1 . 5 1 1 1

16,0 2 1 1 1 1 . 5 1 3 1 1 1

17 . 0 2 8 8 8 3 . 5 12 9 2 8 10 2

18 . 0 14 4 9 9 4 . 5 6 6 1 1 2

19.0 9 4 1 1 2 . 5 8 6 1 1 2 2

20.0 3 2 1 . 5 2 1

21.0 1 .5

22.0 1 1 .5 1

Total 62 48 3 1 ? ? 30 34 1 ? ? ? 18 19 Shed 1

- 122 -

APPENDIX VII (Continued)

Length Survivors Number dead (cm)

Tagged Untagged Tagged Untagged

Day Day

1 2 3 4 5 Total 1 2 3 4 5 Total

Tagging mortality experiment no. 3 Ship "Gerda Marie" Date 9 October 1969 Type Tank Duration 5 days Team 2

14.0 1 see see Team 1, Experiment 3, tank . 5 Team 1,

15.0 Experi-.5 2 ment 3,

16.0 tank 1 1 . 5 3 1 4 5

17.0 3 3 3 . 5 7 4 4

18.0 14 2 9 11 .5 9 2 1 5 8

19.0 9 1 4 5 . 5 2 1 1 2

20.0 2 . 5 1 1 1

21. 0 2 1 1 . 5

22.0

Total 55 48 6 2 ? ? 33 41 19 Shed 1

Tagging mortality experiment no. 3 Ship "Gerda Marie" Date 9 October 1969 Type Keep net Duration 5 days Team 1

14.0 • 5 1

15.0 . 5 1 1 2 2 1 1

16.0 1 1 1 1 2 .5 2 1 1 1 1

17.0 5 6 1 2 3 2 1 9 1 1 1 1 1 5 . 5 7 13 1 1 4 1 7 1 2 1 4

18.0 9 17 1 1 2 2 1 7 1 2 2 1 6 . 5 12 10 1 1 1 3 1 1 1 1 4

19.0 9 9 1 1 1 1 1 5 1 1 2 . 5 1 3 1 1 2 1 1 1 3

20.0 4 1 1 1 2 .5 1 1 1 1

21. 0 1 1 .5 1 1

22.0 . 5 1

23.0 1 1 .5

24.0 . 5

25.0 . 5 1 1

Total 50 66 7 5 10 12 5 39 3 6 7 11 5 32

-123 -

APPENDIX VII (Continued)

Length Survivors Number dead (cm)

Tagged Untagged Tagged Untagged

Day Day

1 2 3 4 5 Total 1 2 3 4 5 Total

Tagging mortality experiment no. 3 Ship "Gerda Marie" Date 9 October 1969 Type Keep net Duration 5 days Team 2

15.0 see see Team 1, Experiment 3, . 5 2 Team 1, 1 1 keep net

16.0 2 Experi- 2 2 . 5 1 ment 3, 1 3 2 6

17.0 7 keep net 1 1 3 2 1 8

. 5 1 3 1 4 18.0 7 2 1 2 3 3 11

. 5 6 4 2 4 1 11 19.0 6 1 1 1 1 4

. 5 2 1 1 1 1 4 20.0 1

. 5 1 1 21.0

. 5 22.0

.5

Total 35 66 12 6 12 16 6 52 3 6 7 11 5 32 Shed 1

Tagging mortality experiment no. 4 Ship "Gerda Marie" Date 10 October 1969 Type Tank/keep net Duration 4 days Team 1

15.0 1 1 1 1 . 5 2 1 1

16 . 0 4 5 1 1 . 5 2 7 1 1

17 . 0 6 6 2 2 1 2 3 . 5 14 5 3 2 5 1 1 1 3

18.0 12 10 1 1 1 1 4 1 3 4 . 5 16 19 1 1 1 1

19.0 11 10 1 1 1 2 3 . 5 12 7 2 2 1 2 3

20 . 0 4 5 . 5 2 2

21.0 . 5 1

22 . 0 1

Total 88 77 2 2 4 8 16 1 6 13 20 Shed 1

- 124 -

APPENDIX VII (Continued)

Length Survivors Number dead (cm)

