Report of the Working Group on Redfish Surveys (WGRS) Reports/Expert Group Report/SSGESS… · In...

ICES WGRS - AUGUST REPORT 2013 SCICOM STEERING GROUP ON ECOSYSTEM SURVEYS SCIENCE AND TECHNOLOGY

ICES CM 2013/SSGESST:14

REF. SCICOM, ACOM, NWWG

Report of the Working Group on Redfish Surveys (WGRS)

6-8 August 2013

Hamburg, Germany

International Council for the Exploration of the Sea Conseil International pour l’Exploration de la Mer

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ICES. 2013. Report of the Working Group on Redfish Surveys (WGRS), 6-8 August 2013, Hamburg, Germany. ICES CM 2013/SSGESST:14. 56 pp.

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The document is a report of an Expert Group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the views of the Council.

© 2013 International Council for the Exploration of the Sea

ICES WGRS - AUGUST REPORT 2013 | i

Contents

Executive Summary ........................................................................................................... 1

1 Introduction .................................................................................................................... 2

1.1 Terms of Reference ............................................................................................... 2 1.2 Participants ............................................................................................................ 2

2 Report on the international trawl-acoustic survey on pelagic redfish in the Irminger Sea and adjacent waters in June/July 2013 ........................................ 3

2.1 Historical development of the survey ................................................................ 3

2.2 Material and methods .......................................................................................... 6 2.2.1 Vessels, timing and survey area............................................................. 6 2.2.2 Acoustic assessment ................................................................................ 7 2.2.3 Abundance estimation by the trawl method........................................ 9 2.2.4 Biological sampling ............................................................................... 10 2.2.5 Hydrographic measurements .............................................................. 11

2.3 Results .................................................................................................................. 11 2.3.1 Abundance estimation by the trawl method...................................... 11 2.3.2 Biological data ........................................................................................ 12 2.3.3 Hydrography .......................................................................................... 13

2.4 Discussion ............................................................................................................ 14 2.4.1 Acoustic assessment .............................................................................. 14 2.4.2 Abundance estimation by the trawl method...................................... 15 2.4.3 Biology ..................................................................................................... 16 2.4.4 Hydrography .......................................................................................... 16

3 Future of the survey and participation .................................................................... 18

4 Acknowledgements ..................................................................................................... 19

5 References ..................................................................................................................... 20

Annex 1: List of participants............................................................................................... 50

Annex 2: Agenda of the meeting ....................................................................................... 51

Annex 3: Regression models used in biomass calculations.......................................... 53

Annex 4: WGIDEEPS Terms of Reference for the 2014 and 2015 meetings (draft, not finalized) .................................................................................................... 54

Annex 5: Recommendations ............................................................................................... 56

ICES WGRS - AUGUST REPORT 2013 1

Executive Summary

A trawl-acoustic survey on pelagic redfish (Sebastes mentella) in the Irminger Sea and adjacent waters was carried out by Iceland, Russia and Germany in June/July 2013. About 340 000 NM2 were covered. As relative survey indices, a total biomass of 91 000 t was estimated at depths shallower than the “deep scattering layer” (DSL) by hydroacoustic measurements, about 213 000 t within the DSL shallower than 500 m by a trawl method, and 401 000 t deeper than 500 m by the trawl method. In the shal-lower layer (both acoustic and trawl method), the highest concentrations of redfish were found southeast and south of Cape Farewell. In the layer deeper than 500 m, highest concentrations were found in the northeastern survey area. The estimated biomass and abundance of redfish within the DSL shallower than 500 m and deeper than 500 m derived from the trawl data, however, is considered highly uncertain be-cause of the large error involved in the estimation.

Although the estimates divided by depth layers are not strictly comparable between years as a result of changes in the depth range covered in the deeper layer over the time-series, the total estimates of the whole water column combined can be compared between years. The total relative biomass value of 705 000 t derived in 2013, encom-passing the shallower and the deeper layer is about 200 000 t lower than recorded in 2011. The distribution of redfish was mostly covered except in small parts of the southeast survey area which may result in a small underestimation of the redfish abundance.

The Working Group on Redfish Surveys (WGRS) recommends that the survey should be continued, that it should be carried out every second year, that as many vessels as possible should participate to improve the quality of the derived estimates, and that the timing of the survey should be kept in June/July. The Group recommends that further nations should participate in the next surveys and that chartering of addition-al vessels and cost share should be considered as alternative to direct participation

2 ICES WGRS - AUGUST REPORT 2013

1 Introduction

1.1 Terms of Reference

According to 2011/2/SSGESST11 Working Group on Redfish Surveys (WGRS), Chaired by Kristjan Kristinsson, Iceland and Benjamin Planque, Norway, and met at ICES Headquarters, Copenhagen, from 29-31 January 2013 and in Hamburg, Germa-ny, from 6–8 August 2013 to:

a ) At the February meeting, plan:

i ) a joint international trawl/acoustic survey on the redfish stock in the Norwegian Sea and adjacent waters in August 2013.

ii ) a joint international trawl/acoustic survey on the redfish stocks in the Irminger Sea and adjacent waters in June/July 2013.

b ) At the August meeting, report on the outcome of the 2013 Irminger Sea survey;

WGRS will report by 15 March 2013 (January meeting) and 1 September 2013 (August meeting) for the attention of the SCICOM and ACOM.”

1.2 Participants

Alexey Astakhov Russia Matthias Bernreuther Germany Eckhard Bethke Germany Kristján Kristinsson (Chair) Iceland Alexey Rolskiy Russia

Detailed contact information of the participants is given in Annex 1.

The attendance and expertise in the Group was adequate for addressing the Terms of Reference, as all cruise leaders and specialists on biology and hydroacoustics were present.


2 Report on the international trawl-acoustic survey on pelagic redfish in the Irminger Sea and adjacent waters in June/July 2013

2.1 Historical development of the survey

Several acoustic surveys have been conducted on pelagic redfish in the Irminger Sea and adjacent waters. During the period of commercial fishery in the area, which commenced in 1982, the former Soviet Union, and later Russia, carried out acoustic surveys annually until 1993. These surveys provided valuable information on the distribution and relative abundance of oceanic redfish and on the biology of the spe-cies as well as on the oceanographic conditions of the area surveyed (e.g. Shibanov et al., 1996b). The acoustic measurements were, however, not considered sufficient for stock assessment purposes (ICES, 1991).

In 1991, Iceland (6–26 June in the field) conducted a national survey on pelagic red-fish with a very limited area coverage of 60 000 NM2 (Magnússon et al., 1992a).

In 1992, Iceland and Russia conducted a joint acoustic survey on oceanic redfish in the Irminger Sea from 26 May–11 July in the field. The results of the survey were pre-sented in Magnússon et al. (1992b). It became obvious from the surveys in 1992 that for an acoustic assessment, two vessels were hardly sufficient to cover the whole area of distribution within a reasonable period (ICES, 1993).

In 1993, Russia conducted a survey in the Irminger Sea in field from 7 June-8 July (Shibanov et al., 1994). Iceland carried out a short survey in September in the same year (ICES, 1994a) with no reliable stock size estimate, since the area coverage was limited.

In 1994, Iceland and Norway carried out a survey with two vessels, covering the main distribution area down to 500 m depth (Magnússon et al., 1994). The vessels were in the field from 24 June-17 July. Approximately 190 000 NM2 were covered, resulting in a stock size estimate of about 2.2 million t or 3.5 billion individuals. Most of the fish was measured in the area east of Cape Farewell. In the report from the survey, the view of the ICES Study Group on Redfish Stocks (ICES, 1994b) that the entire area of distribution could not be covered sufficiently by only two vessels (ICES, 1993), was supported.

In 1995 (25 June-30 July in the field), Russia carried out a single vessel survey for red-fish, covering the main distribution area down to 500 m depth. The stock was esti-mated to be 2.5 million t and 4.1 billion individuals (Shibanov et al., 1996a). As the survey was only covered by one vessel, the NWWG meeting in 1996 (ICES, 1996), considered the results to be unreliable.

In 1996 (19 June – 22 July in the field), Iceland, Germany and Russia carried out the survey in June/July. Approximately 250 000 NM2 were covered. The acoustic assess-ment yielded a stock size of about 1.6 million t or 2.6 billion individuals at depths down to 500 m (Magnússon et al., 1996). This estimate was considered to be an un-derestimation of the stock, due to mixture of the redfish towards depths below 500 m. The oceanic redfish concentrations were densest between 200 and 300 m depth, main-ly within a temperature range of 3.5°C to 5°C. Temperatures recorded during the survey were somewhat higher than observed during previous acoustic surveys.


In 1997 (21 June–21 July in the field), Russia carried out a single vessel survey in June/July, resulting in a stock estimate of 1.2 million t down to 500 m depth (Melni-kov et al., 1998).

In 1999 (18 June–10 July in the field), an international acoustic survey on pelagic red-fish was carried out in the Irminger Sea and adjacent waters, with participation of Iceland, Germany and Russia. The acoustically estimated biomass of the oceanic S. mentella in the upper 500 m of the water column was 0.6 million t (Sigurðsson et al., 1999). The observed decrease in survey abundance compared with the years 1994–1996 was very drastic and exceeded the removed biomass by the fishing fleets. The area covered was the most extensive in the time-series until then, but covered only a portion of the horizontal distribution of the oceanic stock. Therefore, the biomass es-timate was considered as an underestimate. The stock above 500 m was observed more southwesterly and deeper than it had been during former acoustic surveys, and a gradual increase in temperature in the observation area was observed. This was considered to have influenced the distribution pattern of the redfish, as the highest concentrations were found in the colder waters, i.e. southwestern part of the survey area.

During all the surveys until 1999, oceanic redfish was only measured by acoustics down to approximately 500 m depth. Attempts have been made to measure below that depth (see Section 2.2.3), but basically without success in obtaining any reliable stock size estimate. The reason is mainly due to the “deep scattering layer” (DSL), which is a mixture of many vertebrate and invertebrate species (Magnússon, 1996) mixed with redfish. Although several attempts have been made by Russia and Ice-land to map the distribution of pelagic redfish at depths below 500 m (Shibanov et al., 1996a; ICES, 1998; Sigurðsson and Reynisson, 1998), the 1999 survey provided for the first time an estimate on the abundance of the pelagic S. mentella >500 m depth in the order of 0.5 million t. Hydrographic observations indicated that the highest concen-trations of redfish below 500 were associated with eddies and fronts.

In 2001 (19 June–14 July in the field), a trawl-acoustic survey was carried out by Ger-many, Iceland, Russia and Norway. Approximately 420 000 NM2 were covered. The stock size measured with acoustic instruments was assessed to be about 715 000 t at depths down to the DSL (or about 350 m), with redfish having a mean length of 34.6 cm. Highest concentrations of redfish were found in the SW part of the covered sur-vey area. In addition to the acoustic measurements, an attempt was made to estimate the redfish within and below the deep scattering layer with so-called “trawl method” (see Section 2.2.3). This was done by correlating catches and acoustic values at depths between 100 and 450 m. The obtained correlation was used to transfer the trawl data at greater depths to acoustic values then to abundance. A total biomass of approxi-mately 1.1 million t was estimated to be at depths between 0 and 500 m and 1.1 mil-lion t shallower than 500 m depth by the use of the “trawl method”. Deeper than 500 m, the densest concentrations were found in the NE part of the area. The average length of the fish caught deeper than 500 m was 38.3 cm. It was further suggested that the estimated abundance derived from the trawl data should be treated with great caution (ICES, 2002).

The basic area coverage during the recent surveys was determined to be extended from what has previously been used and was defined in ICES (1995). As the results from the surveys in 1999 and 2001 indicated that the covered area did not reach the boundary of the distribution area of pelagic redfish in the acoustic layer, the PGRS in 2003 (ICES, 2003a) felt it was necessary to expand the area both to the south and west.


