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Forecast of the Pacific herring biomass in Togiak district, Bristol Bay, 1993. Regional Information Report 2A93-42. Alaska Department of Fish and Game, Juneau, Alaska.
Abstract and Figures
The 1992 Togiak District spawning migration consisted of 483 million Pacific herring Clupea pallasi weighing 156,955 tons. A total of 27,756 tons were harvested by the inshore sac roe fishery and Dutch Harbor food and bait fishery. The 1993 forecast represents the first year an age-structured analysis, using fishery and run biomass age compositions with selected years of good aerial surveys, was used to generate abundance estimates. The 1993 spawning biomass of herring in the Togiak District is forecast to be 148,786 tons. An estimated 73% of the individuals and 62% of the biomass will be age-5 and -6 herring. The average size of an individual is expected to be 267 g. The 1993 recommended total allowable harvest is 29,757 tons and represents 20% of the forecasted run biomass. In accordance with the Bristol Bay Herring Management Plan, the allocation would be 1,500 tons of herring for the Togiak spawn-on-kelp fishery, 1,978 tons for the Dutch Harbor food and bait fishery, and 26,279 tons for the Togiak sac roe fishery.
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This paper presents a new comprehensive growth model which includes numerous historical models as special cases. The new model is derived from a concise biological principle which, unlike earlier theories, relates to growth acceleration. Properties of growth curves, such as asymptotic limits or inflection points, are shown to be incidental in this new context. Possible submodels include not only asymptotic growth (such as von Bertalanffy, Richards, Gompertz, or logistic growth) but also linear, quadratic, or exponential growth. By simple analysis of variance, the observed data can be used directly in deciding which type of model is most appropriate. The new model is cast in terms of parameters which have stable statistical estimates. From this perspective, it is shown how earlier formulations sometimes result in an endless computer search for optimal parameter estimates.Key words: Growth, asymptotic growth, von Bertalanffy, Richards, Gompertz, logistic, length at age, weight at age, nonlinear parameter estimation
The commercial fishery for walleye pollock (Theragra chalcogramma) in the eastern Bering Sea is the most productive fishery in the United States fishery conservation zone: the total catch exceeded 1 million t in 1982. Historically, this resource has been exploited by foreign distant water fleets; however, there is growing interest among United States fishermen and processors to enter this fishery. Several management strategies have been proposed to facilitate increased domestic participation in this fishery.A bioeconomic simulation was conducted to evaluate the alternative management strategies. The simulation model was an age-structured population model to which economic functions were added. Four alternative fishing regimes were evaluated in the analysis: the current fishery, a fishery directed toward pollock ≳ 36 cm (small fillet), a fishery directed toward pollock ≳ 46 cm (large fillet), and a fishery directed primarily toward small (20-36 cm) pollock for fish paste (surimi). Each fishing regime was simulated over a 20-year period. To account for stochastic variation in the recruitment function, each fishing regime was repeated five times.Results of the simulations indicated that maximum yields of 2.1-2.5 million t can be harvested from the eastern Bering Sea, nearly twice the current level of harvest. The greatest yield was from the fishery for pollock ≳ 46 cm at 2.5 million t and the least, 2.1 million t, from the surimi fishery. The fishing effort required to harvest at these levels was 60-767% greater than current levels. In economic terms, pollock are currently underutilized, but economic maximum yields are much less than the biological maximum. To achieve maximum cumulative discounted profit, effort should be 67% greater than the current level for all of the regimes except the fishery for pollock ≳ 46 cm; here, a maximum is achieved with a fishing mortality 33% greater than the current level. The fishery regime that the simulations indicated provides the greatest cumulative discounted profit is the current fishing regime at a harvest of 1.9 million t, followed by the surimi and small fillet fisheries at 1.7 million t, and lastly the large fillet fishery at 1.2 million t.
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