Tagged Untagged Tagged Untagged

Day Day

1 2 3 4 5 Total 1 2 3 4 5 Total

Tagging mortality experiment no. 5 Ship "Gerda Marie" Date 27 November 1969 Type Tank/keep net Duration 3 days Team 1

15.0 1 1 1 . 5 1 4

16.0 7 11 1 . 5 15 20 1

17 . 0 24 25 . 5 20 18

18 . 0 21 12 . 5 8 6

19 . 0 2 1

Total 98 98 1 1 2 1 1

Tagging mortality experiment no. 5 Ship "Gerda Marie" Date 27 November 1969 Type Tank/keep net Duration 4 days Team 2

15.5 see 1 see Team 1, Experiment 5 16.0 6 Team 1, 1

.5 19 Experi- 5 17.0 28 ment 5 1

.5 17 2 18.0 11 2

.5 1 19.0 2

Total 84 5 4 2 1 12 Shed 1

Tagging mortality experiment no. 6 Ship "Gerda Marie" Date 7 January 1970 Type Tank Duration 3 days Team 1

19 .5 1 20 .0 4

. 5 4 1 21. 0 6 6 1 2

. 5 6 10 4 4 22,0 11 14 2

. 5 10 9 2 1 23. 0 12 11 2 3

. 5 11 8 2 24.0 13 12 1

. 5 5 9 1 25. 0 5 5 1

.5 1 26. 0 1

Total 83 91 15 12 Shed 2

APPENDIX VII (Continued)

Length (cm)

Survivors

Tagged Untagged

Tagging mortali~ experiment no. Date 7 January 1970 Duration 3 days

19 . 5 1 see 20.0 2 Team 1,

. 5 3 Experi-21. 0 6 mer.t 6

. 5 7 2!el.O 7

.5 7 23. 0 6

.5 6 24.0 15

. 5 4 25. 0 3

Total 67 91 Shed

6

- 125 -

Nu,nber dead

Tagged

Day

1 2 3

Ship Type Team

4 5 Total

11Ge1·da Marie" Tank 2

2 3

6

3

1 1 6 5 2

1

30 2

Untagged

Day

1 2 3 4 5 Total

see Team 1, Experiment 6

12

APPENDIX VIII Length distributions from industrial herring landings in Denmark

Year/ Year- Length (cm) month class

6. 7 . 0 5 0 5

8. 9. 0 5 0 5

Port: Skagen ICES Sub-division Illa

69 07

10 . 0 5

11, 12, 0 5 0 5

13, 0 5

14. 15. 16. 0 5 0 5 0 5

17. 0 5

2 -

18. 0 5

19. 20. 21. 0 5 0 5 0 5

22. 23. 24. 25. 26. 05 05050505

- 3 4 6 6 17 20 29 8 8 1 1

Total Total Total other weight ages (kg)

108 1967 1968 3 23 56 80 68 84 54 41 29 38 22 20 1 1 - 1

1 - 1 1

2 1 2 1 4 2

521 16

4

14.3

17.0 69 08 1967 1968

69 09 1967 1968 1 -

69 10 1967 1968 - 1

69 11 1967 1968 - 1

69 12 1967 1968

70 01 1967 1968

70 02 1967 1968

70 03 1967 1968

70 04 1967 1968

70 05 1967 1968

70 06 1967 1968

70 07 1967 1968

70 08 1967 1968

70 09 1967 1968

70 10 1967 1968

70 11 1967 1968

70 12 1967 1968

1 4 3 3 - 6 3 6 7 10 13 8 10 2 3 - 1 1 - 1 - 88 1 3 8 14 44 67 112 78 92 75 66 34 20 13 - 1 634

1 -

- 2

- 1

- l

- 1

- 1

1 2

3 -

- 1

- 8

2 -

- 1

3 2

2 2

2 3

- 11

1 2

1 -

1 -

- 1

7 10 20 35 7 3 103 99 70 64 25 6 -1 -

2 9 13 34 47 54 60 53 44 35 47 30 13 6 2 -

4 16 30 33 36 48 65 52 7 3 54 33 26 18 13

19 40 59 101 152 129 113 73 66 61 30 19 11 8 2 2

9 12 21 31 95 112 129 124 101 77 60 22 17 6 1 -

1 2 9 6 20 25 44 50 50 54 36 17 16 8

2 - - 6 7 13 17 12 19 10 5 4

2 3 2 7 16 28 52 74 63 52 48 30 19 10

2 5 4 7 8 12 11 4 9 4 - 4 2 -

261437 1 -

3 2 2 1 -2

-1-423 3-211-3 2 211--2 21 --11--1-1 - 1 -132411 23-11-5 3 2 2 1 5 2 2 5 4 2 2 2 - -- 1-7 1 - - 1

