Optimizing Cost-Effectiveness of Size at Release in Stock Enhancement Programs

Abstract

Abstract In this paper, we consider how size at release (SAR)−dependent survival of stocked fish can influence the cost-effectiveness of stocking strategies. Production costs for various sizes of juvenile fish were related to performance based on capture rates in a subsistence fishery in Kaneohe Bay on the island of Oahu, Hawaii. Using production cost data from a small-scale research hatchery, we examined the costs required to rear striped mullet Mugil cephalus to various stocking sizes. A spreadsheet cost model for marine shrimp aquaculture was adapted to striped mullet intensive culture techniques in Hawaii. Costs were calculated for the maturation, hatchery, and nursery phases of striped mullet production based on spawning protocols that reflected conservation of wild-stock genetic diversity. We identified the costs required to rear fingerlings to each of five consecutive size intervals, ranging from 45 to 130 mm total length (TL). Size-dependent postrelease mortality had a significant impact on the cost-effectiveness of stocking strategies. A simple mathematical model was developed to determine the optimal (most cost-effective) SAR for a stock enhancement program that releases striped mullet into Kaneohe Bay. The production-related cost of an enhancement effect (dollars spent in the hatchery to achieve a hatchery fish contribution to the fishery) was least for fish that were 85–110 mm TL when stocked. These kinds of empirical data from pilot hatchery release studies should be factored into decisions about the sizes of fish released in stocking programs.