Both purse seine and longline fleets exploit yellowfin tuna in the western Pa- cific region. Management options available to achieve the optimal allocation of the yellowfin stock depend on whether purse seiners can con- trol the species mix of their catch by targeting their fishing effort. A fishing strategy to target effort on juvenile yellowfin is discussed, and a supply model based on a revenue maximizing framework is estimated using data of Japanese and U.S. purse seine vessels in Papua New Guinea. The hypothesis of targeting is con- firmed for the more modern U.S. fleet, but not for the more traditional Japanese vessels. (JEL Q22)