- 1 - 1 - - 1 -5 4 4 2 1113-2 -12--11-815411 1-

1 - - 1 1 1 1 4 3 11 13 2

1 -43 33 -11-

- 1 1

- 3 1 1 1 1

- 3 1 2

- 1

1 -- - -- ---1-2 56 42 -132 1- -1 21 -14453 22 2112 4 9 10 17 6 10 5 - 1 - 1 -

1 -

- 1

1 -

-4311-

34 3 - 11 -2

- 1

1 -- 1

-1111-1---1-

-21221 - 2

1 - 73 522

34 458

19 514

12 903

23 832

27 351

3 112

13 428

2 51

5

28 1 - 33

67 NIL

8

1 11

NIL 15

NIL 6

NIL 11

10 19.0

1 15.5

13.4

18.4

20.6

10. 7

3. 5

11.4

1.8

1. 9

7.0

1 329 17.4

262 7. 6

275 10.4

516 15.1

627 15.6

.... .., "'

APPENDIX vm (Continued)

Year/ Year- Length (cm) month class

7. 8. 9. 10. 11. 12. 13 . 14. 03 05 0,3 05 0 5 0 5 0 5 0 5

-- -- - - --Port: Esbjerg ICES Sub-division IVb

3 2 1

15. 0 5

1

16. 17. 18. 0 5 0 5 0 5

1 3 43 33

19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 05 05 05

46 36 64 66 69 61 50 53 26 22 9 -69 08 1967 1968

69 09 1967 1968

69 10 1967 1968

69 11 1967 1968

69 12 1967 1968

70 01 1967 1968

70 02 1967 1968

70 03 1967 1968

70 04 1967 1968

70 05 1967 1968

70 06 1967 1968

70 07 1967 1968

70 08 1967 1968

70 09 1967 1968

70 10 1967 1968

70 11 1967 1968

70 12 1967 1968

71 01 1967 1968

71 02 1967 1968

71 03 1967 1968

71 04 1967 1968

4 1

11 28

13 27 66 129 134 141 162 187 205 208 171129 73 38 20 7 - 1 - 3 20 59 52 52 66 64 7 5 7 5 36 21 9 3

1 - 1 1 4 33 64 99 71 70 65 70 50

4 3

5 8 34 14

6 13

19 48 2

8 4

1 - - 1 - 1 - - 2 - - 1 - 1 3 7 16 27 44 77 78 99 106 95 75 41

1 - 4 3 - 3 3 7 17 23 27 53 79 110 96 110 114 156 138 148 106 58

-3 -- 4- 54 12 9 2215 2630 73 84 95 93 88 92 58 44 40 17

1 - 2 1

3 1 8 27 26 43 49 74 40

1 1 1 4 4 24 20 17 10 11

2

2

1

1 1

3

1 4

1

1

6

3

1

2

7

2

1

- l

58 55

2

24 16 6 14

27 13 2 2 9 4 2 1

28 12

6 1

1

1 4

20 18

11 15 1 3 1

3 2

3 1

1

5 2

1

1 1

64 47

2 1

1 6 10 12 23 25

5 3 2 5 1 5 7 3 3 1 1 1 1

1 4

2 11 2

19 19

22 19

2 7

2 3

2

3 5

4 8

4

1

45 48

1 1

5 4 11 3

22 24

3 1

13 10 1 4 4

1 3 -

7 9 6 14

20 18 1 4

24 25 1 3 4 6 1 -4 1

3 3

10 12 1 7 11

6 7

1 4

49 42 30 17 7 1 2 1 - - 1 -

5 4 1 3 4 1

13 15 13 13 9 5 4 3 1 -1

25 28 24 29 20 12 4 3 2 -

3 5 2 4 2 3 2 1 1-

13 10 10 12 11 8 6 2 1 -

5 2 8 4 - 2 3 11

1 - 1 2

3

13 12 17 10 10 15 33 31 7 9 5 14

2 3 2

1 - - 1 1 -

13 9 5 2 2 5 1 - - 1 4 1

28 21 20 11 14 20 11 1 6 4 16 17 3 1 118 71 11 23 10 9 5 3 1 - - - 1 -11 -- -- --1-

