碩士 / 國立臺灣海洋大學 / 環境生物與漁業科學學系 / 96 / Abstract
Swordfish (Xiphias gladius, Linnaeus 1758) in the Indian Ocean were mainly caught by Taiwanese and Japanese longline fisheries in the early years. Since 1990’s the catch increased substantially due to seasonal targeting of Taiwanese longline fishery and exploitation of Australia, France-Reunion, Spanish and Sri Lankan.
Most previous assessments of swordfish in the Indian Ocean have been based on trends in CPUE and the results of production model assessments. Swordfish are known to be sexually dimorphic and previous assessments ignored the age- and sex- structured dynamics of population. Due to absence of sex-specific information, however, an age-structured assessment model without sex factor was conducted for evaluating the population status of the swordfish in the Indian Ocean.
Based on the results of the base-case analysis, the fleet-aggregated fishing intensity in 2005 was higher than that at which MSY is achieved and the spawning stock biomass in 2005 was about 37% of its unfished level and about 1.88 times of that at which MSY is achieved. The result of the sensitivity analyses indicated that the results of assessment model are sensitive to the values of natural mortality. Nevertheless, the least optimistic results, which indicated that the spawning stock biomass in 2005 was remaining about 27% of its unfished level but still higher that at which MSY is achieved, only occurred when natural mortality was assumed to be a relatively low value. Therefore, the results of this study indicate that there is probable overfishing of the swordfish stock in the Indian Ocean in recent years while the stock currently appears not to be in an overfished state.
| Identifer | oai:union.ndltd.org:TW/096NTOU5451017 |
| Date | January 2008 |
| Creators | Ying-Ru Chen, 陳盈如 |
| Contributors | Sheng-Ping Wang, 王勝平 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 94 |
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