| Summary: | 碩士 === 國立臺灣海洋大學 === 海洋事務與資源管理研究所 === 98 === Humans acquire nutrition of animal protein from aquatic products by means of capture and aquaculture. However, the marine fishery resources in the world face the risk of overfishing or depletion: about 78% of stocks have been assessed to be in fully- or over-exploited state. To understand why species changes over time is a central challenge in fisheries ecology and is relevant to fisheries management and conservation. The waters off North Taiwan, located at south of the East China Sea are rich in primary productivity and is one of the important fishing grounds in Taiwan. The annual average production of coastal and neritic fishery in Taiwan was 330 thousand metric tons, of which 44% came from the waters off North Taiwan. In the past three decades, the production of the coastal and neritic fisheries in Taiwan showed a decreasing pattern, while no significant pattern was found in the production from the waters off North Taiwan. In this study, landing data of 16 fishing species from 1976 to 2007 were obtained from fisheries yearbooks to (1) analyze the temporal variation of fishing species composition in landing in the waters off North Taiwan; (2) examine the temporal pattern in landing of fishing species and potential effects by fishing (number of vessels) and environmental factors (Southern Oscillation Index, Sea surface temperature at North Taiwan and river discharge); (3) extract the common trends of landings of fishing species by DFA and explore potential effects of fishing and environmental factors. The results showed that the fishing species composition in landing shift in 1988/89 and 2000/01 which may reflect the effects of Pacific Decadal Oscillation in the North Pacific. The mean trophic level calculated from fishing species composition in landing showed an increasing pattern after 1998, which was caused by the increasing landing of Scomber spp. from the 1990s onward. The optimal DFA model contained three common trends and all of the explanatory variables. The first common trend shows a general increasing pattern from 1976 to 2007, and is positively related to landing of Scomber spp., Auxis rochie, and Pagrus major. The second common trend shows a peak at 1991 and a decrease from 1992 onwards, and is positively related to Trichiurus lepturus, and Nemipterus virgatus. The third common trend shows stable in 1989~2002 and a decrease 2003 onwards, and is positively related to Loliginidae and Pampus argentata. The increasing trend for landings of Scomber spp. and A. rochie could be explained by the decrease of fishing vessels in the 1990s. The decreasing trend for landing of T. lepturus may be related the increase of SST at North Taiwan. The SOI may provide a composite indicator for whole environmental conditions, or affect fishing resources via a lag effect on regional environmental factors.
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