Static optimization of yeild per recruit with reproduction and fishing costs

Abstract

On the basis of cohort growth and survival data, yield-per-recruit analysis determines the effect of varying fishing mortality and age of first capture on biomass yield from a cohort. However, it does not account for their effect on reproduction, and hence future recruitment. We present here a method of accounting for the impact of exploitation on recruitment by including its effect on egg production. The values of fishing mortality rate and upper and lower age limits that maximize revenues minus costs of fishing, while holding cohort egg production constant, are determined for a range of values of cohort egg production. From the range of optimal policies that result from different specified values of egg production, a manager can select the policy that reflects the desired degree of conservatism regarding cohort egg production. We show that conditions on age limits imply that an upper age limit will rarely be optimal. The effects on optimal policy of including the cost of fishing and accounting for reproduction are related to the commonly used F 0.1 rule.