A Pilot Study of Commercial Fishing Gear Selectivity during the 2012/13 Aleutian Islands ...

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A Pilot Study of Commercial Fishing Gear Selectivity during

the 2012/13 Aleutian Islands Golden King Crab Fishery

Vicki Vanek, Doug Pengilly, Shareef SiddeekADF&G, Kodiak & Juneau

Presented at May 2013 NPFMC-CPT Crab Plan Team meeting

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8 May 2012 evening meeting in ANC: CPT members, ADF&G staff, NMFS-AFSC staff, and Industry members and representatives. •Identify data needs for AIGKC stock assessment•Means for collecting such data given prohibitively expensive survey vessel charter costs

• Last two surveys (2009 and 2012) cancelled.

•Four broad priority research objectives emerged:1. Obtain an “abundance scaler” for the AIGKC fishery-based stock assessment

model2. Obtain fishery-independent data on stock distribution and size frequency

distribution3. Obtain an explanatory variable(s) for the increased fishery CPUE that followed

fishery rationalization4. Obtain data to better estimate basic parameters for the AIGKC fishery-based

stock assessment model: growth and molting probability throughout the stock distribution, fishery and fishing gear selectivity, and natural mortality.

•Three broad classes of approaches advanced/discussed:1. Tagging studies2. Fishery-independent data collection on stock and size frequency distribution3. Use of modified pots during the fishery

Motivation

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Research priorities from NPFMC Crab Plan Team, May 2012 meeting:• Explore alternative approaches to the triennial ADF&G Aleutian Islands golden king

crab pot survey to acquire fishery-independent abundance data on stock distribution and recruitment, including the potential for future cooperative research efforts with Industry.

• Explore use of tagging studies on Aleutian Islands golden king crab to better measure absolute abundance that could be used to scale the stock assessment model.

• Particular emphasis should be placed on … fishery and fishing gear selectivity for Aleutian Island GKC to improve the stock assessment model.

Motivation

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1. Explore ways to improve size frequency distribution data on the Aleutian Islands golden king crab (AIGKC) stock and means to provide data to estimate fishing gear selectivity

2. Explore use of modified pots by cooperating commercial fishing vessels to gather data from the stock

Objectives

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0

5

10

15

20

25

30

35

40

45

CPU

E

Fishery Year

Male CPUE East of 174° W Longitude

Legal Males

≥ 121 mm CL

< 121 mm CL

Two trends in fishery data since mid-2000’sa) Increased CPUE of legal malesb) Shift in male size frequency distribution towards larger males

Observer data from area east of 174° W longitude

BACKGROUND

Legal Males

Sublegal Males => 121mm CL

< 121 mm CL

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BACKGROUND

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BACKGROUND

•1995/96: 33% > 135 mm CL

•2011/12: 81% > 135 mm CL

LEGAL

136-150 mm CL

> 150 mm CL

SUBLEGAL

121-135 mm CL

101-120 mm CL

< 101 mm CL

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Possible explanations

1. Shift reflects reality/population Stock aging, recruitment failure?• Not likely, given the trend in legal-sized male CPUE• See also: Siddeek et al. (various reports to Crab Plan Team)

2. Changes in fishery practices, especially since rationalization (2005/06)

a) Fishery can better target areas with high densities of large males, lower densities of sublegal males?• Less boats/competition, more time “smarter fishing”

b) Longer soak time & more escape mesh sublegals escape?

Why the “Shift in male size frequency distribution towards larger males”?

East of 174°Pre-rat’ized avg soak time = 4.4 daysPost-rat’ized avg soak time = 15.2 days

West of 174°Pre-rat’ized avg soak time = 10.4 daysPost-rat’ized avg soak time = 23.9 days

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AIGKC Industry - Aleutian Golden King Crab Research Foundationsupplied 20 specially-made, small-mesh pots

Pilot study: Use of “small mesh research pots” on commercial vessel during commercial fishing

Small Mesh Research Pots

Size : 7' x 7'Webbing: 2.5" stretchNo escape mesh or ringsBased on ADF&G survey pot

specifications

Commercial Fishing PotsObserved in this study:

Size: 5' x 5' to 6.5' x 7'Escape mechanism (generally):

