SARC-59 Sea Scallop Assessment. Dvora Hart, NEFSC

Transcription

1 SARC-59 Sea Scallop Assessment Dvora Hart, NEFSC

2 Historical landings - All U.S. and Canada-Georges Bank (NAFO areas 5 and 6) CANADA USA Landings (MT, meats) Year Hague Line Limited access

3 U.S. landings by region

4 Landings by meat count category (by weight) Meat count categories: U10: <10 mpp (> 45g) 1020: mpp (23-45 g) 2030: mpp (15-23 g) 3040: mpp (11-15 g) 40+: >40 mpp (<11 g) Draft document Do not distribute, circulate or cite

5 Dredge Surveys For the first time, VIMS survey data (survey dredge only) was integrated into the dredge survey index for VIMS data had modest effects on index, but improved CVs Tows were standardized to 1nm tow path (instead of using a vessel correction factor) Marginal areas on Georges Bank were dropped from the survey index

6 Combined NEFSC/VIMS Dredge Survey for 2013

7 Dredge Survey Time Series

8 C3D sidescan sonar Water spectrometer Cameras (x2) CTD, DO, CDOM, ph etc sensors Altimeter and attitude sensors Main bottle/ networking hub Strobes (x4) Used as a survey index for the first time (Georges Bank , Mid-Atlantic ) Habcam surveys GAM + Ordinary Kriging model used to obtain biomass and abundance estimates. Stratified mean used as backup and sanity check Paired Habcam/Dredge tows used to obtain survey dredge efficiency estimates Habcam 8 survey dredge

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10 Comparison of Survey Time Series Georges Bank Mid-Atlantic Combined

11 CASA models Three models used for this assessment GB open, GB closed, Mid-Atlantic. Previous assessments used only two. Natural mortality increased in all areas. Plus group M was assumed to be 1.5 times that of other sizes. Growth varied by period heavy fishing corresponded to slow growth

12 Comparison of recent growth to that from Growth from two periods appears similar at small shell heights, but fast growing scallops appear to be preferentially removed at commercial sizes

13 Georges Bank Open model. Model estimates reasonably agree with surveys; model has almost no retrospective pattern

14 Georges Bank Closed CASA biomass below surveys during , but above during most recent period. Moderate retrospective pattern GBK-closed Abundance (survey vs. model) GBK-closed Biomass (survey vs model) 8e+04 6e+09 Abundance 4e+09 CASA Dredge SMAST HabCam Biomass (1000mt) 6e+04 CASA Dredge SMAST HabCam 4e+04 2e+09 2e Year Year

15 Mid-Atlantic Model estimates tend to be below surveys, especially after strong recruitment. Retrospective pattern Models may be suggesting density-dependent mortality among juveniles Mid-Atlantic Abundance (survey vs. model) Mid-Atlantic Biomass (survey vs model) e+10 Abundance 1.0e+10 CASA Dredge SMAST HabCam Biomass (1000mt) CASA Dredge SMAST HabCam e Year Year

16 Whole stock (GB + MA) biomass and fishing mortality estimates estimates: F = 0.32, B = thousand mt

17 Reference points computed using the Stochastic Yield Model, that takes into account uncertainty in model parameters such as natural mortality and stock-recruit relationships Mean total yield (mt) Mid-Atlantic Mean total yield (mt) Georges Bank Fishing mortality Fishing mortality

18 The model outputs distributions of reference points such as MSY and F MSY Distribution of whole-stock MSY Density Distribution of whole-stock F MSY Fmsy

19 Whole stock yield boxplot

20 New Reference Points FMSY = 0.48, MSY = 23,798 mt, BMSY = 96,480 mt Increase in F MSY due to increases in M and weakening of Mid-Atlantic stock-recruit relationships

21 Overfished (biomass) status determination: Estimated biomass in 2013 from CASA: Estimated B MSY from SYM: Biomass (overfished) threshold: ½ B MSY = 132,561 mt 96,480 mt 48,240 mt Fishing mortality (overfishing) status determination: Estimated fishing mortality in 2013 from CASA: 0.32 Estimated F MSY from SYM: 0.48 Biomass is above B MSY and F was below F MSY so sea scallops were not overfished and overfishing did not occur in 2013

22 Modest chance that overfishing is occurring and almost no chance that the stock is overfished The CASA model errors are likely underestimated, and CASA has a tendency to overestimate biomass and underestimate F, so that these figures underestimate the true errors of the CASA estimates

23 Example projections, based on 2013 data