As the fishery had also changed towards greater depths in later years, it was also considered important to continue expansion of the vertical coverage to assess the stock that is below the acoustic layer (below 500 m depth). The results of that survey were presented in ICES (2003b). Germany, Iceland and Russia participated in the in-ternational survey in May/June 2003 (28 May-30 June in the field). Approximately 405 000 NM2 were covered. A total biomass of less than 100 000 t was estimated at depths between 0 and 500 m and about 700 000 t deeper than 500 m by the use of a standard-ized “trawl method”. The redfish biomass of 100 000 t estimated acoustically down to the deep-scattering layer or about 350 m, with redfish having a mean length of 35.3 cm, was the lowest ever obtained since the beginning of the joint measurements. The highest concentrations of redfish were found around 60°N, east of Cape Farewell. Deeper than 500 m, the densest concentrations were found in the NE part of the area. The estimated abundance derived from the trawl data were considered highly uncer-tain. The results of the 2003 survey were regarded as inconsistent and thus did hardly indicate the actual stock status of pelagic redfish. To which extent seasonal effects contributed to this inconsistency, is unknown (see ICES, 2003b).

The international trawl-acoustic survey on pelagic redfish in June/July 2005 (18 June-18 July in the field) was carried out by Germany, Iceland and Russia (ICES, 2005b). Nearly 400 000 NM2 were covered. A total biomass of 551 000 t was estimated at depths shallower than the “deep scattering layer” (DSL) by hydroacoustic measure-ments, and about 674 000 t within and deeper than the DSL by the “trawl method”. In both depth layers, the highest concentrations of redfish were found in the western and southwestern part of the survey area. Although the estimates divided by depth layers were not comparable between years due to changes in the depth range covered in the deeper layer in the 2005 survey, the total estimates of the shallower and deeper layer combined can be compared between years. The total biomass estimate of 1.2 million t, encompassing the shallower and the deeper layer, represented a value within the range of the 1999 and 2001 estimates. Along with the trawl and acoustic measurements since 1992, hydrographic data had been obtained. The results indicat-ed a relationship between the hydrography and distribution of redfish in the survey area.

The international trawl-acoustic survey in June/July 2007 (23 June – 24 July in the field) was carried out by Iceland and Russia (ICES, 2007b). The usual participation of Germany had to be cancelled due to short-term technical problems of their vessel. The German participant, however, compensated the Russian participant by funding additional days in the field, in order to ensure the complete survey area coverage. Nearly 350 000 NM2 were covered, with only slightly increased distances between hydroacoustic tracks and trawl hauls, compared to previous surveys. As relative sur-vey indices, a total biomass of 372 000 t was estimated at depths shallower than the “deep scattering layer” (DSL) by hydroacoustic measurements, and about 854 000 t within and deeper than the DSL by an experimental “trawl method”. In the shallower layer, the highest concentrations of redfish were found southeast of Cape Farewell and in the southwestern survey area. In the deeper layer, high concentrations were also found southeast of Greenland, but as well in the northeastern survey area. Alt-hough the estimates divided by depth layers are not strictly comparable between years due to changes in the depth range covered in the deeper layer in the 2005 and 2007 surveys, the total estimates of the shallower and deeper layer combined can be compared between years. The total relative biomass value of 1.2 million t derived in 2005 and 2007, encompassing the shallower and the deeper layer, represents a value within the range of the 1999 and 2001 estimates.


The international trawl-acoustic survey in June/July 2009 (11 June – 19 July in the field) was carried out by Iceland and Germany (ICES, 2009c). The usual participation of Russia was cancelled because of a number of reasons not specified. About 360 000 NM2 were covered, with increased distances between hydroacoustic tracks and trawl hauls, compared to previous surveys. As relative survey indices, a total biomass of 108 000 t was estimated at depths shallower than the “deep scattering layer” (DSL) by hydroacoustic measurements, the lowest in the time-series (excluding the 2003 esti-mate). About 278 000 t were estimated within the DSL shallower than 500 m by a trawl method and 458 000 t deeper than 500 m by the trawl method. In the shallower layer (both acoustic and trawl method), the highest concentrations of redfish were found southeast of Cape Farewell. In the layer deeper than 500 m, highest concentra-tions were found in the northeastern survey area and southeast of Cape Farewell. The estimated biomass and abundance of redfish within the DSL shallower than 500 m and deeper than 500 m derived from the trawl data, however, is considered highly uncertain because of the large error involved in the estimation. The total relative bi-omass value of 845 000 t derived in 2009 (to make the 2005 and 2007 estimates compa-rable with other years), encompassing the shallower and the deeper layer, was the lowest value recorded excluding the 2003 estimate.

The international trawl-acoustic survey in June/July 2011 (6 June – 18 July in the field) was carried out by Iceland, Germany and Russia (ICES, 2013). About 343 000 NM2 were covered. As relative survey indices, a total biomass of 123 000 t was estimated at depths shallower than the “deep scattering layer” (DSL) by hydroacoustic measure-ments, about 309 000 t within the DSL shallower than 500 m by a trawl method, and 475 000 t deeper than 500 m by the trawl method. In the shallower layer (both acous-tic and trawl method), the highest concentrations of redfish were found southeast and south of Cape Farewell. In the layer deeper than 500 m, highest concentrations were found in the northeastern survey area. The total relative biomass value of 907,000 t was 62,000 t higher than in 2009.

2.2 Material and methods

The methodology and planning of the survey was discussed and agreed during the WGRS planning meeting in Copenhagen, Denmark, from 29–31 January 2013 (ICES, 2013).

2.2.1 Vessels, timing and survey area

Table 1 describes the extent, coverage and the trawl specification of the survey. The Icelandic part of the survey was carried out by the Marine Research Institute (MRI), Reykjavík, with the RV “Árni Friðriksson” from 11 June to 5 July with 22 days in field. The German part was carried out by the Johann Heinrich von Thünen Institute (vTI), Institute of Sea Fisheries, Hamburg, with the RV “Walther Herwig III” during the period 21 June to 19 July, with 14 days in the field. The Russian part was carried out by PINRO, the Knipovich Polar Research Institute of Marine Fisheries and Oceanography in Murmansk, with the RV “Vilnyus” from 15 June to 29 July, with 24 days in the field.

The vessels covered an area of approximately 340 000 NM2 within the boundaries of about 52°N to 65°N and 26°W to 52°W, on transects 30–60 NM apart (Figure 1). Some of the planned transects (ICES 2013) were altered and rescheduled prior to and dur-ing the survey, mainly due to bad weather and reduced survey time of Iceland and Germany which was related to later departure than planned because the vessels were delayed in the dockyard.


2.2.2 Acoustic assessment

A 38 kHz Simrad EK60 split-beam echosounder was used for the acoustic data collec-tion on RV “Árni Friðriksson” and RV “Vilnyus” whereas on RV “Walther Herwig III“ an EK500 was used, also equipped with a 38 kHz split-beam transducer. Prior to the survey, the acoustic equipment on all vessels was calibrated with the standard sphere method (Foote et al., 1987). The settings of the acoustic equipment used during the survey are given in Table 2. During the survey on board of the Icelandic and German vessels the post-processing system (EchoView V5.0 and V4.9 respectively, Myriax) was used for scrutinising the echograms, whereas FAMAS (a post-processing program developed by TINRO) was used in the Russian vessel. Mean integration values of redfish per 5 NM were used for the calculations.

Earlier investigations (Magnússon et al., 1994; Magnússon et al., 1996; Reynisson and Sigurðsson, 1996) have shown that the acoustic values obtained from oceanic redfish exhibit a clear diurnal variation, due to a different degree of mixing with smaller scat-ter as well as changes in target strength. In order to compensate for these effects to some degree, it was decided to discard the acoustic data obtained during periods of the most pronounced mixing, i.e. during the darkest hours of the night, and to esti-mate the values within the missing sections by interpolation.

In further data processing, the number of fish was calculated for statistical rectangles, the size of which was 1 degree in latitude and 2 degrees in longitude. As the observed length range of redfish in the past acoustic surveys had increased from previous years, a length-based target strength formula of TS = 20 × lg(L) -71.3 dB was used again instead of a constant TS of –40 dB (Reynisson, 1992), as used prior to the 2001 survey for all length groups. This TS-equation gives the same results as –40 dB does for 37 cm redfish and is also equal to –38.3 dB /kg as has previously been used by Russia. The total number of fish within subareas A-F (Figure 2) was then obtained by summation of the individual rectangles. The acoustic results were further divided into the number of individuals and biomass based on the biological samples repre-sentative for each subarea.

For the entire survey area, single-fish echoes from redfish were expected to be detect-able down to 350 m. In order to include all echoes of interest, a low integration threshold was chosen. As shown in Table 2, the integration threshold was set at -80 dB//m3 for echo integration. Based on the depth distribution of redfish observed dur-ing the survey and the expected target strength distribution, the method outlined by Reynisson (1996) was used to estimate the expected bias due to thresholding. The results of the biomass calculations were adjusted accordingly.

2.2.2.1 Noise measurements

The measurements of echosounders can be disturbed by noise and reverberation. Re-verberation consists of echoes reflected from unwanted targets and cannot be avoid-ed. For noise, we distinguish between ambient noise (rain, wind-induced noise, thermal noise) and vessel noise (propeller noise, turbulent flow noise). Ambient noise can also not be avoided, whereas vessel noise can be minimized by constructive measures. The German RV “Walther Herwig III” can only supply noise-free values down to approximately 450 m. In the latter case, the reason is the relatively unfa-vourable location of the transducers. The results of the measurements show that the Icelandic RV “Árni Friðriksson”, optimized for acoustic measurements, can accom-plish practically noise-free measurements down to 950 m and the Russian RV “Vil-nyus” down to 1,100 m under good weather condition.


Whereas noise is always present and influences the echo integration results, echoes of redfish are much more seldom. Therefore already very small noise can prevent the measurements. For the improvement of the signal to noise ratio, a threshold is usual-ly applied. The amplitude of the signal decreases with depth whereas the amplitude of noise increases due to time varied gain. Accurate results can only be obtained by applying a threshold adapted to the analysed depth range. Even if redfish are still visible on the echogram, an accurate measurement may be not possible. The applied threshold preventing the influence of noise is optimized for a depth of 250 m (Bethke, 2004).

2.2.2.2 Echo counting

During the survey, situations can be found in which the redfish appears mixed with other deep-sea species like myctophids etc. Even if scrutinizing is performed accu-rately by setting the limits for echo integration, the integration of reverberation can-not always be avoided. This leads to an overestimation of the redfish density. In those situations, echo counting is clearly the more exact measuring procedure. The proce-dure is described in Bethke (2004). Almost identical values are measured if redfish appears in an undisturbed environment as a single fish. The counting procedure is based on the fact that fish are recognized as single targets according to the parameter settings of the echosounder. If this, as within redfish shoals, is not the case, these data are rejected from counting. This, however, leads to an underestimation of the redfish stock. In situations in which the redfish have to be measured in denser concentra-tions, the echo integration has to be preferred. A switch between both methods may be necessary according to the situation found in the field.

Within bad weather conditions cavitation due to strong movements of the vessel can disturb the measurements (Figure 8). If disturbances appear the disturbed single pings have to be removed manually from the echogram to avoid the integration of large noise signals in bad weather. This, however, is a time consuming work and not always possible with a reasonable effort. In this case echo counting is also the prefer-able method because this kind of noise doesn’t influence the results of counting sig-nificantly. Therefore, the application of echo counting helps to save time especially within bad weather conditions. This method can be performed by the usage of the EchoView post-processing software developed by Myriax (www.echoview.com). Since within the German area redfish was not observed in schools the echo counting was applied on the German vessel without any disadvantages. The counting results were converted into sA values for further processing (Bethke, 2004).

The echosounder EK500 used for scientific work since the middle of the 1980s was replaced by the new Simrad sounder EK60 on the Icelandic vessel. The new sounder can be handled in a more convenient way and is equipped with an improved calibra-tion program, allowing the calibration also under rough weather conditions. The EK500 and EK60 can detect individual targets based on the amplitude and width of the echo. It is no surprise that technological progress leads to advantages in function-ality of equipment. However, this is not the case for the echosounder EK60 with re-gard to the single target detection capability needed for echo counting. In one experiment involving 1000 ensonifications of the same target near or on the transduc-er axis by each echosounder, the number of single-target detections was 932 with the EK500 and 220 with the EK60 (Mark I; Jech et al., 2005). This is not sufficient for echo counting and it is probably not possible to obtain sufficient reliable results for as-sessment work with the EK60/BI60 system. Due to the replacement of the older


EK500 on the Icelandic and Russian vessel the counting method was no longer appli-cable on those vessels.

