Reproductive value, harvest value, and impact multiplier as indicators for maximum sustainable fisheries

We studied the optimal age- and season-specific sustainable harvesting policy for a fish population. We assumed that body weight, reproduction rate, and natural mortality of a fish vary with age. By assuming completely age- and season-specific harvesting, we can obtain a new, simple criterion for fishing policy. Fishers should catch a fish of a particular age if, and only if, the current value at that age is larger than the harvest value plus the impact multiplier times the reproductive value. Here the harvest value is the expected yield per individual in the future, the impact multiplier is a shadow price for a laid egg and is constant irrespective of the age of the mother fish, and the reproductive value is the expected number of eggs spawned by a fish after that age. Copyright Springer Japan 1999