Catch Rate Analysis of the Indian Ocean Swordfish from Taiwanese Longline Fishery Using Generalized Linear Model

Abstract

Catch of the Indian Ocean swordfish has been increasing rapidly and stayed at high level since 1990s. Estimation of catch rate of the species is needed in this situation. Catch rate analysis of Taiwanese longline fishery which has been operating seasonal targeting practice in the period and made 40-60% of the overall catch, was conducted in this study using generalized linear model with main factors of year, quarter, area and targeting effect. The target factor was expressed by three indexes in the models and all the results indicated that this factor accounted for the highest amount of residual deviance. Further analysis and discussion was performed using one of the indices-swordfish proportion in the catch. Results from the final model showed that the standardized catch rate of swordfish has been declining since 1987 until 1991 and then increased to the level in early 1980s. But this increasing trend did not stand long which might be owing to continuous high catch, and started to decline again since 1998. For deriving more reliable relative catch rates, some suggestions for further studies were discussed.