1 1 - 1

1 2 33 41 -1 13 11 -2 -21-

11 11 4 10 5 9 6 1 1 2 2 -2 -1 -- 1- 1-11

18 16 20 12 9 3 2 - 1 -11 11 -1

9 15 14 9 4 5 1 1 1 1 - 3 11

5 7 3 9 4 5 6 3 1-

1 -

2 1

- 1

1 -

11

Total Total Total other weight ages (kg)

622 73. 6 6 200

1 716 161. 6 535 339 548 70. 2 578 108

23 4.0 40

NIL NIL NIL NIL

94 34.6 750 1 270 42.1

1 296 26 38 24. 6

828 111 21. 4 318 1

36 7.4 102 1

5 1. 3 13

3 4.0 39 15 86 27 .1

164 581 172 40.4 228 218

56 14. 6 73 119

4 6. 7 22 126

3 6.4 30 109 11 36.0 95 943

8 43. 8,

119 1195 5 49. 7

77 1532 7 16.8

51 491

.... "° ...,

APPENDIX Vill (Continued)

Year/ Year- Length (cm) Total Total Total month class other weight

11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. ages (kg) 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5

- - - - - - - - - - -- - - - - - - - - - - -- - - - - - - - -Port: Esbjerg ICES Sub-division IVa NW and IVa NE

70 02 1967 - 1 - 1 2 1.1 (NW) 1968 - 2 3 4 5 10 9 7 7 2 - - l - 50 NIL 70 03 1967 6 9 12 11 6 4 5 3 1 - 57 7.9 (NW) 1968 NIL 19 I ,_. 70 12 1967 3 - - - 2 - 1 - 6 3.7 "' 00

(NE) 1968 - 2 5 9 3 9 3 2 l - 34

Port: Esbjerg ICES Sub-division IVc

70 04 1967 1 - 1 2 - 2 - 2 1 2 - 1 12 4.2 1968 6 2 7 15 12 21 16 7 4 1 91

71 02 1967 NIL 3.2 1968 1 - 1 151

71 03 1967 NIL 2.4 1968 1 - 1 81

71 04 1967 NIL 2.6 1968 1 2 5 - 8 47

- 129 -

APPENDIX IX Bl0den Tagging Experiment: the model by M. Nicholson

Notation

R. J

C .. 1)

N .. 1)

f .. 1)

F

q

M

t

e

n

d

==

==

Marine Laboratory, Aberdeen

observed number of tags recaptured during the jth time interval.

predicted number of tags recaptured in the ith area during the jth time.

number of tags present in the ith area during the jth time.

fishing effort in the ith area during the jth time.

annual fishing mortality coefficient.

catchability coefficient.

annual natural mortality coefficient.

duration of time interval.

easterly migration rate.

northerly migTation rate.

dispersion rate.

Dispersion and migration

The fishing area is represented in the model as a grid of equal sized squares. A good approximation to the Bl0den fishery was obtained using 27 statistical rectangles as clcseribecl in section 4. 1.

Movement across the area was simulated by a. combination of two com -ponents; (a) diffusion radian~- from the point of liberntion and (b) a regular displacement of the centre of diffusion. The radial diffusion was controlled by the dispersion rate cl, and displacement of the centre of diffusion by the parameters e and n which, when positive, corrc::;poncl to migration to the east and north respectively. Negative values of e and n indicate movement to the west and south respectively.

When passing from one time period to the nuxt, a fish may remain in a square or move to one of the eight adjacent squares. The probabilities of moving from one square to another are calculated from

where the area of integration A depends on the relative positions of the squares. For example, when d 0-= 0. 5, o -- 0. 0 and n = 0. 0, the probabilities of moving from the centre square are given below:

- 130 -

0.08 0.12 0.08

0.12 0.20 0.12

0.08 0.12 0.08

By applying this matrix of probabilities to the fish in each square at succes­sive time intervals, the movement of fish across the grid was simulated. The direction and rate of movement was determined by the values of the dis­persion and migration parameters.

