Review of Northeast Fishery Stock Assessments (1998) / Chapter Skim
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General Review of Northeast Groundfish Stock Assessments
General Review of Northeast Groundfish Stock Assessments
Pages 25-60
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3. The committee evaluated the Northeast groundfish stock assessments against the NRC ~ 1998)
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26 Review of Northeast Fishery Stock Assessments
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General Review of Northeast Fishery Stock Assessments 27
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28 Review of Northeast Fishery Stock Assessments
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General Review of Northeast Grouncif sh Stock Assessments 29
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The more detailed recommendations follow: Stock definition: Stock identification issues have been considered in the stock assessments, leading to independent assessments for Georges Bank cod, haddock, and yellowtail flounder; Gulf of Maine cod; and southern New England yellowtail flounder; as well as for some 50 other stocks in the general area. It should be noted that the stock boundaries for the U.S.
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being less than 3% for all five stocks. Evaluating Consequences of Alternative Management Actions A primary objective of fish stock assessments is to evaluate the possible consequences of alternative management decisions.
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recruitment will increase in proportion to stock size if spawning biomass is allowed to increase, (2) recruitment will stay constant on average at the historical mean value independent of stock size; (3)
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Similar results, although the stocks did not become extinct, were obtained when recruitment was proportional to stock size. On the other extreme, when recruitment was assumed to be independent of spawning biomass, predicted stock size increased only slightly, since average recruitment was set equalto the average ofthe last ~5 years, which is somewhat higher then the most recent recruitment estimates.
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calibrated to time series of survey catch rates. The data necessary to conduct such analyses are available in the Northeast and are comparable to the data routinely used in stock assessments elsewhere, although Northeast data quantity and quality could be improved.
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Northeast stock assessments use ADAPT in a standard formulation where stock size is estimated by minimizing the sum of squared differences between the natural logarithms of predicted and observed stock size indices. Analyses Included in the Assessment The Northeast groundfish stock assessments include all the analyses expected by the committee: regression analysis to standardize catch rates (when CPUE [catch per unit effort]
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ICES has 19 member nations, conducts marine research in the North AtIantic ocean, and provides scientific advice to member countries. ICES coordinates fish stock assessments and advice through its advisory body, the Advisory Council on Fisheries Management (ACFM)
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More comprehensive stock assessments are carried out when the management procedure is implemented for the stock and when a revised implementation is required (e.g., when area definitions change or alternative management measures are considered)
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More recently, techniques which further reduce fishing mortality at low spawning biomass are being considered to further minimize risk of stock collapse (NRC, ~ 998~. Table 2.2 shows recent estimates of fishing mortality from the stock assessments along with selected biological reference points.
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in Box 2.2. As described above, the Northeast fishery stock assessments contain most of this information.
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. In the early 1990s, NMFS stock assessments suggested that the five stocks had similar characteristics: low spawning-stock biomass (SSB)
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0 15,000 20,000 SSB0ric Tons) 25,000 FIGURE 2.1 Gulf of Maine cod spawning stock biomass (SSB)
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140,000 160,000 180,000 FIGURE 2.3 Georges Bank haddock spawning stock biomass (SSB) and recruitment from original VPA 1965- 1996 SOURCE: NEFSC, 1997a.
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ic Tons) 43 ~ 75 15,000 20,000 FIGURE 2.4 Georges Bank yellowtail flounder spawning stock biomass (SSB)
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The spawning biomass estimate for 1996 is ~ 0,700 tons, compared to 24,500 tons in 1982 (Figure 1.21. ADAPT estimates are not available for years before 1982.
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' Cod (GB) _ \ ~ 0.8 # ~2 0.7 ~ ~ 0.6 2~02k~~ c'` ~ V 0.1 o I \ I \ t- 00 <5 ~0 _ ~00 ~O _ ~ of 00 of 00 00 of 00 of 00 of ~cot ~cot cot ~cry _, ~_ _ _ _ _ ~4 ~_4 ~_ _ _ _ _ _ Year 45 FIGURE 2.7 The ratio of commercial landings to spring survey index spawning stock biomass (SSB)
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As a result, a stock at low spawning biomass will continue to experience low recruitment on average until spawning biomass increases beyond the depensation threshold. These figures show that the trend and amount of uncertainty in future projections depends strongly on which spawner-recruit mode} is used, implications ofthese results were previously discussed in the section "Evaluating Consequences of Alternative Management Actions" (pp.
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49 in .e ~2 -I pi ~ , ,§ I · on - ~ ~ ~ ~ O =~ u ~ e ~ ~ °~ Bi SUOl - + 8 8 8 8 ° BUOY - + ~3 to 04 r 2 2.' .
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so .~ ~f Ip ' ! 11 ~ to If no ~m colt on :~:~:~:~:~:~:~ :-:: I- :.
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~ 08- ~ 70) Stock Size and Condition CPUE and survey trends from NMFS show that the spawning stock biomass of Georges Bank cod, in 1996, was roughly one-fifth the level of the late 1970s (NEFSC, 1997a, Figures B2, Bib.
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Canadian data also show similarly poor recruitment in the most recent years (Hunt and Buzeta, ~ 997~. This analysis suggests the possibility of depensation at low spawning stock sizes; it also provides support for the hypothesis that larger spawning stocks will result in larger recruitments.
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It appears that the recent small increases in spawning biomass (Figure I.2) are due to lower fishing mortality on the existing biomass; recent recruitments for this stock are low (Figures 2.3, 2.17~.
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? Review of Northeast Fishery Stock Assessments Reductions in effort and implementation of closed areas are consistent with the drastic declines in fishing mortality that emerge from ADAPT runs.
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A / 0_1 ~00 c~ __. l \' '/\ 1 J \ \ 0 r ~oo _ ~r~ oo 00 oo oo oo _ _ _ _ _ 55 ~o ~oo ~o ~ 00 00 a0 00 ~ON _ _ _ _ _ _ Year _ _ _ _ _ FIGURE 2.16 The ratio of commercial landings to spring survey index spawning stock biomass (SSB)
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has consistently produced higher year classes since 1978, perhaps because spawning stock biomass there has been maintained closer to an optimal value. Georges Bank Yellowtail Flounder (NEFSC, 1997a; pp.224-259)
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? On average, larger spawning stock sizes have produced more recruits in Georges Bank yellowtail flounder, and both Canadian and U.S.
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- - - Yellowtail Flounder (SEE) \ `'"~"' V''~: 00 ~O _ ~x ~0 _ cat ~rot oo x oo oo so so so oo oo so cat _ _ _ _ _ _ _ _ _ _ _ _ ~_ _ _ _ _ _ _ Year FIGURE 2.20 Ratio of commercial landings to spring survey index spawning stock biomass (SSB)
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? Spawner-recruit data show that recruitment has been fluctuating without a clear trend over a broad range of spawning stocks, with indications that the most recent years (at low spawning stock biomass)
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Thus, if only the period covered by the assessment is examined, the two most likely recruitment hypotheses are: (~) although strong recruitment is not necessarily associated with the largest spawning stocks but rather with favorable environmental conditions, recruitment will decline if high F is maintained; and (2)
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