CPUE standardization of swordfish (Xiphias gladius) caught by Taiwanese large scale longline fishery in the Indian Ocean

This paper briefly describes historical patterns of fishing operations and swordfish catches caught by Taiwanese large scale longline in the Indian Ocean. The cluster analysis was adopted to explore the targeting of fishing operations. In addition, the delta-gamma generalized linear models were selected to conduct the CPUE standardizations of swordfish caught by Taiwanese large scale longline fishery because large amounts of zero catches existed in the data sets, which resulted in skewed distributions for nominal CPUE. The results indicate that the effects of targeting (clusters) provided most significant contributions to the explanation of the variance of CPUE for the models with positive catches, while the catch probability might be mainly influenced by the latitude of fishing operations. The standardized CPUE series revealed different trends by areas but they obviously increased in recent years except for the Area SW.