9" stretch mesh on pot door & 9" stretch mesh on tunnel sides, top

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PILOT STUDY PLAN

Deploy “research pots” with commercially-fished gear during fishery• One “research pot” per long-lined string• Randomly-determined location within string (except anchor pot position at ends)

• 30 to 50 pots per long-lined string• 80 fathoms of line between pots

• “Research pot” fished with commercial gear during normal fishing• Not “prospecting” for small crab

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•Sex•Size - mm CL•Shell Condition•Legality as measured with 6.0“ stick•Female reproduction

• Paired pots in string at hauling:1) “Research pot” in string2) The next commercial pot in the

string hauled after the research pot• Note: pots in a string are not

always hauled in same order they were set

• Catch sampling of paired pots:

Sampling of “Paired Pots”at Hauling of a String

• Sampling emphasized catch of male golden king crab

• All male GKC measured

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Data collected on sampled pots:• Set/haul date-time (soak time)• Haul location • Haul depth• Specs (dimensions, escape mechanism) of commercial pots• Temperature recordings from loggers placed in 8 research pots

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• Two trips on the F/V Aleutian No. 1• Oct 29 – Nov 6, 2012• Nov 10 – 21, 2012

• Two ADF&G biologists working alongside commercial crew

• EAST of 174° W longitude – centered in Amukta I to Yunaska I area

• 31 pairs of “research” and commercial pots sampled• Soak times: 11 to 31 days (Ave = 20 days)• Depth: 120 to 350 fathoms (Ave = 194 fathoms)

Work and results

Fishing spanned area: ~80 nm, E to W~40 nm, N to S

52° 30' N

171° 00' W172° 00' W52° 00' N

Chuginadak I

Islands of Four Mountains

53° 00' N

Amukta I

170° 00' W

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Work and results

Positions of paired Research pots and Commercial pots in sampled long-lined strings

13579

1113151719212325272931333537394143454749515355575961

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 28 29 30 31 32 33

Posi

tion

in st

ring (

1 de

note

s firs

t pot

set i

n st

ring)

Pot pair

C pot R pot Last pot set in string

• C pot closer to a string end than R pot in 15 strings (48%)• C pot set before the R pot in 9 strings (29%)

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Work and results

Haul depths of paired Research pots and Commercial pots in sampled long-lined strings

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50

100

150

200

250

300

350

400

100 125 150 175 200 225 250 275 300 325 350 375 400

Com

mer

cial

pot

hau

l dep

th (f

atho

ms)

Research pot haul depth (fathoms)

•R pot avg depth = 193.7 fathoms•C pot avg depth = 193.5 fathoms

• C pot deeper in 6 string• C pot less deep in 5 strings

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Results on male golden king crab from 31 pairs of “research” and commercial pots

52° 30' N

171° 00' W172° 00' W52° 00' N

Chuginadak I

Islands of Four Mountains

53° 00' N

Amukta I

170° 00' W

Male golden king crab catch30015030

C pot catchR pot catch

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Results on golden king crab from 31 pairs of “research” and commercial pots

a. Number of pots

Pot TypeMale, sublegal

<101 mm CLMale, sublegal 101-120 mm CL

Male, sublegal >120 mm CL Male, legal Female

Commercial 2 13 27 31 24Research 20 26 31 31 29

b. Percent of pots

Pot TypeMale, sublegal

<101 mm CLMale, sublegal 101-120 mm CL

Male, sublegal >120 mm CL Male, legal Female

Commercial 6% 42% 87% 100% 77%Research 65% 84% 100% 100% 94%

Sex-size class Commercial "Research" TotalMale, sublegal <101 mm CL 4 479 483Male, sublegal 101-120 mm CL 25 796 821Male, sublegal >120 mm CL 276 962 1,238Male, legal 1,172 1,378 2,550Total males 1,477 3,615 5,092Females, all sizes 286 2,524 2,810Total males and females 1,763 6,139 7,902

Pot Type

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

Males, Sub<101 mm CL Males, Sub 101-120 mm CL Males, Sub>120 mm CL Males, Legal Females

Catc

h pe

r pot

lift

Sex-size class

C pots R pots

Differences statistically significant for all sex-size classes except legal males

