秋田県象潟地先におけるエゾアワビ漁業管理の一手法について

概要

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Age at the first capture (xc) and the prohibition period of fishing (P) as important resource management measures were studied for abalone Haliotis (Nordotis) discus hannai fishery at the Kisakata fishing ground off the coast of Akita Prefecture. Abalone fishery has a long prohibition period and a knife edge selectivity, so a periodic pulse fishery could be assumed. Abalone was assumed to have a Ricker type or Beverton-Holt type reproduction curve. The biomass yield efficiency of parent stock and the recruitment efficiency that indicates its con-tribution to population were taken as objective functions. The sum of biomass yield efficiency and recruitment efficiency was calculated, and the optimum xc and P were investigated. It was found that the current xc=5.6 yr, and P=1 yr. were not the optima. On the other hand, because abalone is a slow-growing and long life species, time-preference and discount rate are seen to have significant effects in its fishery management. Dynamic optimization method in the Beverton-Holt model for a single cohort and Faustmann formula for multiple cohorts were used to determine the optimum xc and P respectively. Considering the results, fishery situation and market value of abalone, it was concluded that the xc=current xc (5.6 yr.), but P=2 yr. are optimum measures for resource management at Kisakata.