2.2.3 Abundance estimation by the trawl method

The classic method of continuous echo integration deeper than 350 m (within and deeper than DSL) is applicable only under very specific conditions. Because of the increased influence of the vessel’s noise, as well as the mixing of redfish with various components of the DSL (Magnússon, 1996), this is almost impossible. An additional difficulty is due to the decrease of the effective angle of the transducer beam, espe-cially for single fish registration at great depths. This in particular demands for a lower SV-threshold, down to (-85) – (-90) dB for correct echo integration. For hull-mounted transducers, this may cause problems with noise. Therefore, acoustic esti-mation of redfish with a hull mounted transducer in depths exceeding 350 m is very difficult (Dalen et al., 2003).

As in the surveys in 1999–2011, a "trawl method" was used to calculate abundance of redfish. The method is based on a combination of standardized survey catches and the acoustic data, where the correlation between catch and acoustic values during trawling in the shallower layer is used to obtain acoustic values for the deeper layer, based on catches in the deeper layer. To be able to make the calculations, it was de-cided to carry out hauls at different depth intervals, evenly distributed over the sur-vey area.

Based on the conclusion of WKREDS (ICES, 2009a) and the recommendation of ICES on stock structure of redfish in the Irminger Sea and adjacent waters (the conclusion and the recommendation is not agreed by Russia), the Group decided in the planning meeting (ICES, 2009b) to sample redfish separately above and below 500 m, i.e. to sample redfish as was done in the 1999, 2001 and 2003 surveys. In the 2005 and the 2007 surveys (ICES, 2007a) the trawling was from 350 down to 950 m, i.e. within and deeper than the DSL. The group decided to continue sampling redfish separately above and below 500 m in 2013 (ICES, 2013) as well.

The sampling was carried out as follows (ICES, 2011):

1 ) The depth zones shallower than the DSL, in which redfish could be acous-tically identified. Trawling distance was 4 NM.

2 ) The depth zone shallower than 500 m, in which acoustic redfish registra-tion is hampered by the deep scattering layer. The identification hauls cov-ered the following layer (headrope of the net): from the top of the DSL down to 450m. Trawling distance at each depth layer was 2 nautical miles calculated with GPS.

3 ) The depth zones deeper than 500 m depth. The deep identification hauls covered the following 3 depth layers (headline): 550 m, 700 m, and 850 m. Trawling distance at each depth layer was 2 nautical miles calculated with GPS.

The net used on RV “Árni Friðriksson” and RV “Walther Herwig III” was a Gloria type #1024, with a vertical opening of 45–50 m (Table 1). The net used on RV “Vilny-us” was a Russian pelagic trawl (design 75/448) with a circumference of 448 m and a vertical opening of 47–50 m. Russia was using a mesh opening of 40 mm in the codend, while Iceland and Germany were using a mesh opening of 23 mm in the codends. The trawls used on RV “Árni Friðriksson” and RV “Walther Herwig III” were fitted with multiple codend sampling device: the ‘multisampler’ (Engås et al.,


1997). This allowed for successive sampling at three distinct depth zones within one trawl haul and without ‘contamination’ from one depth to the next and no sampling during shooting or heaving of the trawl. During the survey, the vessels employed a total of 21 type 1 trawl hauls on redfish above the DSL which were acoustically iden-tified, 83 type 2 trawl hauls in the depth range from the top of the DSL down to 450 m and 93 type 3 trawls hauls in the depth range from 550–900 m, which were rela-tively evenly distributed over the survey area (Figure 1). The catches were standard-ized by 1 NM and converted into acoustic values using a linear regression model between catches and acoustic values at depths shallower than the DSL.

A linear regression model between the acoustic values and catches (in kg/NM) of type 1 trawls (shallower than the DSL) was applied to predict the acoustic values for each type 2 and 3 trawl. Because few type 1 trawls were taken in 2013 (11 for RV “Walther Herwig III”, 7 for RV “Árni Friðriksson, and 3 for RV “Vilnyus”), the type 1 trawls from the surveys in 2001, 2003, 2005, 2007, 2009 and 2011 were also used in the regression analysis. This made the total type 1 trawls for Iceland 46 (from the 2005, 2007, 2009, 2011 and 2013 surveys), 45 trawls for Germany (from the 2001, 2005, 2009, 2011 and 2013 surveys), and 24 for Russia (from the 2007, 2011 and 2013 surveys). The results of the geometric mean linear regressions between the acoustic values and the catches recorded shallower than the DSL for each vessel are given in Figure 7 and the models output in Annex 2.

Estimation of redfish distribution by the trawl method for type 2 and 3 trawls was done by conversion of catches (catch in kg per NM) to equivalent acoustic estimates by predicting the sA values using the obtained correlation for each vessel. Further, the obtained sA values were then adjusted for the vertical coverage of the trawls and the depth range of each haul (ΔD/Htr; where ΔD is the difference between maximum and minimum depth of each haul, and Htr is the vertical opening during each tow). The sA value for each trawl (sA tr) is:

sA tr = C * K * KH

where C is the catch in kg per NM of each type 2 and 3 trawl, K is the coefficient of the trawl obtained from the linear regression of type 1 trawls for each vessel (see above and the results in Annex 2), and KH is the width of the depth range towed de-fined as:

KH = (HMAX – HMIN + dHTR) / dHTR

where HMAX and HMIN of the headline of the trawl during the tow and dHTR is mean vertical opening of the trawl. For both vessels dHTR was 50 m. For type 3 trawls HMIN was 550 m and HMAX was 850 m. For type 2 trawls HMAX was 400 or 450 m but HMIN varied and was dependent on the minimum depth of the DSL layer.

Based on the regressions, confidence limits for the estimates were also calculated.

After having calculated the sA values from the catches of each haul, the estimation of the abundance and biomass was calculated using the same target strength equation for redfish (20Lg (L) – 71.3) and the same algorithm as used for the acoustic estima-tion. The area coverage was considered to be the same as for the acoustic results and applied to all subareas.

2.2.4 Biological sampling

Standard biological observations needed for the acoustic assessment were carried out, as decided at the planning meeting (ICES, 2013). In addition, otoliths were col-


lected, and stomach fullness as well as parasite infestation, pigment patches and muscular melanosis were recorded according to an approved method (Bakay and Karasev, 2001). A summary of biological sampling in 2013 is given in Table 3. On se-lected stations genetic sampling was carried out. For this purpose, fin clips or tissue samples of gill filaments were collected from as many fish as possible (randomly sampled) and preserved in alcohol (n ~ 1,086). Otoliths were collected from all the individuals and individual length, weight, sex, maturity, parasites and pigmentation recorded.

2.2.5 Hydrographic measurements

Temperature and salinity measurements were made with CTD probes, usually evenly distributed along the acoustic transects and at the turning points of transects down to approximately 1000 m depth (Figure 1). The hydrographic data at depths of 0, 10, 20, 30, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 m from each CTD station were used in the data analysis. A total of 131 CTD stations were conducted during the survey, with 50 carried out by RV “Árni Friðriksson”, 36 by RV “Walther Herwig III“ and 45 by RV “Vilnyus. Due to the early stage of processing of CTD data, only temperature is included in this report. The Russian long-term hydrographic so-called 3K section (10 standard stations) across Reykjanes Ridge was included in the joint survey and taken on RV “Vilnyus” down to 1000 m or the bottom. For the analysis of interannual variations of temperature, the long-term Russian database and data from the last international survey in 2011 were used.

2.3 Results

Figure 3 shows the average sA values by 5 NM sailed distance along the survey tracks, and the average values within the statistical rectangles are given in Figure 4. As shown in Figures 3 and 4, the boundary of the redfish was reached in all direc-tions except in a small area in the SE parts which may lead to small underestimation of total-stock biomass. The stock abundance estimate of pelagic redfish within the covered area of 340 000 NM2 shallower than the DSL amounts to about 160 million individuals or 91 000 t (Table 4). The abundance disaggregated by length groups is given in Table 14a. Compared to 2011, the biomass in the acoustic layer was estimat-ed to be about 32 000 t lower in 2013 (Table 5). There was a slight increase in biomass in subarea E, but a decrease other subareas. In subareas A-D and F and the biomass was the lowest biomass estimate since the beginning of the time-series. In earlier years (Table 5), the biomass estimates in the shallower layer had decreased sharply from 1994–1999. Values prior to 2005, however, covered depths down to 500 m.

The average depth of the DSL and the corresponding confidence limits are shown in Figure 9, combined for all three vessels. The depth of the layer in which redfish can be detected is, on average, around 50–150 m during the night-time but increases to its maximum between 275 and 325 m around noon. As a consequence, the redfish is hard to detect and measure below those depths.

The diurnal variation in the integrated acoustic values is shown in Figure 10, with minimum sA values during night and maximum values around afternoon.


Figure 5 shows the redfish distribution within the DSL above 500 m, based on the regression between the catches and the measured sA values in the layer shallower than the DSL (Figure 7). The circles indicate converted units of sA. The highest values


(sA up to 8 m2/NM2) were observed in the southeastern area (subarea B) between lati-tudes 59° and 60°.

Figure 6 shows the redfish distribution at depths from 550 m to 900 m. The highest values (sA up to 12 m2/NM2) were observed at latitude of about 61°N in the northeast-ern area.

The abundance estimation by subareas is given in Tables 6 and 8 for within the DSL (shallower than 500 m) and deeper than 500 m, respectively, and disaggregated by length groups in Tables 14b and 14c.

The assessment of the redfish stock distributed shallower than 500 m and within the DSL constituted 213 000 t (0.39 billion individuals; Table 6). Applying the 95% confi-dence level to the data, the biomass estimate ranges from 177 000 to 248 000 t. For comparison, the results of the surveys 2001, 2009 and 2011 are given in Table 7. The estimate is the lowest in the time-series and was about 100 000 t lower than in 2011. In 2001, the majority of fish was caught in subarea D whereas in 2009–2013 the majority was found either in subareas A and B respectively.

The assessment of the redfish stock distributed below 500 m constituted 401 000 t (0.61 billion individuals; Table 8). Applying the 95% confidence level to the data, the biomass estimate ranges from 340 000 to 462 000 t.

For comparison, the results of the surveys 1999–2011 are given in Table 9. As the depth coverage of the deep trawls was changed to 350–950 m in 2005 (ICES, 2005a) and again in 2009 to 500–950, the survey estimates are not strictly comparable be-tween years. The 2005 and 2007 data provide estimates within and deeper than the DSL (350–950 m), whereas the other surveys cover the depth range 500–950 m. The results show that in subareas A and B, the abundance estimate in 2013 decreased compared to 2011 and is the lowest in the time-series. The biomass increased in sub-areas D-F.

There has been a substantial decrease in the biomass in 2009-2013 compared to 1999-2003, when the trawling was done in similar way, especially in subareas A and B, the main fishing areas. The total biomass estimate in 2013 is the lowest in the time-series.

2.3.2 Biological data

2.3.2.1 Sex composition, length and weight

At depths shallower than 500 m, the percentage of males (61.5%) exceeded that of the females (38.5%). The proportion of females has remained stable compared to 2011. In the layer deeper than 500 m, the sex ratio was different, compared to that of the shal-low layer (66.6% males, 33.4% females), and the proportion of females increased by about 7.5%. Fish length in the catches ranged from 26 to 47 cm. The mean length of redfish in the shallower layer was 35.5 cm, and the mean individual weight was 556 g. In the deeper layer, the mean length was 38.5 cm, and the mean weight was 701 g, which is 10 g higher than 2011. In the northeastern (NE) area (Tables 11a and 11b), redfish caught in the shallower layer were on average about 3.3 cm shorter than in the deeper layer. In the southeastern (SE) area (Tables 12a and 12b), redfish from the shallower layer were 1.8 cm shorter than from the deeper layer, whereas in the southwestern (SW) area (Tables 13a and 13b), redfish from the shallower layer were 0.8 cm smaller than redfish from the deeper layer. The length frequencies from the trawl stations are illustrated in Figure 11, and length-disaggregated abundance data are given Tables 14a-c. In depths shallower than 500 m (Figure 11, upper panel), the


peak of the length frequency distribution is around 35.5 cm, which is similar to the 2009 survey. In the layer deeper than 500 m, the length distribution shows a broad maximum around 35–42 cm (Figure 11, lower panel), with a distinctive peak of fish 37 cm in the SW area.

