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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 Siddeek.

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Presentation on theme: "A Pilot Study of Commercial Fishing Gear Selectivity during the 2012/13 Aleutian Islands Golden King Crab Fishery Vicki Vanek, Doug Pengilly, Shareef Siddeek."— Presentation transcript:

1 A Pilot Study of Commercial Fishing Gear Selectivity during the 2012/13 Aleutian Islands Golden King Crab Fishery Vicki Vanek, Doug Pengilly, Shareef Siddeek ADF&G, Kodiak & Juneau Presented at May 2013 NPFMC-CPT Crab Plan Team meeting 1

2 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 model 2.Obtain fishery-independent data on stock distribution and size frequency distribution 3.Obtain an explanatory variable(s) for the increased fishery CPUE that followed fishery rationalization 4.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 studies 2.Fishery-independent data collection on stock and size frequency distribution 3.Use of modified pots during the fishery Motivation 2

3 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 3

4 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 4

5 Two trends in fishery data since mid-2000’s a)Increased CPUE of legal males b)Shift in male size frequency distribution towards larger males 5 Observer data from area east of 174 ° W longitude BACKGROUND Legal Males Sublegal Males => 121mm CL < 121 mm CL

6 Two trends in fishery data since mid-2000’s a)Increased CPUE of legal males b)Shift in male size frequency distribution towards larger males 6 Observer data from area east of 174 ° W longitude BACKGROUND

7 Two trends in fishery data since mid-2000’s a)Increased CPUE of legal males b)Shift in male size frequency distribution towards larger males 7 Observer data from area east of 174 ° W longitude BACKGROUND 1995/96: 33% > 135 mm CL 2011/12: 81% > 135 mm CL LEGAL mm CL > 150 mm CL SUBLEGAL mm CL mm CL < 101 mm CL

8 8 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 days Post-rat’ized avg soak time = 15.2 days West of 174 ° Pre-rat’ized avg soak time = 10.4 days Post-rat’ized avg soak time = 23.9 days

9 9 AIGKC Industry - Aleutian Golden King Crab Research Foundation supplied 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" stretch No escape mesh or rings Based on ADF&G survey pot specifications Commercial Fishing Pots Observed 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

10 10 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

11 11 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 string 2)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

12 12 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

13 13 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

14 14 Work and results Positions of paired Research pots and Commercial pots in sampled long-lined strings 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%)

15 15 Work and results Haul depths of paired Research pots and Commercial pots in sampled long-lined strings R pot avg depth = fathoms C pot avg depth = fathoms C pot deeper in 6 string C pot less deep in 5 strings

16 16 Results on male golden king crab from 31 pairs of “research” and commercial pots

17 17 Results on golden king crab from 31 pairs of “research” and commercial 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 a. NUMBER OF POTS WITH CATCH >0 b. PERCENT OF POTS WITH CATCH >0 CATCH OF GOLDEN KING CRAB

18 18 Results on golden king crab from 31 pairs of “research” and commercial pots Male size frequency Female size frequency

19 19 Results on male golden king crab from 31 pairs of “research” and commercial pots 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 = /12 fishery E of 174° W: legal CPUE = 40; sublegal = 13 (observer data) → Sampled C pots were representative of current commercial fishing

20 20 Results on male golden king crab from 31 pairs of “research” and commercial pots Comparison of male size frequency in research pots with male size frequency from most recent (2006) pot survey east of 174 ° W long.

21 21 Results on male golden king crab from 31 pairs of “research” and commercial pots 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 pots

22 22 Results on male golden king crab from 31 pairs of “research” and commercial pots 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. Size distribution of sampled Commercial pots Catch of GKC by commercial pot sizes:

23 23 Results on male golden king crab from 31 pairs of “research” and commercial pots Estimation of commercial-fishing pot selectivity curve (for males only) Estimated parameters (with standard error estimates). Significant overdispersion: P = for χ 2 = 36.64, df = 14 → Standard error estimates unreliable Need to estimate by resampling pot pairs w/r Keeping with “paired-pot” study design Results:

24 24 Results on male golden king crab from 31 pairs of “research” and commercial pots Comparison of selectivity estimates for post-rationalized fishery east of 174 ° W This study Siddeek et al., Jan 2012 Siddeek et al., Feb 2013 L 50% estimates This study:134.5 mm CL 2013 model: mm CL 2012 model:135.0 mm CL i.e., ~135 mm CL≈ legal size

25 25 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 l 50% ≈ 135 mm CL cf. 136 mm CL legal size proxy

26 26 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)?

27 Thanks to: 27 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 )

28 28 THE END


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