| Summary: | 碩士 === 國立臺灣海洋大學 === 海洋事務與資源管理研究所 === 99 === The depredation impacts of cetacean and sharks on longline fisfery in Xinkang, Taitung were evaluated based on the 31 logbooks from 12 sampling vessels with a total of 649 operations in the southeastern Taiwan water from October 2009 to December 2010. The impacts caused by cetacean are more serious than those by large sharks in the longline fisheries off southeastern Taiwan waters. The damage rates of cetacean on the longline fisheries estimated to be 19.26% and shark equal to 11.56%, respectively. The depredation rates of cetacean were estimated to be 2.21% in number and 3.23% in weight, which were both significantly higher than those of sharks which are 0.51% in number and 0.47% in weight. The depredation indexes were estimated to be 0.93 and 0.22 per thousand hooks for cetacean and sharks, respectively. Our analysis indicated that cetacean and sharks preferred dolphinfish and yellowfin tuna. The economic loss due to depredation of longline fisheries were estimated by combining logbooks and yield and sale records of longline fisheries in Xinkang. Annual economic loss in Xinkang due to depredations of cetacean and sharks are estimated to be 13.39 and 1.78 million NT dollars, respectively. The economic loss caused by depredations from cetacean and large sharks occupied 4.5% and 0.6% of total revenue of longline fisheries in Xinlang, respectively. The General Linear Models (GLM) were used to analyze the influences of the environmental factors, sightings of cetacean, catch compositions and fishing types on the cetacean depredation. The results suggested that only catch in number of dolphinfish and depth had statistically significant impacts on the cetacean depredation for longline fisheries in Xinkang.
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