2.3.2.2 Feeding

An overview on the stomach fullness is given in Table 15. In both the shallower and deeper layer, the majority of the redfish stomachs (78% shallow, 73% deep layer) were everted. In total 9% of the investigated redfish from the shallower layer and 5% in the deeper layer had food items in their stomachs. In the shallow and deep pelagic layer, the number of fish with little content was highest (4.7 and 2.8%) with a decreas-ing trend towards high contents. Stomach contents have partly been analysed and the remaining fixed stomachs are being analysed.

2.3.2.3 Maturity

The great majority of the males were identified as maturing, whereas most of the fe-males were in the post-spawning stage, as expected from earlier investigations. Fig-ure 12 displays the maturity ogive by sex and depth layers. In general, around 90% of the females and 100% of the males were identified as being mature at a length of 32 cm, and 50% maturity was reached for females around 29–30 cm (deeper layer).

2.3.2.4 Parasite infestation

Tables 16a and 16b contain the results of the analysis of the infestation of the beaked redfish S. mentella by parasitic copepod Sphyrion lumpi and the occurrence of individ-uals with pigmented patches (black and red spots) on the skin in the survey area. As in previous years, the infestation by copepod S. lumpi and occurrence of pigmented patches on redfish skin was higher in females than in males of S. mentella throughout the whole survey area and at all depths. Above 500 m 56.1% of the females were infested with S. lumpi or were carrying remnants, while the percentage in males was 40.3. Below 500 m the difference in the values of infestation between females and males were less pronounced with 45.5% and 42.7%, respectively. Above 500 m in total 18.8% of the red-fish were carrying black or red pigment patches (females: 22.0%, males: 16.9%), whereas in total only 7.5% (females: 10.5%, males: 6.0%) of the redfish below 500 m were carrying pigment patches. The highest abundance index (No. S. lumpi and, or remnants / No. fish examined) was observed in females above 500 m in the southwestern area with 2.1. The index was equal to or less than 1 for females and males in all areas below 500 m.

2.3.3 Hydrography

During the survey, 131 oceanographic stations, including observations in the long-term hydrographical Russian 3K section, were carried out. Oceanographic investiga-tions were conducted in the area between 52°52'N and 64°45'N and from the Rey-kjanes Ridge westward to 51°W. Temperature data from a similar survey in 2011 were also used for the analysis. The results are shown in Figures 13–20.

Temperature in the surface layer varied from 1.9°С in the western survey area to 9.2°С in the east and south (Figure 13). Positive temperature anomalies were ob-served over a large part of the area. The largest positive anomalies occurred in the Irminger Current (1.5°C) and the Labrador Current (2.0°C). Local areas with negative anomalies of up to -1.5°C were found in the northern and western parts of the survey area. The temperature was colder than during a similar period in 2011 (by up to 1.5-


2.0°C) almost over the entire area, however in the north it was warmer (by up to 1.0°C) (Figure 17).

At 200 m and 400 m, the temperature ranged from 3.5°С to 8.0°С and was 0.3°С - 0.7°С higher than the long-term mean (Figure 14-15). The temperature at these depths decreased by 0.3-0.6°С compared to 2011. The largest decrease occurred in the area of subpolar divergence. Some temperature increase was observed in the Irminger Cur-rent. The temperature at 600 m was on the average higher, but slightly lower than in 2011 (Figure 16).

The data from the section 3K suggested that there was a decrease in temperature compared to 2011 in the northern part of the section (up to 1.5°C), while in the south-ern part the temperature increased by 0.5-1.0°C. The average temperature in the 0-200 m, 50-200 m and 0-500 m layers along the entire section was slightly above the nor-mal (Figure 18-20). The largest positive anomalies (0.2-0.4°С) were registered in a front zone (stations 3-6) in the 200-500 m layer. In the 500-1000 m layer, the tempera-ture was close to average.

Similar temperature conditions in the Irminger Current (stations 7-9) were observed for the 0–200 m layer in 1999 and 2011, 0–500 m in 2005, and 500–1000 m in 2007.

2.4 Discussion

2.4.1 Acoustic assessment

The survey covered 340 000 NM2, which represents most of the distribution area of redfish in the Irminger Sea and adjacent waters. The boundaries of the horizontal dis-tribution were more or less reached in all direction except small part in the SE area. Compared with earlier investigations at this time of the year (Magnusson et al., 1994, 1996; Sigurðsson et al., 1999; ICES, 2002; ICES, 2003b; ICES, 2005b, ICES, 2007b, 2011), the relative distribution of the redfish is similar to the distribution observed in 2001, 2005, 2007, 2009 and 2011. Since the survey in 2003 was carried out about one month earlier as the previous surveys, and a marked seasonal effect was observed, the bio-mass estimates for 2003 were considered as inconsistent (ICES, 2003b). The surveys since 2001 (excluding the survey in 2003) indicate that the redfish were more westerly (and southwesterly) distributed than prior to 2001 when the highest concentration was found SE of Cape Farewell. Since 1994, the results of the acoustic estimate indi-cate a drastically decreasing biomass trend with the lowest value recorded in 2013, excluding the 2003 survey (Table 5). The estimate was in 2013 lower than estimated in 2011.

The present results show that in subareas A and B, where the highest concentration of redfish was observed in the surveys 1994–2001, the biomass in 2013 was about 4% of the 1994 estimates. In subarea D, where highest biomass was found in 2001, but al-most no redfish was recorded in 2009–2013. In subarea E, south and southwest of Cape Farewell, the biomass has decreased compared to the 2005 and 2007 surveys, but was similar as in 2011. The estimated biomass in this area was less than 20% of the estimate in 2005. The increased fraction of fish in the southwestern survey area in 2001, 2005 and 2007 is consistent with an increasing proportion of fishery activities in this area since 2000 (ICES, 2007b).

Although discarding the acoustic data obtained during the times of the most pro-nounced mixing with the scattering layer, the diurnal variation of the integration values was evident. During night-time (i.e. from about 22:00–08:00 GMT), the integra-tion values usually decrease. Compared with the surveys in 1994 and 1996 (Magnús-


son et al., 1994; Magnússon et al., 1996) this is, however, not as pronounced now as it has been.


During Russian trawl-acoustic surveys in 1995 and 1997, attempts were made to as-sess the redfish deeper than 500 m by acoustic methods. According to an expert esti-mation in 1995, the stock constituted nearly 900 000 t (Shibanov et al., 1996a), and in 1997, it was estimated to be 500 000 t (Melnikov et al., 1998). In the joint survey in 1999, an attempt was made to estimate the abundance deeper than 500 m based on a similar method as presented here. About 500 000 t were estimated deeper than 500 m with a high degree of uncertainty (Sigurðsson et al., 1999). From the data obtained during the joint survey in 2001 (ICES, 2002), the biomass of redfish between 0 and 500 m was estimated about 1 075 000 t, and deeper than 500 m about 1 057 000 t. The 2003 estimate was 92 000 t shallower than 500 m and 678 000 t deeper than 500 m (ICES, 2003b). In 2005 and 2007, the total biomass over both layers was about 1.2 million t, with different shares between the depth layers (2005: 551 000 t shallow, 674 000 t deep; 2007: 372 000 t shallow, 854 000 t deep). The total biomass in 2011 was estimat-ed about 907 000 t (123 000 t in acoustic layer, 309 000 t in the DSL above 500 m and 475 000 t below 500 m). The total biomass in 2013 was estimated about 705 000 t (91 000 t in acoustic layer, 213 000 t in the DSL above 500 m and 401 000 t below 500 m). This is a decrease of about 200 000 tonnes compared to 2011 and the lowest estimate since the beginning of the time-series.

The estimates given for the shallower and deeper layer in 2005 and 2007 are not strict-ly comparable with earlier results and the 2009-2013 results, as the depth coverage is different. The estimates within the DSL were combined with the acoustic results in the surveys 1999–2003 to obtain indices for the layer down to 500 m, whereas in 2005 and 2007, the estimates within and deeper than the DSL were combined, allowing an estimation of abundance for the water column from 350–950 m. In 2009-2013, the es-timates were calculated separately for the acoustic data, for the layer within the DSL shallower than 500 m (trawl method) and deeper than 500 m (trawl method). These changes do not allow a direct comparison between the surveys without recalculation of the estimates, but the acoustic and the trawl data can be summed up to obtain the total estimate of abundance and biomass by each area, which is comparable between years.

The quality of the trawl method cannot be verified as the dataseries is relatively short. Such evaluation on the consistency of the method can therefore not be done until more data points are available. Therefore, as has been stated in earlier reports of the PGRS/SGRS, the abundance estimation by the trawl method must only be consid-ered as a rough attempt to measure the abundance within the DSL and deeper than 500 m. In addition, the codend of the trawl was replaced by the multisampler system for the Icelandic trawl in 2009 and for the German trawl in 2011. This may affect the slope of the regression line (Figure 7). It is not possible to obtain reliable results with-out comparing the two trawl system with large number of trawls stations. This can only be done step by step.

Based on the converted sA values derived from the trawl data deeper than 500 m, one can see that although the catch rates are usually low, the distribution area of the red-fish at those depths is very large and exceeds the distribution area of the redfish shal-lower than the DSL. About 46% and 23% of the redfish deeper than 500 m were found in subareas A and B, respectively, with the highest concentrations found in the north-eastern part of subarea A and southeast of Cape Farewell. As in previous years, sub-


areas A and B together contained 70–95% of the biomass in the deeper layers with the lowest value in 2013.

Within the DSL layer shallower than 500 m the main distribution was in subarea B and then in A. The distribution is similar to what was observed with acoustic meas-urements.

2.4.3 Biology

Due to the difference in depth layers observed, compared to 2005 and 2007 when the layers were ‘shallower than’ and ‘within and deeper than the DSL’, the length distri-bution data are not comparable to some of the last surveys. The differences in mean length between the layers <500 m and >500 m in all areas, however, display the pat-tern observed in the commercial fisheries and in surveys prior to 2005, especially in the northeastern area. The relatively high amount of redfish of 33–37 cm length (peak at 35 cm) in the shallow layer of the NE and SE areas have been observed in the sur-vey 2009 and 2011 and coincide with recently observed large numbers of demersal S. mentella on the East Greenland shelf (ICES, 2011b) that are probably partly migrating eastwards into the pelagic waters at that size.

As in previous years, the majority of the fish caught had everted stomachs, and only few stomach content data could be collected, thus the feeding condition and food composition could not be fully evaluated. However, stomach samples were taken and will be analysed accurately. From the observations made so far, redfish are opportun-istic feeders that graze within the DSL (Magnússon, 1996) and feed on invertebrate species and small fish in the layers shallower and deeper than the DSL.

In both depth layers (shallower and deeper than 500 m) maturity of males was reached earlier than that of the females, as seen in earlier surveys. Redfish of both sexes in the shallow layer were mature at similar sizes compared to 2011. The classifi-cation into the various stages by macroscopic analysis, however, is not straightfor-ward and therefore subject to high variation. Further research and training, coupled with histological analyses, is necessary to distinguish between the different stages.

The obtained results show year-to-year value stability for parameters of S. mentella infes-tation by copepod S. lumpi and occurrence of pigmented patches on the redfish skin.

Some differences in redfish infestation between areas and depths were observed. These differences in occurrence of the above characteristics in S. mentella between specific are-as may be associated with the peculiarities of size structure and sex composition of the catch and the ecology of the mesopelagic parasite S. lumpi (Bogovski and Bakay, 1989; Bakay and Melnikov, 2002, 2008). Registered differences (lower at depth of more than 500 m) in occurrence of pigmented patches on skin of individuals by depth may also be associated with the distribution of larger S. mentella individuals (over 40 cm) that demonstrate sharp reduction of pigmented patches occurrence mainly at depth deep-er than 500 m (Bogovski and Bakay, 1989; Bakay and Melnikov, 2002, 2008).

