Review of Northeast Fishery Stock Assessments (1998) / Chapter Skim
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D. Presentation to the Committee by NMFS Scientists
D. Presentation to the Committee by NMFS Scientists
Pages 104-115
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From page 104... ...
Murawski Databases, Survey Calibration, Assessment, and Prediction Methods Assessments Inputs, Assumptions, Results, and Research Recommendations S Murawski 10:45-11:00 Georges Bank Haddock R
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From page 105... ...
I vO_(S4 · ~icF~Ub~ 105 Information Presented SAW-24 AGENDA Stocks - Gulf of Maine Cod - Georges Bank Cod - Georges Bank Haddock Georges Bank Yellowtail Flounder Southern New England Yellowtail Flounder . Terms of Reference Assess the stock status through 1996 and characterize the variability of estimates of stock abundance and fishing mortality rates Provide projected estimates of catch for 1997-1998 and SSB for 1998-1999 at various level of F
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From page 106... ...
f .' . ~ f 7 t ~fi <2 ;~.,r~ Generic Assessment Issues I Assessment Databases - Changes in Landings Data Collection System - Proration of Landings to Stock Area - Effort&CPUE/LPUE - Rates of Biological Sampling of the Catch - Discard Estimates Survey Calibration Studies Vessel/Door/Net Changes over Time Estimation of Calibration Coeffcients Effects of Altemative Estimation Methods Genenc Assessrr7ent Issues 11 Uncert~irr~ in Assessm~ Bootstrap Estimates of Precision in ADAPT Sensitivity of Assessment Results to Potential Biases Explicit vs.
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From page 107... ...
Investigate factors associated with apparent recent improvements in survivalratios (R/SSB)
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From page 108... ...
Review of Northeast Fishery Stock Assessments Georges Bank Cod Assessment Summary Current landings (1996) = 8,900; up from 7,900 mt in 1995 Survey indices fluctuate near record-low values LPUE declined by 1993 to the lowest LPUE in time series VPA results CurrentF(1996)
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From page 109... ...
F ~ ff x ~ i n ~ i = # ff ~ e b a s i s f o r d e r i v i r ~ ff ~ e To - ~olfffecod~ch Spicily, He ~ecta~s~ir~levelsin Be -did-ate abed art me oarrr~rcral landers at age in He US f ~ ecarane USA tales in yew prior to 1~9 beam cyst ~ can be I inJoff~at~ 109 Gulf of Maine Cod Assessment issues / Dafa Used CURRENT ASSESSMENT - ANALYTICAL (Age Structured) - ADAPT VPA Calibration of Age 2-7 ~ CAN, 1982-1996 - ANALYTICAL (Age Structured - ADAPT VPA Calibration of Age 2-7+ CAA, 1982-1996 1996 landings were 7,200 t; up from 6,800 t in 1995 Sample summary 1994-1995 sampling improved over 1993, but tow re landings 1996 much improved Catch at Age - Reduction in proportion of older 9~7 yrJ ages and few fish >9 yr after 1990 1992 year class 62% by number, 57% by weight in 1996 Commercial LPUE - LPUE declined in 1993 to pre-1989 level; not used in 1994-1996 Survey Indices Low number and weight per tow persist through autumn 1996 Low recruitment indices in NEFSC and Massachusetts DMF surveys in 1995 and 1996 Survey Zx 1 1 in 1991-1993 and 1994-1996 VPA Calibration Unusual F pattern in 1994 for fully recruited ages 4 and 5 Record low recruitment of 1994 and 1995 year classes <1 million fish
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From page 110... ...
samples pooled on annual basis Gulf of Maine Cod Assessm ent issues-/// Alternative Runs Six alternative assessment models using Stock Synthesis A pproach (Fournier and Archibald, 1982J Employed same survey indices as ADAPT Conclusions - Included commercial CAA alone and commercia/ and recreational CAA - Lognormal, multinomial, and robust error structure assumptions Lognormal mode/ results Log-normal error structure most closely approximated ADAPT/VPA 1996 and 1997 Fs for fully recruited ages were estimated to be approximately 1.0 Recent recruitment (1994 and 199S year c/asses) poorest ever in both analyses - SSB declining sharply since 1989, remaining lowest ever through 1997 Multinomial model results Bener fit to older ages and slightly lower Fs Lower Fs at older ages In earliest years Slightly lower Fs in recentyears at all ages Slightly better recruitment of 1994 and 1995 year c/asses Marked increase in catchability by the fishery over time Robust likelihood results similar to multinomial, but with very high Fs at older ages since 1988 All model formulations produce results similar to ADAPT/VPA: 1)
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From page 111... ...
= 7,200 t LPUE declined sharply in 1992, remained low in 19931996 Survey Indices remain close to record-low levels in 1995-1996 VPA results ~ VPA results 1996 terminal F for fully recNited ages ranged from 0.96 to 1.04 (essentially 1.0J Recruitment estimates slightly higher when recreational CAA included Recent recruitment (1994 and 1995 year classes) poorest ever in ad nJns Retrospective patterns in recruitment not persistent SSB remains low in all runs Final VPA calibration used commercial CAA alone due to poor sampling of recreational CAA uncertain allocation of recreational cod catch between Gulf of Maine and Georges Bank GuHof Nadine Cod R~h Reco~ons c Fur~erirn~gation of the cam in effort and LPIJEin He V[Rda~setis rec/ui~dbelore [ATE can be Gusto calibrate VPA C hJrff7eri~tigabonof the basis for deriving the renal corm ~ He cod catch, s-:iRcally the effect Quarrying levels in the parkland cf~ catered is required before ff'e renal landings at age can be used to auk He corrrr~al landing at age in He VPA c Furff7er-~r00n oldsc-fags in years pnorto 1989 is required before discards can beir~edi - ~atage 111 current F(1996)
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From page 112... ...
~yan~ sup Inpme carn7eraa, /~ page sari Nine V[R - a for rr~h~fic fiscal was Evaluate changes in my at age in rem .~i Evaluate ~ A die scallop survey as a hr1ir~gin~ Valuate Inks swq~ as a taring index Georges Bank Yellowtail Flounder Assessment Summary F and SSB Trends: - F averaged 1.2 during 1973-1994 and decreased to 0.1 in 1996 - SSB was 21,000 mt in 1973, declined to less than 4,000 mt during 19841988, fluctuated below 6,000 mt from 1989 to 1994, and increased to 11,700 mt in 1996 Probabilitv Distribuffons for F and SSB in 1996: - 80% chance that F was between 0.08 and 0.14, and nearly 0% probability that F exceeded FO.1 (0.25) - 80% chance that SSB was between 9,800 and 14,600 mt, and 12% probability that SSB was below the rebuilding threshold of 10,000 mt and Diagnostics similar among all sensitivity runs.
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From page 114... ...
GB Yellowtail is near SSB Threshold, but SSB for all Stocks is LOW relative to Historical Levels & BMSY Recruitm ent in Recent Years Rem ains LO W R e la tiv e to H is to ric L e v e Is Short-Term Projections Indicate Maintenance or M o d e s t In c re a s e s in S S B a t C u rre n t F s , E x c e p t for GM Cod Strong Managem ent Measures Are Warranted for GM Cod to Reduce the Risk of Stock C o lla p s e Continued Rebuilding of Four Stocks Will Be Jeopardized if Fishing Mortality Rates Are A Ho w ed to In crease Efforts to Reduce F for GM Cod Should NOT Com e at the Expense of Other Heavily Exploited Stocks in the Gulf of Maine or Elsewhere
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From page 115... ...
9 8 1 . 0 0 SNE Yellowtail 10 0.94 1.00
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