Optimum Size Limits for Trout Fisheries

Abstract

Application of conventional stock assessment methods to total catch of sport fisheries give neither optimum size limits nor optimum effort; as size limits decrease and effort increases total yield increases asymptotically. In this study total catch is separated into non-trophy and trophy catch; trophy catch has an optimum with respect to fishing effort. Increasing trophy catch decreases total catch, so to optimize the fishery a value is assigned to each category of catch. Optimum size limits for both conventional and slot limits are examined. A slot limit attempts to increase trophy catch without causing a substantial decrease in total catch. Fish are illegal until they reach some minimum size, then they are legal until they reach a certain size or age. They are then again illegal until they reach a trophy size. The results indicate recruitment age should be the smallest size acceptable to fishermen unless trophy fish have a very high value. With conventional size limits total catch decreases rapidly as age at entry increases and fishing effort decreases. Optimum slot limits are determined; slot limits produce a small increase in trophy catch and do not cause a large decrease in total catch.Key words: slot limits, trout fisheries, sport fisheries management, trophy catch