Modification of DeLury's method for a fishery exploiting two stocks.

SUMMARY: This paper proposes a method for estimating stock abundance for a fishery exploiting two stocks, using a model of stock dynamics incorporating effort allocation. We assume that the fishery selects a target stock every hour of operation from the two stocks with a certain probability (α), and that the spatial distribution of stock is either regular or aggregated. The parameters are estimated by the maximum likelihood procedure. Our model is applied to the data of the diving fishery from 1972 to 1976 which catches abalone and top shell along the coast of Toji in Shizuoka Prefecture. The minimum Akaike Information Criterion (AIC) supported the model that the α values were changed between- and within-year. The coefficients of variation of the abundance estimate for abalone ranged from 0.01 to 1.37, and for top shell from 0.01 to 0.03. The abundance estimates were compared with those by the DeLury’s method. The modifications of the model are discussed.