Statistically significant difference in presence/absence for all sex-size classes except sublegal >120 mm CL

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Males, Sub<101 mm CL Males, Sub 101-120 mm CL Males, Sub>120 mm CL Males, Legal Females

Perc

ent w

ith ca

ptur

ed cr

ab

Sex-size class

C pots R pots Pot pairs

a. NUMBER OF POTS WITH CATCH >0

b. PERCENT OF POTS WITH CATCH >0

CATCH OF GOLDEN KING CRAB

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Results on golden king crab from 31 pairs of “research” and commercial pots

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100

200

300

400

500

600

53 58 63 68 73 78 83 88 93 98 103 108 113 118 123 128 133 138 143 148 153 158 163 168 173 178 183 188 193

Freq

uenc

y

Carapace length (mm) - mid-point of 5-mm size class

C pots R pots Total

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50

100

150

200

250

300

350

400

53 58 63 68 73 78 83 88 93 98 103 108 113 118 123 128 133 138 143 148 153 158 163 168 173 178 183 188 193

Freq

uenc

y

Carapace length (mm) - mid-point of 5-mm size class

C pots R pots Total

Male size frequency

Female size frequency

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Comparison of male size frequency in research and sampled commercial pots with male size frequency from observer pot sample data, 1995/96 – 2011/12, east of 174° W long.

•C pot: legal CPUE = 38; sublegal CPUE = 10•R pot: legal CPUE = 44; sublegal CPUE = 72•2011/12 fishery E of 174° W: legal CPUE = 40; sublegal = 13 (observer data)

→ Sampled C pots were representative of current commercial fishing

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

12.0%

14.0%

16.0%

18.0%

60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Rela

tive

freq

uenc

y

Carapace length (upper limit of 5-mm group)

1995/96

1996/97

1997/98

1998/99

1999/00

2000/01

2001/02

2002/03

2003/04

2004/05

2005/06

2006/07

2007/08

2008/09

2009/10

2010/11

2011/12

C pots

R pots

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Cum

ulati

ve re

lativ

e fr

eque

ncy

Carapace length (upper limit of 5-mm group)

1995/96

1996/97

1997/98

1998/99

1999/00

2000/01

2001/02

2002/03

2003/04

2004/05

2005/06

2006/07

2007/08

2008/09

2009/10

2010/11

2011/12

C pots

R pots

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Comparison of male size frequency in research pots with male size frequency from most recent (2006) pot survey east of 174° W long.

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Estimation of commercial-fishing pot selectivity curve (for males only)•“SELECT” method (Millar and Fryer 1999) •Research pots considered “control” – assumed to retain all that enter

• Estimating “contact-selectivity” curve (Millar and Fryer 1999)• Probability of retention at size, given entered pot

•Symmetric logistic function for selectivity:• S(l) = [e(a+bl)]/[1+e(a+bl)]

•Assumed equal relative fishing intensities for Research pots and Commercial potsSize class mid-point C pots R pots Total

C pot pecentage

58 0 3 3 0.0% 63 0 2 2 0.0% 68 0 38 38 0.0% 73 1 55 56 1.8% 78 0 68 68 0.0% 83 2 59 61 3.3% 88 1 54 55 1.8% 93 0 95 95 0.0% 98 0 105 105 0.0%

103 1 146 147 0.7% 108 0 165 165 0.0% 113 6 197 203 3.0% 118 18 288 306 5.9% 123 31 305 336 9.2% 128 69 339 408 16.9% 133 153 326 479 31.9% 138 206 322 528 39.0% 143 237 220 457 51.9% 148 235 231 466 50.4% 153 148 180 328 45.1% 158 111 138 249 44.6% 163 117 99 216 54.2% 168 72 77 149 48.3% 173 40 55 95 42.1% 178 17 30 47 36.2% 183 10 12 22 45.5% 188 2 6 8 25.0%

Total 1,477 3,615 5,092 -

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100

200

300

400

500

600

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Tota

l num

ber c

aptu

red

Perc

ent c

aptu

red

by co

mm

erci

al fi

shin

g pot

s

Carapace length (mid-point of 5-mm group)

Percent captured by commercial pots Total number captured by research and commercial pots

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Estimation of commercial-fishing pot selectivity curve (for males only)•“Assumed equal relative fishing intensities for Research pots and Commercial pots”

• Effects of pot sizes? “Research pots” were 7x7, commercial pots smaller.