2.4.4 Hydrography

Analysis of oceanographic situation during the survey and long-term data including 2003, allows following conclusions:

Strong positive anomalies of temperature observed in the upper layer of the Irminger Sea with a maximum in 1998 are related to an overall warming of water Irminger Sea and adjacent areas in 1994-2003. These changes were also observed in the Irminger Current above the Reykjanes Ridge (Pedchenko, 2000), off Iceland (Malmberg et al.,


2001) and in the Labrador Seawater (Mortensen and Valdimarsson, 1999). Thus an increase in temperature and salinity has been found in the Irminger Current since 1997 to higher values than for decades, as well as a withdrawal of the Labrador Sea-water due to a slow-down of its formation by winter convection since the extreme year 1988 (ICES, 2001).

The results of the survey in 2003 were confirmed by the presented high water tem-perature anomalies of the 0-200 m layer in the Irminger Sea and adjacent waters. In 200-500 m depth and deeper, positive anomalies in most parts of the observation area were observed, but increasing temperature as compared to the survey in June-July 2001 was obtained only north of 60° N in the flow of the Irminger Current above the Reykjanes Ridge and the northwestern part of the Irminger Sea.

In June/July 2005, the temperature of the water in the shallower layer (0-500 m) of the Irminger Sea was higher than normal (ICES, 2005b). As in the surveys 1999-2003, the redfish were aggregating in the southwestern part of the survey area, partly influ-enced by these hydrographic conditions. In connection with the continuation of posi-tive anomalies of temperature in the survey area, the redfish concentrations were distributed mainly in depths of 450-800 m, within and deeper than the DSL. Favoura-ble conditions for aggregation of redfish in an acoustic layer have been marked only in the southwestern part of the survey area with temperatures between 3.6-4.5°C.

In June/July 2007, again a higher temperature in the shallower layer was observed, as seen since 1996.

Hydrography surveys of June/July 2011 show that the increased temperature back-ground is still in place in the survey area on the level specific for warm and moder-ately warm years. However as compared to the 2007 and 2009 surveys the heat capacity reduction trend is observed.

Hydrography results of the 2013 survey show that the increased temperature situa-tion in recent years is still persisting in upper 600 m depth layer of the survey area indicating warm and moderately warm years. However, compared to the 2011 sur-vey the temperature decreased by 0.3-0.7°C in most of the survey area, with excep-tion of the Irminger current’s waters where the temperature increased up to 0.2-0.4°C.

Decreasing water temperature since 2009 may affect spatial distribution of major con-centrations of the beaked redfish both in horizontal and vertical planes (Pedchenko, 2005). The abundance and distribution of pelagic S. mentella in relation to oceano-graphic conditions were analysed in a special multistage workshop (WKREDOCE1-3). It was established that the spatial distribution of S. mentella in the Irminger Sea mainly in waters < 500 m appears strongly influenced by the Irminger Current Water (ICW) temperature changes, linked to the Subpolar Gyre (SPG) circulation and the North Atlantic Oscillation (NAO). The fish avoid increasing volumes of ICW (>4.5ºC and >34.94) in the northeastern Irminger Sea due to an intensification of the SPG by displacing towards the southwest, to fresher, colder waters. A weakening of the SPG has the opposite effect (ICES, 2012).


3 Future of the survey and participation

The Group confirms its 2005 recommendations (ICES 2005a, 2005b) that the survey should be continued, that it should be carried out every second year, that as many vessels as possible should participate to improve the quality of the derived estimates, and that the timing of the survey should be kept in June/July.

After several unsuccessful attempts by the Group to involve more nations/vessels in the survey (see ICES, 2007a), the possibility of chartering e.g. an Icelandic or Russian vessel, equipped with the necessary gear and instrumentation, was discussed. Similar as in other international surveys (e.g. on Atlanto-Scandian herring and blue whiting), a cost and staff contribution by those nations fishing on the stock could be considered to ensure that at least four vessels could participate in the survey, as recommended by the Group in 2005 (ICES, 2005b). The Group recommends that the ICES Secretariat supports the Group’s efforts to involve further nations in the next surveys. To date, this situation has not improved, but even become more serious:

On two of the last four surveys (2007 and 2009), the redfish distribution area was only covered with a relatively low density of hydroacoustic tracks and trawl hauls by two vessels, due to the cancellation of the German part in 2007 and the Russian part in 2009. The Group would like to express its severe worries about the insufficient survey participation of ICES countries involved in the pelagic redfish fisheries in the Irminger Sea and adjacent waters. The Group is particularly concerned with the de-creased data quality and higher uncertainty (on top of the methodological draw-backs) in the derived dataseries and corresponding low credibility in the Group’s work and consequently the advice on the stock status.

In the January 2013 WGRS meeting, a discussion on the future of WGRS was raised. At present, the aim of WGRS is to coordinate and report on surveys in the Irminger and Norwegian Seas in order to provide data in support to redfish assessment. The use of the data collected is currently limited; it is not incorporated into analytical as-sessments of redfish stocks and does not contribute to ecosystem description or as-sessment. Little additional data is collected on other components of the ecosystem. The support for the survey is limited and the group has reiterated many times its need for additional ship-time and wider international support, without success. The group expressed concerns that the limited scope and use of the data may be a major reason behind this lack of support and that status quo may lead to further decline in institutional support and group participation.

Developments in analytical stock assessment methods in NWWG and AFWG that could incorporate the data collected during the WGRS surveys would raise the pro-file of the surveys. In addition, the working group should explicitly consider data quality and how it contributes to assessment accuracy and precision.

In addition, the surveys planned and conducted under WGRS offer a unique plat-form for the study of the mesopelagic ecosystem of the North Atlantic. The mesope-lagic layer (also referred to as deep scattering layer) is a ubiquitous feature of the world ocean believed to host up to 1 billion tons of mesopelagic fish, in addition to many other animal groups (cephalopods, crustaceans, jellyfish etc.). The ecology of the North Atlantic mesopelagic ecosystem is still largely unknown and fundamental questions concerning the trophic importance of this system for commercial fish spe-cies or for marine mammals, as well as for the retention of material sedimenting for the epipelagic layer is still unanswered. The WGRS work should be broadened to


open towards ecosystem studies of the mesopelagic layer. This would provide sup-port 1) for advice on multiple components of the system (for example, recent inquir-ies on the commercial fishing of mesopelagic fish), 2) for ecological research on the mesopelagic layer and 3) for additional ecological research on redfish (e.g. trophic ecology).

It was suggested that the group should be renamed to reflect these new objectives and that it should build a strategy for developing an ecosystem approach in the com-ing years. By operating these changes, the group would be better structured to meet the objectives of ICES, with regard to advice (Advisory plan: “The scope of advice provided by ICES is broad taking into account exploited and unexploited compo-nents of marine ecosystems”), science (Science Plan section 4.1: Understanding eco-system functioning) and monitoring (Science plan: integration of surveys and observational technologies into operational ecosystem surveys).

4 Acknowledgements

The Group wishes to thank everyone who has been involved in this work, especially to those people conducting the surveys and being responsible for the flexibility and successful logistics during the recent survey. The German part of the survey was partly funded by the European Commission within the Data Collection Framework (Reg. 199/2008).

The meeting was hosted by the Thünen-Institute of Sea Fisheries in Hamburg, Ger-many. Many thanks for their great hospitality and technical organization of the meet-ing.


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ICES. 2011b. Report of the North Western Working Group (NWWG). ICES CM 2011/ACOM:7.

ICES. 2012. Report of the Second Workshop on Redfish and Oceanographic Conditions, 16 - 17 August 2012, Johann Heinrich von Thünen Institute, Hamburg, Germany. ICES CM 2012/ACOM:25. 70 pp.

ICES. 2013. Report of the Working Group on Redfish Surveys (WGRS), 6-8 August 2013, Ham-burg, Germany. ICES CM 2013/SSGESST:14. 37 pp.

Jech, J. M., Foote, K. G., Chu, D. and Hufnagle Jr., L. C. 2005. Comparing two 38-kHz scientific echosounders. ICES Journal of Marine Science, 62: 1168–1179.

Magnússon, J. 1996. The deep scattering layers in the Irminger Sea. Journal of Fish Biology 49 (Suppl. A): 182–191.

Magnússon, J., Magnússon, J. V., and Reynisson, P. 1992a. Report on the Icelandic survey on oceanic redfish in the Irminger Sea, in June 1991. ICES CM 1992/G:64, 11 pp.

Magnússon, J., Magnússon, J. V., Reynisson, P., Hallgrímsson, I., Dorchenkov, A., Pedchenko, A., and Bakay, Y. 1992b. Report on the Icelandic and Russian acoustic surveys on oceanic redfish in the Irminger Sea and adjacent waters, in May/July 1992. ICES CM 1992/G:51, 27 pp.

Magnússon, J., Nedreaas, K. H., Magnússon, J. V., Reynisson, P., and Sigurðsson, T. 1994. Re-port on the joint Icelandic/Norwegian survey on oceanic redfish in the Irminger Sea and adjacent waters, in June/July 1994. ICES CM 1994/G:44, 29 pp.

Magnússon, J., Magnússon, J. V., Sigurðsson, Þ., Reynisson, P., Hammer, C., Bethke, E., Ped-chenko, A., Gavrilov, E., Melnikov, S., Antsilerov, M., and Kiseleva, V. 1996. Report on the Joint Icelandic / German / Russian Survey on Oceanic Redfish in the Irminger Sea and Ad-jacent Waters in June/July 1996. ICES CM 1996/G:8, Ref. H, 27 pp.

Malmberg, S. A., Mortensen, J., and Jónsson, S. 2001. Oceanic fluxes in Icelandic waters. ICES CM 2001/W:08, 14pp.

Melnikov, S. P., Mamylov, V. S., Shibanov, V. N., and Pedchenko, A. P. 1998. Results from the Russian Trawl-acoustic survey on Sebastes mentella stock of the Irminger Sea in 1997. ICES CM 1998/O:12, 15 pp.

Mortensen, J. and Valdimarsson, H. 1999. Thermohaline changes in the Irminger Sea. ICES CM 1999/L:16, 11 pp.

Pedchenko, A. P. 2000. Specification of oceanographic conditions of the Irminger Sea and their influence on the distribution of feeding redfish in 1999. ICES North-Western Working Group 2000, Working Document 22, 13 pp.

Pedchenko, A. P. 2005. The role of interannual environmental variations in the geographic range of spawning and feeding concentrations of redfish Sebastes mentella in the Irminger Sea. ICES Journal of Marine Science 62: 1501–1510.

Reynisson, P. 1992. Target strength measurements of oceanic redfish in the Irminger Sea. ICES CM 1992/B:8, 13 pp.

Reynisson, P. 1996. Evaluation of threshold-induced bias in the integration of single-fish ech-oes. ICES Journal of Marine Science 53: 345–350.


Reynisson, P. and Sigurðsson, T. 1996. Diurnal variation in acoustic intensity and target strength measurements of oceanic redfish (Sebastes mentella) in the Irminger Sea. ICES CM 1996/G:25, 15 pp.

Shibanov, V. N., Bakay, Y. I., Ermolchev, V. A., Ermolchev, M. V., Melnikov, S. P., and Ped-chenko, A. P. 1994. Results of the Russian trawl acoustic survey for Sebastes mentella of the Irminger Sea in 1993. ICES CM 1994/G:34, 20 pp.

Shibanov, V. N., Pedchenko, A. P., Melnikov, S. P., Mamylov, S. V., and Polishchuk, M. I. 1996a. Assessment and distribution of the oceanic-type redfish, Sebastes mentella, in the Irminger Sea in 1995. ICES CM 1996/G:44, 21 pp.

Shibanov, V. N., Melnikov, S. P., and Pedchenko, A. P. 1996b. Dynamics of commercial stock of oceanic-type redfish Sebastes mentella in the Irminger Sea in 1989–1995 from results of Rus-sian summer trawl-acoustic surveys. ICES CM 1996/G:46, 19 pp.

Sigurðsson, T. and Reynisson, P. 1998. Distribution of pelagic redfish in (S. mentella, Travin), at depth below 500 m, in the Irminger Sea and adjacent waters in May 1998. ICES CM 1998/O:75, 17 pp.

Sigurðsson, T., Rätz, H.-J., Pedchenko, A., Mamylov, V., Mortensen, J., Stransky, C., Melnikov, S., Drevetnyak, K., and Bakay, Y. 1999. Report on the joint Icelandic/German/Russian trawl-acoustic survey on pelagic redfish in the Irminger Sea and adjacent waters in June/July 1999. Annex to ICES CM 1999/ACFM:17, 38 pp.