In Figure 1 we can see the effects of varying these parameters. The distributions of 100 fish 1, 4, 7 and 10 time periods after release are shown for three sets of values of d, e and n:

(i) d = 0. 5

(ii) d = 0. 5

(iii) d = 0. 5

e

e

e

0.0

0.5

1.0

n = 0. 0 (no migration)

n 0. 5 (north-easterly migration)

n = 1. 0 (pronounced NE migration)

In fact, the dispersion and migration rate was affected mainly by varying the ratios e/d and n/d. Values of d = 0. 5, e = 0. 5 and n = 0. 5 generate almost identical distributions to values of d = 1. 0, e = 1. 0 and n = 1. 0. For this reason, and to reduce the number of variable parameters, the dispersion rate was kept constant at d = 0. 5.

The parameters e, n and d refer to probabilities of moving, and cannot be directly related to physical quantities such as swimming speed. However, the model does require that fish are capable of swimming from one statistical rectangle to an adjacent one in a four-week time period. The distance along a diagonal is 30/2 nautical miles, which requires an average speed of 1. 5 nautical miles per day, which is well within the capabilities of herring.

Emigration

Initially, all boundaries in the model were totally reflecting (i. e. fish were assumed to remain always within the 27 squares). Any fish attempting to pass outwards from a boundary square were simply reflected back into it. However, for the 1967 year-class, this was felt to be unreasonable since this . year-class was moving out of the area during the recapture period, and the model was modified to allow emigration from the fishery.

To simulate emigration, some boundaries were made totally absorbing, and as described in the text three different types of emigration were considered. These were:

(a) all barriers reflecting;

(b) coastal and Dogger barriers reflecting, others absorbing;

(c) all non-coastal barriers absorbing.

At liberation

100

e/d = 0 "td = 0 (no migration)

1 i nterval 8 12 12 20

8 12

5 4 int ervals 6 7

5 7 7

1 3 5 6 1 1 2 4

1 1

5

7 int ervals 5 5

4 5 5

2 3 4 4

2 2 3 3

1 2 2

5

10 int ervals 5 5 4 4 4

3 3 4 4

2 3 3 3

2 3 2

8 12

8

4 3

5 3

6 4

5 3 3 3

5 4

5 4

5 4

4 4

4 4

5 4

5 4

4 4

4 4

4 4

- 131 -

APPENDIX IX, Figure 1

The distributions of 100 fish 1, 4, 7 and 10 time periods after liberation. The distributions from three different sets of dispersion coefficients are shown, demonstrating the effect of increasing the north-easterly migration. All boundaries are reflecting and there is no fishing or natural mortality

e/d=l "ld=l (n-e migration)

7 17 17 7 17 17

3 7 7

9 11

5 7 8 2 3 5 6

1 2 3 , 1

9 13

3 4 7

1 2 3 4

1 2 3

1 1

9 14

3 4 6

1 1 2 4

1 , 2 ,

11

1 0

8

5 2

17

12

8

5

3

20

1 3

9

5

3

e/d = 2 "Id= 2 (strong n-e migration)

5 20 31

3 12 20

1 3 5

11 7 25 2 3 6 16

1 3 9

1 4

1

10 18 31

1 2 3 17

1 9 , 4

2

10 18 32

1 1 3 17

1 9

5

2

- 132 -

No direct use was made of fish leaving the fishery. These simply decreased the numbers of fish present, and hence, in later time periods, the predicted catches.

Recaptures

The predicted number of recaptures from the ith square and jth time period is given by:

N .. X Ft -(M +F )t c .. =

l] (1 _ e t t ) lJ Mt+ Ft

where Ft qf .. lJ

The estimate of Rj, the observed number of recaptures in the jth time period, 27

is r; C .. i=l lJ

Estimation of parameters

The predicted number of recaptures in the jth time period is a function of g, the vector of parameters to be estimated, and we write

27 ~ C .. = C. (a).

i=l lJ J -

The least squares solution for~ is that which minimizes

.... ~2

s = r; L' R. - c. (a) ! . J J - J J

This solution cannot be obtained directly and an iterative procedure, based on a Taylor Series expansion of Cj ~), given by:

gi+l

where IS. -1

was tried. This technique however met with only limited success, and the following procedure was adopted.

