ECOLOGICAL AND ECONOMIC COMPONENTS OF ALTERNATIVE FISHING METHODS TO REDUCE BY-CATCH OF MARLIN IN A TROPICAL PELAGIC ECOSYSTEM

摘要

Recently, the U.S. National Marine Fisheries Service was petitioned to list North Atlantic white marlin as an endangered species under the Endangered Species Act (ESA). The ESA requires a stock assessment of status and trends for listed species and will severely restrict U.S. commercial and recreational fisheries, but because by-catch by foreign longline fleets account for more than 95% of marlin mortality, applying the ESA to U.S. fleets would have little direct effect. We analyzed an alternative management policy by using an Ecosim model of the central north Pacific to simulate a fishing strategy that reduces marlin by-catch by removing longline hooks that fish in water less than 120 m in depth. Mortality rates might be reduced by about 50% through removal of less than 15% of hooks. After 30 yrs, blue marlin biomass had increased to 2.8 times, and striped marlin biomass to about 1.8 times, that expected under no change in fishing practices. Ecological consequences included decreased abundance of adult yellowfin tuna. This result produced an economic trade-off of lost fishery revenues (primarily yellowfin tuna) and gains due to increased catches of billfishes in recreational fisheries.