Stock assessment of albacore, Thunnus alalunga, in the Indian Ocean by surplus production models with a new relative abundance index

Albacore (Thunnus alalunga), harvested mainly by longline, has been productive in the Indian Ocean, The population dynamics of Indian albacore has been analyzed by various assessing models. However, the abundance index used previously showed variety within some extents to result in uncertain measures for the stock status. With respect to the importance of environmental factors in estimating an abundance index, the objectives of the present paper are to standardize catch per unit effort for Taiwanese longline fishery by involving a sea surface temperature in general linear model, and to assess the albacore stock using the estimated abundance index by surplus production models. The results obtained reveal that the standardized catch per unit effort follows closely the fishery and the maximum sustainable yield estimated ranges from 32,168 to 34,910 metric tons and effective fishing effort at maximum sustainable yield ranges from 296 to 313 million standardized hooks for different surplus production models. Therefore, the stock status is evaluated to be in healthy and fully exploited condition; and a close monitoring, still, an intensive analysis using age-structured models is recommended for subsequent studies.