碩士 / 國立臺灣海洋大學 / 海洋資源管理研究所 / 94 / The purpose of this study is to assess the stock status of the shortfin mako shark, Isurus oxyrinchus in the Northwest Pacific from 1990 to 2004 based on two methods namely, virtual population analysis, spawning stock biomass per recruit, yield per recruit and stage-based model. Except for Virtual population analysis, these models were applied on females only. Age-specific fishing mortality estimated from VPA indicated an increase of fishing pressure at age of 3 to 6 year for females and 2 to 7 for males since 1996. Spawning potential ratio (SPR) was estimated to be 15.04 % (1996) to 38.48 % (1994) based on deterministic approach and similar results were found from stochastic simulations. These values were lower than the precautionary reference point of SPR=35% since 1995. The 20-year projection from stochastic stage-based model indicated that the abundance will decrease seriously under current fishing effort. The median size of shortfin mako sharks in the commercial catch data has declined since 1996 suggesting growth overfishing and recruitment overfishing is occurring. The above results indicate the population will be collapse under current fishing pressure. The population will maintain equilibrium for the next 20 years if the total allowable catch (TAC) is set at 265 mt, which equivalent to reduce 57% of current fishing pressure. However, close monitoring and modification of the TAC year by year is a necessary measure to ensure the long-term sustainability of the stock.
| Identifer | oai:union.ndltd.org:TW/094NTOU5277004 |
| Date | January 2006 |
| Creators | Jui-Han Chang, 張瑞涵 |
| Contributors | Kwang-Ming Liu, 劉光明 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 136 |
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