Table 1. Extent, coverage and trawl specification of the international redfish survey in the Irminger Sea and adjacent waters in June/July 2013.

COUNTRY GERMANY ICELAND RUSSIA

Vessel RV Walther Herwig III RV Árni Friðriksson RV Vilnyus

Call code/ICES country code DBFR / 6 TNFA / 46 UFJN / 90

Days in field 14 22 24

Type of trawl Hampidjan / Gloria 1024 Hampidjan / Gloria 1024 Russian pelagic trawl (design 75/448)

Number of hauls 11 T1; 13 T2; 13 T3 = 37 7 T1; 41 T2; 40 T3 = 88 3 T1; 29 T2; 40 T3 = 72

Opening / Width 50 m / 50 m 50 m / 50 m 47-50 m

Codend Multisampler (3 bags), 23 mm codend

Multisampler (3 bags), 23 mm codend

40 mm codend

Distance for acoustic registrations

2,147 NM 2,800 NM 2,740 NM

Area surveyed 120,435 NM2 129,210 NM2 91,048 NM2

Number of CTD casts 36 50 45

Table 2. Instrument settings of the acoustic equipment on board the participating vessels. The sound speed value is approximate for the prevailing hydrographic condition in the survey area.

VESSEL WALTHER HERWIG III ÁRNIFRIÐRIKSSON VILNYUS

Echosounder Integrator

Simrad EK500 EchoView 4.9 (Myriax)

Simrad EK60 EchoView 5.0 (Myriax)

Simrad EK60 FAMAS

Frequency 38 kHz 38 kHz 38 kHz

Transmission power 2000 W 2000 W 2000 W

Absorption coefficient

9 dB/km 10 dB/km 10 dB/km

Pulse length 1.0 ms 1.0 ms 1.0 ms

Bandwidth Wide 2.43 kHz 2.43 kHz

Transducer type ES38-B ES38-B ES38-B

Two-way beam angle

-20.5 dB -20.9 dB -20.6

Integration Threshold

Time variable threshold

-80 dB/m3 -80 dB/m3

Sound speed 1495 m/s 1483 m/s 1478 m/s

Transducer Gain SV (sA correction)

26.78 dB -0.62 dB

-0.66 dB

Transducer Gain TS 26.83 dB 24.37 dB 25.92 dB


Table 3. Summary of biological sampling in the international redfish survey in the Irminger Sea and adjacent waters in June/July 2013.

COUNTRY GERMANY ICELAND RUSSIA TOTAL

Total number / biomass of redfish caught

872 ind. / 521 kg 1,974 ind. / 1,169 kg

553 ind. / 372 kg 3,399 ind. / 2,062 kg

Number of length measurements

872 1,974 553 3,399

Number of pairs of otoliths collected

872 1,811 474 3,157

Number of feeding analysis

872 1,811 553 3,236

Number of parasites analysis

872 1,811 553 3,236

Individuals with genetics

212 291 474 977

Table 4. Results of the acoustic abundance and biomass computation and area coverage for red-fish shallower than the DSL for each subarea and total in June/July 2013.

SUB-AREA A B C D E F TOTAL

Area (NM2) 123,531 83,385 4,181 51,185 62,730 15,683 340,695

No. fish ('000) 17,395 56,672 3,365 7,269 74,876 427 160,004

Biomass (t) 9,209 32,588 1,970 4,542 42,331 297 90,935

Table 5. Results (biomass in ´000 t) for the international surveys conducted since 1994, for redfish shallower than the DSL for each subarea and total.

SUB-AREA

YEAR A B C D E F TOTAL

1994 673 1228 - 63 226 2190

1996 639 749 - 33 155 1576

1999 72 317 16 42 167 614

2001 88 220 30 267 103 7 716

2003 32 46 1 2 10 0 89

2005 121 123 0 87 204 17 551

2007 80 95 0 53 142 3 372

2009 39 48 4 1 15 1 108

2011 5 74 0 3 40 1 123

2013 9 33 2 5 42 0 91


Table 6. Results from experimental estimation of redfish within the DSL and shallower than 500 m in June/July 2013.

A B C D E F TOTAL

Area (NM2) 123,531 83,385 4,181 51,185 62,730 15,683 340,695

Mean length (cm)

35.4 35.6 35.8 35.3 35.3 35.5

Mean weight (g) 529 547 575 534 534 542

No. fish ('000) 121,433 160,825 0 37,622 64,178 9,260 393,318

Biomass (t) 64,284 87,946 0 21,641 34,243 4,941 213,055

Lower CL 54,446 73,305 0 18,285 27,723 4,174 177,933

Upper CL 74,121 102,588 0 24,998 40,763 5,707 248,177

Table 7. Results (biomass in ´000 t) for the international surveys conducted since 2001, 2009, 2011 and 2013 for redfish within the DSL layer and shallower than 500 m for each subarea and the to-tal.

SUB-AREA

YEAR A B C D E F TOTAL

2001 23 40 45 399 54 5 565

2009 136 68 0 25 48 0 278

2011 69 185 1 30 76 0 309

2013 64 88 0 22 34 5 213

Table 8. Results from trawl estimation of redfish deeper than 500 m in June/July 2013.

A B C D E F TOTAL

Area (NM2) 123,531 83,385 4,181 51,185 62,730 15,683 340,695

Mean length (cm)

38.8 37.5 36.1 36.3 38.2 37.7

Mean weight (g) 717 653 615 595 482 654

No. fish ('000) 258,901 141,241 0 42,299 130,966 39,946 613,353

Biomass (t) 185,552 92,236 0 26,004 77,935 19,249 400,975

Lower CL 156,970 78,210 0 21,971 66,226 16,263 339,641

Upper CL 214,133 106,261 0 30,038 89,644 22,234 462,309


Table 9. Results (biomass in ´000 t) for the international surveys conducted since 1999, for redfish deeper than 500 m (1999–2003 and 2009–2013) and deeper than 350 m (2005 and 2007) for each sub-area and total, and the depth range covered.

SUB-AREA

YEAR A B C D E F TOTAL DEPTH (M)

1999 187 249 10 14 36 0 497 500–950

2001 497 316 28 79 64 18 1001 500–950

2003 476 142 20 13 27 0 678 500–950

2005 276 161 1 53 179 5 674 350–950

2007 345 283 2 32 172 19 854 350–950

2009 291 121 0 8 37 1 458 550-900

2011 342 112 0 1 18 0 474 550–900

2013 186 92 0 26 78 26 401 550-900

Table 10. Division of redfish biomass within NEAFC and NAFO areas in June/July 2013.

NEAFC NAFO

´000 T % ´000 T %

Acoustic <DSL 42 48 47 52

Trawl < 500 m (within the DSL)

152 71 61 29

Trawl > 500 m 278 69 123 31

Table 11a. Redfish trawl data < 500 m. Northeastern area. Mean weight and individuals by length (cm below).

LENGTH (CM)

MALES FEMALES TOTAL

WEIGHT (G) NUMBERS

WEIGHT (G) NUMBERS WEIGHT

(G) NUMBERS

28 269 2 257 1 265 3

29 266 5 275 2 268 7

30 302 3 307 10 306 13

31 337 8 351 9 345 17

32 383 25 382 10 383 35

33 424 21 423 22 424 43

34 467 49 453 21 462 70

35 508 40 496 48 501 88

36 556 67 546 37 552 104

37 599 34 586 26 594 60

38 658 23 635 39 643 62

39 701 11 694 17 696 28

40 765 7 791 6 777 13

41 827 2 768 5 785 7

42 801 3 801 3

43 965 4 965 4

Total number 301 256 557

Avg. weight 526 533 529

Avg. length 35.2 35.6 35.4


Table 11b. Redfish trawl data > 500 m. Northeastern area. Mean weight and individuals by length (cm below).

LENGTH (CM)

MALES FEMALES TOTAL

WEIGHT (G) NUMBERS WEIGHT (G) NUMBERS WEIGHT (G) NUMBERS

29 262 1 254 1 258 2

30 318 2 321 2 319 4

31 337 7 347 4 341 11

32 377 10 378 5 377 15

33 415 15 414 10 415 25

34 458 30 473 18 464 48

35 506 49 496 26 503 75

36 554 57 533 27 547 84

37 592 51 587 31 590 82

38 652 61 647 22 650 83

39 717 53 712 37 715 90

40 775 59 758 30 769 89

41 837 70 838 27 837 97

42 917 52 896 25 910 77

43 982 52 949 15 975 67

44 1019 37 994 10 1014 47

45 1069 16 1100 12 1083 28

46 1123 8 1171 3 1136 11

47 1134 1 1134 1


Avg. weight 728 694 717

Avg. length 38.97 38.50 38.82


Table 12a. Redfish trawl data < 500 m. Southeastern area. Mean weight and individuals by length (cm below).

LENGTH (CM)

MALES FEMALES TOTAL


26 227 1 227 1

27

28 259 1 259 1

29 273 3 313 2 289 5

30 318 8 310 4 315 12

31 357 9 359 6 358 15

32 393 11 410 6 399 17

33 435 33 432 14 434 47

34 489 53 478 23 486 76

35 538 87 520 47 532 134

36 586 89 570 66 579 155

37 623 58 608 51 616 109

38 675 27 662 40 667 67

39 709 7 707 29 707 36

40 802 2 754 14 760 16

41 935 1 812 3 843 4

42

43

44 950 1 950 1

45 1014 1 1014 1


Avg. weight 546 580 561

Avg. length 35.2 36.2 35.7


Table 12b. Redfish trawl data > 500 m. Southeastern area. Mean weight and individuals by length (cm below).

LENGTH (CM)

MALES FEMALES TOTAL


27 206 1 206 1

28

29 275 1 277 1 276 2

30

31 368 2,0 325 3 342 5,0

32 374 6 390 3 379 9

33 436 8 421 3 432, 11

34 462 12 472 5 465 17

35 515 9 503 8 509 17

36 549 15 559 7 552 22

37 658 10 587 12 619 22

38 661 11 665 11 663 22

39 722 9 713 8 717 17

40 790 7 898 1 803 8

41 824 14 850 6 832 20

42 890 7 911 4 898 11

43 1005 8 964 4 991 12

44 1069 3 1079 1 1072 4

45 1070 3 1070 3

46 1141 1 1141 1


Avg. weight 670 626 653

Avg. length 37.7 37.1 37.5


Table 13a. Redfish trawl data < 500 m. Southwestern area. Mean weight and individuals by length (cm below).

LENGTH (CM)

MALES FEMALES TOTAL


26 208 2 208 2

27 202 1 202 1

28 270 3 259 3 264 6

29 282 6 314 2 290 8

30 321 10 319 4 320 14

31 361 18 359 14 360 32

32 395 22 374 11 388 33

33 466 41 429 13 457 54

34 505 88 472 33 496 121

35 555 149 532 27 551 176

36 593 152 580 45 590 197

37 647 100 646 44 647 144

38 680 60 667 53 674 113

39 738 9 708 25 716 34

40 790 8 783 9 786 17

41 885 1 824 4 836 5

42

43 955 1 955 1


Avg. weight 564 575 567

Avg. length 35.3 35.9 35.5


Table 13b. Redfish trawl data > 500 m. Southwestern area. Mean weight and individuals by length (cm below).

LENGTH (CM)

MALES FEMALES TOTAL


30 350 1 350 1

31 328 1 300 1 314 2

32 405 3 430 1 411 4

33 405 1 405 1,0

34 496 4 489 1 494 5

35 513 6 513 6

36 583 3 583 3

37 612 6 646 4 625 10

38 647 4 647 4

39 758 4 798 1 766 5

40 743 2 743 2

41 880 2 880 2

42 877 1 877 1

43

44

45 1202 1 1202 1


Avg. weight 576 671 603

Avg. length 35.9 37.5 36.3


Table 14a. Length distribution (numbers of fish in ‘000 per cm class) of redfish by area, derived from the acoustic estimate <DSL.