Only the parameters e/d and n/d (d = 0. 5), the catchability coefficient q, and the type of emigration were allowed to vary. These formed a 3-dimensional solution space from which a regular lattice of trial solution sets was chosen.

- 133 -

The tag returns predicted by the model for each trial solution set were plotted against time together with the observed tag returns, and the optimal solution set was taken to be that for which there was closest overall agree­ment between the two plots.

Figures 2a and 2b show some of the results obtained with different values of the dispersion and migration parameters and constant catchability coefficient (q = 0. 0025). Each figure shows the observed returns from experiments 2-5 for ten 4-week periods after liberation together with the predicted returns from each of the three emigration models. Figure 2a depicts a south-westerly migration, and Figure 2b a north-easterly migration.

As can be seen there was no real difference between these for the first 5 time periods. For the second 5 time periods, however, the pattern of returns for a north-easterly migration was closest to that of the observed returns. For liberations 2-5 the results from simulating migration to the north-east were better than those from all other directions of migration.

As expected, easing the restrictions on emigration reduced the numbers caught in later time periods, although the effect was not great. From Figure 2b, the model with absorption at all non-coastal barriers provided the best overall fit.

Figure 2c shows the results produced by different values of the catcha­bility coefficient, simulating a north-easterly migration and all non-coastal barriers absorbing. From this figure a value of q = 0. 0025 was thought to give the best overall fit.

Simulations of the recaptures of the 1968 year-class from liberations 15-17 were also made. These and the results on the 1967 year-class are discussed in Section 4. 2. Figure 3a shows the results using the best choice of parameters where the overall migration is to the south-west. Figure 3b shows the simulation when the migration is directed to the north-east and the lack of fit contrasts with that for the 1967 year-class.

Although this procedure was very time-consuming (over 200 lattice points were examined), it was possible to span a wide area of the solution space and identify the optimal solutions with some confidence.

V,

C1J L­:::,

800

700

600

50 0

~ 400 c:J u C1J L-

15 300

.._ ClJ

..c

5 20 0 :;z:

100

- 134 -

__ , ' '\

' ' ' ·. ----.

1 2 3 4 5 6 7 8 g

Number of time intervals

APPENDIX IX Figure 2a Liberations 2-5, 1967 year-class. Observed and predicted

recaptures under the assumption of south-westerly migra -tion and constant q.

--··­ ..

10

Cl) QJ

'­:::>

BOO

100

600

500

°6. 400 C, u QJ

'-

~ 300

'­QJ

.Cl

g 200 z:

100

APPENDIX IX

- 135 -

Observed recaptures Predicted re captures

Predicted

Predicted

recaptures

recaptures

Number of time intervals

Figure 2b Liberations 2-5, 1967 year-class. Observed and predicted recaptures under the assumption of north-easterly migra -tion and constant q.

BOO

7 00

600

(/)

OJ 500 L-:::, .... a. c:, u C1' L- 400 -0

L-C1' .c

; 300 z:

2 00

1 00

' ' ' · ' I '

APPENDIX IX

- 136 -

Observed recaptures q =0·0020 q=0·00225 q:0·0025 q:0·00275

Number of time intervals

Figure 2c Liberations 2-5, 1967 year-class. Observed and predicted recaptures for various assumptions of q with simulated north-easterly migration and only coastal boundaries reflecting.

(/1

(1) L­:::> ..... C. Cl u

200

~ 100

(a)

• I\

' . . . ' .

I

I

- 137 -

Observed

Predicted

0 L-_ _j__ _ ___J,ii::__L_ _ __l___-1 __ ...L,_ _ _L _ _____JL...----'----___._--~~

200

(/1

(1) L-

:::> ..... a. Cl u (1)

0:: 10 0

(b)

., .. ~,-- .............. ---------

Time intervals APPENDJX 1X Figure 3 Liberations 15-17, 1968 year-class. Observed and predicted

recaptures under the assumption of (a) south-westerly, (b) north-easterly migration, q = 0. 0025 and only coastal boundaries reflecting.