A New Assessment Approach Using Fuzzy Surplus Production Model to Evaluate the Albacore Stock in the Indian Ocean

Abstract

Albacore is one of the important temperate and productive species. Since 1970s, Taiwan has been the leading nation exploiting the species using longline in the Indian Ocean (about 85% total annual catch). For assessing the stock status, a traditional Schaefer surplus production model and a fuzzy surplus production model are used for this purpose. Daily catch and effort data extracted from logbooks from 1979 to 1997 of Taiwan tuna longline fishery is used to derive the abundance index that is standardized by the general linear model with year, month, subarea and target species factors. The annual catches from longline and surface gears were used to fit these production models. The results show that a standardized abundance index was obtained with fluctuated stably in a high level from 1979 to 1987 then decreased from 1988 to 1995, and increased after 1995. The maximum sustainable yield (MSY) estimated by Schaefer production model is 27,717 mt. The MSY estimated by fuzzy surplus production model ranged from 25,728 to 30,651 mt with increasing vagueness and point estimated at 27,248 mt. Since 1992, the catches have been far below MSY, indicating that the stock may be under exploited status and an optimistic projection with a current catch level may be resulted from the increasing abundance index trend and catch level under MSY.