| Summary: | 碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 101 === The oilfish (Ruvettus pretiosus), which widely distributed in the tropical and temperate waters of the world, is one of the bycatch species of the Taiwanese longline fishery in the Indian Ocean. In recent years, the catch of oilfish in the Indian Ocean substantially increased and outnumbered the catch of traditional target species. In this study, we aggregated the fishery statistics data of Taiwanese longline fishery and the data of environment factors, including sea surface temperature, sea surface salinity, sea surface Chlorophyll-a, Indian Oscillation Index and Dipole Mode Index during 2007-2010, to conduct the correlation analyses between catch rate and environmental factors. The Generalized linear models (GLM) and the Generalized additive models (GAM) were also used to explore the relationship between catch rate and environmental factors. In addition, the predicted catch rates estimated from GLM and GAM were used to analyze the temporal-spatial relationship between distribution of catch rates and the environmental factors.
The GLM and GAM results show that the sea surface temperature and the sea surface Chlorophyll-a were the main factors in relation to the distribution of CPUE of oilfish, and the results of GAM model shows that when the environmental factors on the sea surface temperature lower than 20°C, the sea surface salinity distribution in 35.4-35.6 psu, the sea surface Chlorophyll-a concentration in 0.3 mg m-3 in these situation had higher CPUE. CPUE increases with positive value of the Indian Dipole Mode Index and this indicates that the CPUE of oilfish is higher when the sea water temperature in the western Indian Ocean is higher than that in the eastern Indian Ocean. During the full moon phase, catch rate would decrease to the lowest value. The distribution of high catch rate changes with the strength of the cold or warm water mass, moves along the higher gradient of salinity and stands in the waters with higher sea surface Chlorophyll-a. In addition, monthly gravity of fishing ground moves east-westward in the waters off South Africa.
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