LENGTH (CM) A B C D E F TOTAL

26 0 162 5 0 151 0 319

27 0 0 0 0 0 0 0

28 95 0 0 0 454 0 548

29 221 162 6 0 908 0 1,297

30 410 974 41 47 1,210 0 2,682

31 536 974 44 47 2,874 0 4,474

32 1,103 1,624 78 0 3,177 0 5,981

33 1,355 3,572 181 326 4,689 0 10,124

34 2,174 5,034 271 559 10,135 85 18,258

35 2,710 10,880 620 1,724 13,765 0 29,699

36 3,214 14,615 880 1,538 14,068 85 34,400

37 1,891 9,581 609 1,677 11,647 0 25,405

38 1,954 5,359 359 885 8,168 85 16,811

39 882 2,111 149 233 3,025 0 6,401

40 410 1,137 84 93 303 85 2,112

41 221 487 38 140 303 0 1,188

42 95 0 0 0 0 0 95

43 126 0 0 0 0 85 211

Total 17,395 56,672 3,365 7,269 74,876 427 160,004

Mean length 35.9 36.2 36.4 36.6 35.8 38.7 36.0

Mean weight (g) 529 575 586 625 565 695 568


Table 14b. Length distribution (numbers of fish in ‘000 per cm class) of redfish by area, derived from the trawl within the DSL and shallower than 500 m.


26 0 0 0 0 245 35 280

27 0 0 0 0 245 35 280

28 660 462 0 0 735 106 1,963

29 1,540 1,849 0 0 490 71 3,949

30 2,860 2,773 0 0 1,225 177 7,034

31 3,740 4,159 0 1,750 2,450 353 12,452

32 7,700 3,235 0 875 2,694 389 14,893

33 9,459 11,554 0 3,500 2,939 424 27,876

34 15,179 20,796 0 6,999 8,573 1,237 52,785

35 18,919 30,964 0 2,625 11,023 1,590 65,121

36 22,439 30,039 0 6,125 15,432 2,227 76,261

37 13,199 23,107 0 3,500 6,614 954 47,374

38 13,639 15,713 0 9,624 6,859 990 46,825

39 6,160 10,629 0 875 2,205 318 20,187

40 2,860 4,159 0 1,750 2,450 353 11,572

41 1,540 462 0 0 0 0 2,002

42 660 0 0 0 0 0 660

43 880 0 0 0 0 0 880

44 0 462 0 0 0 0 462

45 0 462 0 0 0 0 462

Total 121,433 160,825 0 37,622 64,178 9,260 393,318

Mean length 35.4 35.6 35.8 35.3 35.3 35.5

Mean weight (g) 529 547 575 534 534 542


Table 14c. Length distribution (numbers of fish in ‘000 per cm class) of redfish by area, derived from the trawl estimate ≥500 m.


27 0 692 0 0 0 0 692

28 0 0 0 0 0 0 0

29 553 1,385 0 0 0 0 1,938

30 1,106 0 0 207 3,358 0 4,672

31 3,043 3,462 0 622 6,716 0 13,843

32 4,149 6,231 0 207 13,432 0 24,020

33 6,915 7,616 0 2,281 3,358 0 20,170

34 13,277 11,770 0 4,147 10,074 7,989 47,258

35 20,745 11,770 0 8,709 13,432 0 54,656

36 23,235 15,232 0 8,501 6,716 7,989 61,673

37 22,681 15,232 0 8,294 33,581 0 79,788

38 22,958 15,232 0 6,220 13,432 7,989 65,832

39 24,894 11,770 0 1,451 10,074 0 48,190

40 24,618 5,539 0 829 6,716 7,989 45,691

41 26,831 13,847 0 829 3,358 0 44,865

42 21,298 7,616 0 0 3,358 0 32,273

43 18,532 8,308 0 0 0 7,989 34,830

44 13,000 2,769 0 0 0 0 15,770

45 7,745 2,077 0 0 3,358 0 13,180

46 3,043 692 0 0 0 0 3,735

47 277 0 0 0 0 0 277

Total 258,901 141,241 0 42,299 130,966 39,946 613,353

Mean length 38.8 37.5 36.1 36.3 38.2 37.7

Mean weight (g) 717 653 615 595 482 654


Table 15. Redfish trawl data. Observations on stomach contents, from fish caught shallower and deeper than 500 m.

< 500 M AREA

NORTHEAST SOUTHEAST SOUTHWEST TOTAL

No. % No. % No. % No. %

Everted 449 74.5 505 84,9 657 72,3 1611 78,2

Empty 82 11.1 46 7,7 135 14,9 263 12,8

Little 12 3.0 24 4,0 60 6,6 96 4,7

Medium 11 7.4 16 2,7 35 3,9 62 3,0

High 3 4.0 4 0,7 22 2,4 29 1,4

Total 557 595 909 2061

With content 26 4,7 44 7,4 117 12,9 187 9,1

> 500 M AREA

NORTHEAST SOUTHEAST SOUTHWEST TOTAL

No. % No. % No. % No. %

Everted 643 69,7 170 83,3 43 91,5 856 72,9

Empty 233 25,2 25 12,3 2 4,3 260 22,1

Little 28 3,0 5 2,5 0,0 33 2,8

Medium 17 1,8 2 1,0 1 2,1 20 1,7

High 2 0,2 2 1,0 1 2,1 5 0,4

Total 923 204 47 1174

With content 47 5,1 9 4,4 2 4,3 58 4,9


Table 16a. Redfish trawl data. Infestation with the copepod Sphyrion lumpi (according to remains of the parasite present) and skin pigment spots. Trawls shallower than 500 m.

Northeast Southeast Southwest Total

fem

ales

mal

es

tota

l

fem

ales

mal

es

tota

l

fem

ales

mal

es

tota

l

fem

ales

mal

es

tota

l

No. of fish examined 256 301 557 257 338 595 273 636 909 786 1275 2061 No. of fish with S. lumpi and/or rem-nants 129 130 259 145 153 298 167 231 398 441 514 955

% of fish with S. lumpi and/or remnants 50,4 43,2 46,5 56,4 45,3 50,1 61,2 36,3 43,8 56,1 40,3 46,3

No. of S. lumpi and/or remnants 250 241 491 390 313 703 563 449 1012 1203 1003 2206

Abundance index of S. lumpi invasion 1,0 0,8 0,9 1,5 0,9 1,2 2,1 0,7 1,1 1,5 0,8 1,1

No. of fish with external pigment spots 35 33 68 58 57 115 80 125 205 173 215 388

% of fish with external pigment spots 13,7 11,0 12,2 22,6 16,9 19,3 29,3 19,7 22,6 22,0 16,9 18,8

Table 16b. Redfish trawl data. Infestation with the copepod Sphyrion lumpi (according to remains of the parasite present) and skin pigment spots. Trawls deeper than 500 m.

Northeast Southeast Southwest Total

fem

ales

mal

es

tota

l

fem

ales

mal

es

tota

l

fem

ales

mal

es

tota

l

fem

ales

mal

es

tota

l

No. of fish examined 298 626 924 78 126 204 13 34 47 389 786 1175

No. of fish with S. lumpi and/or remnants 140 271 411 30 54 84 7 11 18 177 336 513

% of fish with S. lumpi and/or remnants 47,0 43,3 44,5 38,5 42,9 41,2 53,8 32,4 38,3 45,5 42,7 43,7

No. of S. lumpi and/or remnants 228 459 687 49 103 152 13 26 39 290 588 878

Abundance index of S. lumpi invasion 0,8 0,7 0,7 0,6 0,8 0,7 1,0 0,8 0,8 0,7 0,7 0,7

No. of fish with external pigment spots 22 34 56 15 9 24 4 4 8 41 47 88

% of fish with external pigment spots 7,4 5,4 6,1 19,2 7,1 11,8 30,8 11,8 17,0 10,5 6,0 7,5


Figure 1. Cruise tracks and stations taken in the joint international redfish survey in June/July

2013.

-60 -58 -56 -54 -52 -50 -48 -46 -44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 -18 -16

-60 -58 -56 -54 -52 -50 -48 -46 -44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 -18 -16

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68N

50

52

54

56

58

60

62

64

66

68

Greenland Iceland

A

B

CD

EF

Northeast

SoutheastSouthwest

Figure 2. Sub‐areas A‐F used on international surveys for redfish in the Irminger Sea and adjacent

waters, and divisions for biological data (Northeast, Southwest and Southeast; boundaries

marked by broken lines).


-54 -52 -50 -48 -46 -44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 -18 -16 -14

-54 -52 -50 -48 -46 -44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 -18 -16 -14

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

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N

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

Greenland IcelandA

B

CD

EF

SA-Values per 5 NM 0 0 - 1 1 - 5 5 - 12

Figure 3. Redfish acoustic estimates shallower than the DSL. Average sA values by 5 NM sailed

distance during the joint international redfish survey in June/July 2013.

Figure 4. Redfish acoustic estimates shallower than the DSL. Average sA values within statistical

rectangles during the joint international redfish survey in June/July 2013.


-54 -52 -50 -48 -46 -44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 -18 -16 -14

-54 -52 -50 -48 -46 -44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 -18 -16 -14

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

N

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

Greenland

IcelandA

B

CD

EF

NAFO NEAFC

SA-values 0

0 - 3

3 - 6

6 - 9

9 - 15

Figure 5. Redfish trawl estimates within the DSL and shallower than 500 m (type 2 trawls). sA

values calculated by the trawl method (Section 2.2.3) during the joint international redfish survey

in June/July 2013.


-54 -52 -50 -48 -46 -44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 -18 -16 -14

-54 -52 -50 -48 -46 -44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 -18 -16 -14

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IcelandA

B

CD

EF

NAFO NEAFC

SA-values 0

0 - 3 3 - 6 6 - 9

9 - 15

Figure 6. Redfish trawl estimates deeper than 500 m (type 3 trawls). sA values calculated by the trawl method (Section 2.2.3) during the joint international redfish survey in June/July 2013.


Figure 7. Regressions between catches and observed hydroacoustic sA values, observed on the German and Icelandic vessel(s) shallower than the DSL and used in the biomass calculations. For German trawl types 1 for the years 2001, 2005, 2009, 2011 and 2013 were used for the regression, the years 2005, 2007, 2009, 2011 and 2013 for the Icelandic vessel and 2007, 2011 and 2013 for the Russian vessel.


Figure 8. Screen print of a typical echogram of obtained on the German RV “Walther Herwig III” in bad weather.

0

50

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0 2 4 6 8 10 12 14 16 18 20 22

Time of the day (Hour; GMT)

Dep

th o

f the

DSL

Figure 9. Average depth and standard deviation of the DSL during the survey in June/July 2013.


0.00

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Figure 10. Diurnal variations of sA values of redfish in June/July 2013, along with 95% confidence limits. Data combined for all vessels.


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uals

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> 500 m

Figure 11. Length distribution of redfish in the trawls, by geographical areas (see Figure 2) and total, from fish caught shallower than 500 m (upper panel) and deeper than 500 m (lower panel).


0

25

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75

100

20 25 30 35 40 45 50

% m

atur

e

Length (cm)

Females <500 mMales <500 mFemales >500 mMales >500 m

Figure 12. Redfish trawl data 2013. Maturity ogives (ICES scale) by sex, shallower and deeper than 500 m.


53°

55°

57°

59°

61°

63°

65°

56° 52° 48° 44° 40° 36° 32° 28° 24°

0 m

Figure 13. Surface temperature (°C) distribution in the survey area of the international hydroa-coustic-trawl redfish survey on redfish in the Irminger Sea and adjacent waters in June/July 2013.

56° 52° 48° 44° 40° 36° 32° 28° 24°

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55°

57°

59°

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Figure 14. Temperature distribution (°C) at 200 m depth in the survey area of the international hydroacoustic-trawl redfish survey on redfish in the Irminger Sea and adjacent waters in June/July 2013.


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400 m


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Figure17. Temperature (°C) anomaly between 2011 and 2013 at 0 m, 200 m, 400m, and 600 m depth in the survey area of the international hydroacoustic-trawl redfish survey on redfish in the Irminger Sea and adjacent waters in June/July 2013.

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9(29)59°40' N26°15' W

08.07

Dep

th, m

Figure 18 Vertical temperature (°C) distribution on the 3K oceanographic section in the interna-tional hydroacoustic-trawl redfish survey on redfish in the Irminger Sea and adjacent waters in June/July 2013.


