| Summary: | 碩士 === 國立臺灣海洋大學 === 海洋資源管理研究所 === 95 === An aquatic ecosystems simulated software named Ecopath with Ecosim (EwE) was used to construct a model to represent the pelagic ecosystem in the northwest Pacific. The input of parameters including biological imformation, diet compositions and yields of 17 functional groups, which are the main target species of longline-fishery and their preys, were collected from literatures. The Ecoranger was used to estimate the effects of uncertainties of input parameters. The impacts of longline-fishery and fishery management strategies on this marine ecosystem were simulated with Ecosim function.
In the northwest Pacific pelagic ecosystem, Lamniforms and Carcharhiniforms whose trophic level equal 4.16 are the top predators. The blue shark which has lower trophic level than Lamniforms and Carcharhiniforms is the most abundant large sharks species. The results of Ecosim simulations indicated that Lamniforms and Carcharhiniforms are overfishing. Furthermore, a series of strong and unforeseen changes in the abundances of many species may occur, due to the removal of large sharks from this marine ecosystem. Therefore, a biological reference point of F35% for Lamniforms species was proposed. The scombrids and dolphinfish have the strongest keystone effects because the decrease of Top-down control from top predators, such as large sharks, tuna and swordfish species were heavly removed from the northwest Pacific pelagic ecosystem by longline-fishery. Longline-fishery has positive effects on dolphinfish and marine mammals by removal of both their predators and competitor for preys. But longline-fishery makes negative effects on other target species. Therefore, a decrease of longline-fishery efforts may result in a recovery of large sharks, tuna and swordfish species.
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