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UBC Theses and Dissertations

Alternative harvest strategies for Pacific herring Hall, Donald Lincoln


A simulated Pacific herring population (Clupea harengus pallasi) is used to evaluate alternative management strategies of constant escapement versus constant harvest rate for a roe herring fishery. The biological parameters of the model are derived from data on the Strait of Georgia herring stock. The management strategies are evaluated using three criteria: average catch, catch variance, and risk. The constant escapement, strategy provides highest average catches, but at the expense of increased catch variance. The harvest rate strategy is favored for large reductions in catch variance but only a slight decrease in mean catch relative to the fixed escapement strategy. The analysis is extended to include the effects of persistent recruitment patterns. Stock-recruitment analysis suggests that recruitment deviations are autocorrelated. Correlated deviations may cause bias in regression estimates of stock-recruitment parameters (overestimation of stock productivity), and increase in variation of spawning stock biomass. The latter effect favors the constant escapement strategy, which fully uses persistent positive recruitment fluctuations. Mean catch is depressed for the harvest rate strategy, since the spawning biomass is less often located in the productive region of the stock-recruitment relationship. It is recognized that management agencies never have perfect information. Management observation error is modeled as uncertainty in spawning biomass estimates, based on data for errors in the measurements of spawn length, width and egg layers. Mean catch is reduced for both strategies. Reductions in the constant escapement strategy are more pronounced, and vary with the assumed form of the assessment error probability distribution.

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