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1(21)62°15' N33°30' W

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5(25)61°00' N30°20' W

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8(28)60°10' N27°55' W

9(29)59°55' N27°05' W

9(29)59°40' N26°15' W

-5-4.5-4-3.5-3-2.5-2-1.5-1-0.500.511.522.533.544.55

Dep

th, m

Figure 19. Vertical temperature (°C) deviation on the 3K oceanographic section in the internation-al hydroacoustic-trawl redfish survey on redfish in the Irminger Sea and adjacent waters in June/July 2013.

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1(21)62°15' N33°30' W

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5(25)61°00' N30°20' W

6(26)60°40' N29°30' W

7(27)60°25' N28°40' W

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9(29)59°55' N27°05' W

9(29)59°40' N26°15' W

Dep

th, m

-5-4.5-4-3.5-3-2.5-2-1.5-1-0.500.511.522.533.544.55

Figure 20. . Temperature (°C) anomaly between 2011 and 2013 along the section 3К


Annex 1: List of participants

Name Address Telephone/Fax E-mail

Alexey Astakhov Knipovich Polar Research Institute of Marine Fisheries and Oceanography(PINRO) 6 Knipovitch Street 183038 Murmansk Russian Federation

TEL: +7 8152 47 25 32 FAX: +7 8152 47 33 31

[email protected]

Matthias Bernreuther

TI-Institute of Sea Fisheries, Palmaille 9 D-22767 Hamburg Germany

TEL: +49 40 38905–238 FAX: +49 40 38905–263

[email protected]

Eckhard Bethke TI-Institute of Sea Fisheries, Palmaille 9 D-22767 Hamburg Germany

TEL: +49 40 38905–203 FAX: +49 40 38905–264

[email protected]

Kristján Kristinsson (Chair)

Marine Research Institute Skúlagata 4 PO Box 1390 121Reykjavík Iceland

TEL: +354 575 2000 FAX: +354 575 2001

[email protected]

Alexey Rolskiy Knipovich Polar Research Institute of Marine Fisheries and Oceanography (PINRO) 6 Knipovich Street 183038 Murmansk Russian Federation

TEL: +7 8152 45 05 68 FAX: +7 8152 47 33 31

[email protected]


Annex 2: Agenda of the meeting

ICES Working Group on Redfish Surveys (WGRS) meeting

Hamburg, Germany, 6-8 August 2013

(Chair: Kristjan Kristinsson, Iceland)

Provisional Agenda

ToR (Recommendation 2011/2/SSGESST14):

b. at the 6-8 August meeting report on the outcome of the 2013 Irminger Sea survey.

Tuesday, 6 August 2013

09:00 Start of the meeting

• Housekeeping, network access • Suggestions for venues of lunch breaks and dinner • Adoption of the agenda

09:30 Plenary:

• Discussion of logistic and technical issues during the survey o Coverage deficiencies due to damages, bad weather, lack of time etc. o Deviations from survey planning (tracks, depth and duration of

trawling) o Hydroacoustics: transducer frequency and bandwidth, echo count-

ing(?), noise measurements o Biological sampling; unusual observations o Hydrography: short description of the situation during the survey

• Other relevant observations during the survey (e.g. intensity of fishery activi-ties, reports on catch rates of the fleet, targeted areas, depth zones etc.)

o Genetic sampling o Sampling of S. mentella on the Greenland slope o Echosounder comparison

• Preliminary biomass and abundance estimates, draft of main tables and fig-ures

12:00-13:00 Lunch break

13:00-17:00 Individual/subgroup work:

• Kristján: o cruise track plot o biomass and abundance estimation from acoustic method (shallower

than DSL) and from trawl-acoustic method (within and below DSL) o regression analyses

• Eckhard:


o echo counting results o report drafting for hydroacoustics section

• Russian oceanographer: o environmental conditions, temperature contour plots at

200/400/600m depth o report drafting for hydrography section

• Matthias: o plots of SA values by 5 NM and by trawl estimates o biological results o report drafting for biological and general sections o parasite infestation

Wednesday, 7August 2013

09:00 Plenary:

• Drafts of tables and figures for hydroacoustic estimation, trawl estimation, biology, environmental conditions

• Error estimation for abundance and biomass values • Description of uncertainties of the survey index

10:30 Continue individual/subgroup work (report drafting)


13:00 Plenary: General issues:

• Participation of further countries • Future of the survey, assessment relevance, financing, national inter-

ests/constraints • Other issues

15:00 Continue individual/subgroup work (report drafting)

17:00 Start discussion on first draft of report

18:00 End of working day.

Thursday, 8 August 2013

09:00-11:00 Finish first draft of report

11:00 Plenary:

• Perception of the state of the stock and corresponding advice • Recommendations • ToR and supporting information for 2015 planning and results meetings • ToR for the new working group, the Working Group on International Deep

Pelagic Surveys (WGIDEEPS) • The WGRS meeting in Reykjavik 20th September


13:00 Discuss draft report, clarify outstanding issues

Deadline for report: 1 September 2013

Leave all material (data, tables, figures, text parts etc.) on the server and with Kris-tján

16:00 End of the meeting


Annex 3: Regression models used in biomass calculations

Call: lm(formula = SaValue ~ kg.nm - 1, data = data[data$StType == 1 & data$Country == 90 & data$Year > 2005, ], na.action = na.omit) Residuals: Min 1Q Median 3Q Max -2.5981 -0.3366 0.3174 1.1124 3.4398 Coefficients: Estimate Std. Error t value Pr(>|t|) kg.nm 0.38316 0.02918 13.13 6.9e-12 *** --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 Residual standard error: 1.368 on 22 degrees of freedom (1 observation deleted due to missingness) Multiple R-squared: 0.8869, Adjusted R-squared: 0.8817 F-statistic: 172.5 on 1 and 22 DF, p-value: 6.901e-12

Model results for the German data Call: lm(formula = SaValue ~ kg.nm - 1, data = data[data$StType == 1 & data$Country == 6, ], na.action = na.omit) Residuals: Min 1Q Median 3Q Max -3.4655 -0.0050 0.4247 1.4022 4.7814 Coefficients: Estimate Std. Error t value Pr(>|t|) kg.nm 0.12594 0.01515 8.313 3.64e-10 *** --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 Residual standard error: 1.794 on 39 degrees of freedom (5 observations deleted due to missingness) Multiple R-squared: 0.6392, Adjusted R-squared: 0.63 F-statistic: 69.11 on 1 and 39 DF, p-value: 3.636e-10

Model reusults for the Icelandic data Call: lm(formula = SaValue ~ kg.nm - 1, data = data[data$StType == 1 & data$Country == 46 & data$Year != 2001, ], na.action = na.omit) Residuals: Min 1Q Median 3Q Max -6.3864 -1.1163 0.5587 2.6695 9.5377 Coefficients: Estimate Std. Error t value Pr(>|t|) kg.nm 0.18925 0.01498 12.64 4.5e-16 *** --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 Residual standard error: 3.274 on 43 degrees of freedom (2 observations deleted due to missingness) Multiple R-squared: 0.7879, Adjusted R-squared: 0.7829 F-statistic: 159.7 on 1 and 43 DF, p-value: 4.504e-16


Annex 4: WGIDEEPS Terms of Reference for the 2014 and 2015 meetings (draft, not finalized)

The Working Group on International Deep Pelagic Ecosystem Surveys [WGIDEEPS] (formerly the Working Group on Redfish Surveys [WGRS]; Co-Chairs: Kristjan Kristinsson, Iceland and [name to be decided]) will meet in ICES HQ, Copenhagen, Denmark, from 28-30 January 2014, in ICES HQ, Copenhagen, Denmark January 2015, [venue to be decided] (dates to be decided) August 2015 (to be confirmed), and in [venue to be decided] (dates to be decided) September 2015 (to be confirmed) to:

a ) transfer survey data from 2011 survey to ICES databases (January 2014 meeting);

b ) further develop the group strategy towards redfish assessment and ecosys-tem approach (January 2014 meeting);

c ) plan the international deep pelagic ecosystem survey with special empha-sis on redfish to be carried out in the Irminger Sea and adjacent waters in June/July 2015 (January 2015 meeting);

d ) plan the international deep pelagic ecosystem survey with special empha-sis on redfish to be carried out in the Norwegian Sea and adjacent waters in August 2015 (January 2015 meeting);

1. prepare the report on the outcome of the 2015 Irminger Sea survey (July 2015 meeting);

2. prepare the report on the outcome of the 2015 Norwegian Sea survey (Sep-tember 2015 meeting)

WGIDEEPS will report by 15 March 2014 (January 2014 meeting), 15 March 2015 (January 2015 meeting), 1 September 2015 (August 2015 meeting), and 15 September 2015 (September 2015 meeting) for the attention of the SCICOM and ACOM.

These terms of references depends on whether the group will renamed.


Supporting Information (not updated)

Priority: Essential, primary basis for the advice on the stock status of pelagic redfish in the Irminger Sea and adjacent waters.

Scientific Justification: This group was previously the Study Group on Redfish Stocks [SGRS] and the remit was slightly changed to the Planning Group on Redfish Surveys [PGRS] in 2009 and then Working Group on Redfish Surveys [WGRS] in 2010. WGRS is responsible for the plan-ning and reporting of the international hydroacoustic-trawl surveys on pelagic redfish (Sebastes mentella) in the Irminger Sea and Norwe-gian Sea. Redfish in the Norwegian Sea has been fished in an Olympic fishery by an international fleet since 2005. Since 2007, ICES has advised a protection of juveniles, no directed trawl fishery and low bycatch limits for S. mentella in Sub-areas I and II. NEAFC has, since 2007, set a TAC for pelagic S. mentella in this area. The unknown stock size and its relations to other S. mentella stocks have evoked the imme-diate need for an international survey on redfish in the Norwegian Sea and adjacent waters. WGRS has been responsible for the planning of the international trawl/acoustic surveys of redfish in the Irminger Sea and adjacent waters since 1994 and corresponding reports on the survey results. The observed drastic changes in abundance and biomass estimates since 1994 and considerable changes in environmental conditions in recent years confirm the need of precise monitoring of the redfish in the distribution area. WGRS, however, repeatedly faced the problem of a large spacing between hydroacoustic survey tracks and between trawl hauls due to the large survey area (about 400,000 square nautical miles) that has to be covered with only two or three vessels currently participating in the survey. In order to reach a sufficient density of survey tracks and trawls, PGRS recommended (ICES CM 2007/D:03) that “as many vessels as possible (at least four) should participate to improve the quality of the derived estimates. Thus, the efforts directed at involving other nations in the survey should be continued.” Consequently, the potential countries were requested to consider a participation in the redfish survey in June/July 2007. This request was repeated in 2008 and 2011 without success. In 2007 and 2009, only 2 vessels participated in the survey which is insufficient in terms of data quality for the assessment.

Relation to Strategic Plan: Provide sound, credible, timely, peer-reviewed, and integrated scientific advice on fishery management and the protection of the marine environment in response to requests from regulatory commissions, Member Countries, and partner organizations.

Resource Requirements : N/A

Participants : <10 (incl. the cruise leaders of each vessel and the principle experts involved in abundance and biomass calculations)

Secretariat Facilities: N/A

Financial: None

Linkages to Advisory Committees:

ACOM, SSGESST

Linkages to other Committees or Groups:

NWWG, AFWG

Linkages to other Organizations:

NAFO, NEAFC


Annex 5: Recommendations

RECOMMENDATION ACTION

The Working Group on Redfish Surveys (WGRS) will be renamed: Working Group on International Deep Pelagic Surveys (WGIDEEPS)

ICES SSGESST/Scicom

The working group will meet in ICES HQ, 28-30 January 2014 to 1) Transfer survey data from 2009 to ICES databases and 2) further develop the group strategy towards redfish assessment and ecosystem approach

WGIDEEPS members/Scicom

Continue international trawl-acoustic survey on pelagic redfish in the Irminger Sea and adjacent waters; keep survey frequency (every second year); participation of as many vessels as possible; keep timing of the survey (June/July)

ICES Secretariat, ICES Delegates, ICES Member Countries

Consider 2013 survey results for advice on pelagic redfish (shallow and deep stocks) to be given in October 2013

ACOM, NWWG

Involve further nations in the next surveys; Consider chartering of additional vessels and cost share

ICES Secretariat, ICES Delegates

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