Stock assessment of the pelagic thresher shark, Alopias pelagicus in the waters of northeastern Taiwan

• Main Authors: Wen-Pei Tsai, 蔡文沛
• Other Authors: Kwang-Ming Liu
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/57849307504350860232

碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 92 === Abstract A stochastic stage-based model was constructed to assess stock status of the pelagic thresher shark, Alopias pelagicus in the northeastern Taiwan waters. In addition, the spawning per recruit model was used to compare with stage-based results. Based on previous biological information, the life history of the pelagic thresher shark was represented as four stages : neonates ( 0-1 yr ), juveniles ( 1-6 yr ), subadults ( 6-8 yr ), and adults ( 8-30 yr ). The results of stochastic stage-based model indicated that the stock increase apparently ( λ=1.082 yr-1, r=0.079 yr-1 ) by randomly selecting natural mortality rates and proportion of maturity. Furthermore, if the stochastic fishing mortality rate was introduced into the model, the abundance will increase slightly ( λ=1.023 yr-1, 95% C.I.= 0.989~1.054 yr-1 ) and advance 25.5% and 61.6% for 10 yr and 20 yr projections, respectively. Spawning per recruit was estimated to be 41.9%, which was greater than the precautionary reference point at 35% or 40%. All strategies showed that the pelagic thresher shark abundance is stabilized under current condition. However, this model is sensitive to juveniles and adults, which implies that close monitoring on these stages is needed to ensure sustainable utilization of the stock.