Effectiveness of a Stock Enhancement Program Evaluated by a Two-Stage Sampling Survey of Commercial Landings

In this study, we evaluated the effectiveness of fish stock enhancement programs using a two-stage random sampling survey of commercial landings. Estimators for the total number of fish landed, the ratio of the number of fish released to the total number of fish landed, the recovery rate, and the amount of income were formulated. Variance formulas for these estimators were also derived. In a case study of the flounder fishery, we obtained the conservative estimate of 36 982 recoveries from 246 300 hatchery-reared fish over 3 yr after release. The ratio of the recovery rate to the number of fish released was 0.15. The total income and benefit estimate were $260 000 and $63 000 (U.S.), respectively. We found that the stock enhancement program was economically profitable. We also studied several sampling strategies. We recommend that as many markets as possible be surveyed for a minimum number of days because the variation in daily landings among markets was larger than that within markets. Stratification of markets should be conducted for accurate estimation.