5 x 55 x 5.5

5.5 x 6 6 x 66 x 6.5

6 x 76.5 x 7

POTSIZE

0

1

2

3

4

5

6

7

8

9

Cou

nt

0.0

0.1

0.2

Proportion per B

ar

5 x 55 x 5.5

5.5 x 6 6 x 66 x 6.5

6 x 76.5 x 7

POTSIZE

0

20

40

60

80

100

120

TOTA

L

5 x 55 x 5

.55.5 x 6 6 x 6

6 x 6.56 x 7

6.5 x 7

POTSIZE

10

20

30

40

50

60

70

80

90

100

MA

LE

5 x 55 x 5.5

5.5 x 6 6 x 66 x 6.5

6 x 76.5 x 7

POTSIZE

10

20

30

40

50

60

70

80

90

100

LEG

AL

Size distribution of sampledCommercial pots

Catch of GKC by commercial pot sizes:

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Estimation of commercial-fishing pot selectivity curve (for males only)

Parameter Estimate a -23.735 (1.472) b 0.1765 (0.0115) l25 (mm CL) 128.27 (0.49) l50 (mm CL) 134.50 (0.64) l75 (mm CL) 140.72 (0.95) SR (mm CL) 12.45 (0.81) Model deviance 36.64 [77.30] df 14 [25]

Estimated parameters (with standard error estimates).

•Significant overdispersion:P = 0.0008 for χ2 = 36.64, df = 14

→ Standard error estimates unreliable •Need to estimate by resampling pot pairs w/r

• Keeping with “paired-pot” study design

Results:

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Comparison of selectivity estimates for post-rationalized fishery east of 174° W• This study• Siddeek et al., Jan 2012• Siddeek et al., Feb 2013

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

93 98 103 108 113 118 123 128 133 138 143 148 153 158 163 168 173 178 183 188

Sele

ctivi

ty

Carapace length (mm)

This study 2013 model (Scenario 1) 2012 model (Scenario 2)

This study: S(l) = exp(-23.735+0.1765·l)/[1+ exp(-23.735+0.1765·l)]2013 model (Scenario 1): S(l) = {1+exp[-ln(19)(l-133.89)/18.43]}-1

2012 model (Scenario 2): S(l) = {1+exp[-0.1122(l-135.03)]}-1

L50% estimates• This study: 134.5 mm CL• 2013 model: 133.9 mm CL• 2012 model: 135.0 mm CL

•i.e., ~135 mm CL≈ legal size

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Conclusions

• There ARE more sublegal males on the fishing grounds than in current fishery data!• Fishery effort has NOT entirely shifted to “low-bycatch” areas• At currently-used soak times, currently-used gear (escape mesh, etc) DOES

reduce bycatch of sublegal males (and females)• Can gain more information on stock in areas fished using “research pots” during

fishery• Sublegal males and females

• Contact-selectivity for males estimated here essentially the same as fishery selectivity estimated by 2013 model (Scenario 1) • Male l50% ≈ 135 mm CL

• cf. 136 mm CL legal size proxy

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Pilot study – Seeking input from CPT on direction:Future use of “research pots” during commercial fishery?

• Data (or more similar data) useful for stock assessment model?• Estimation of selectivity or validation of model selectivity estimates?

• Direction or recommendations on use of “research pots” on commercial vessels for stock assessment needs?• Data collected during commercial fishing ? versus • Data collected independent of fishery (survey)?

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Thanks to:• Captains and crew of the F/V Aleutian No. 1:

• Rip Carlton – captain• Rick Alverez – captain• Sean Doran “Flany” – engineer• Roberto Rizo• Willy Olvalles• James Grigg “Shaggy”• Luke Smith• Ray Moe

• Aleutian Golden King Crab Research Foundation• Denby Lloyd

• ADF&G research crew: Dmitri DelaCruz – biologist

• Susan Strand, observer onboard F/V Aleutian No. 1

• Norton Sound Economic Development Corp (owner of boat)

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A Pilot Study of Commercial Fishing Gear Selectivity during the 2012/13 Aleutian Islands ...

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