北大西洋大青鲨种群统计分析

Demographic analysis of the blue shark,Prionace glauca,in the North Atlantic Ocean

大青鲨是金枪鱼延绳钓渔业中最主要的兼捕鱼种,在海洋食物网中属于顶端物种,在海洋生态系统中处于重要地位.由于数据限制,传统的资源评估方法很难准确描述大青鲨的资源动态.本研究基于大青鲨的生活史参数,应用种群统计分析法评估大青鲨的种群参数和资源状态,并探讨了内禀增长率为0时对应的临界捕捞死亡系数Fc与开捕年龄tc的关系.结果表明：未开发状态下,大青鲨存活率为0.719～0.820;大青鲨的内在瞬时增长率（r0）为0.250～0.381,种群倍增时间（t（x2））为1.819～2.773年,种群的净繁殖力（R0）为6.600～22.255,世代间期时间（G）为8.498～10.162年,种群资源状态良好.生活史参数的敏感性检验显示,大青鲨初始年龄的自然死亡系数、种群性成熟年龄及寿命的不确定性对种群统计参数的意义影响不大;临界捕捞死亡系数伴随开捕年龄的增大而增大,当tc≥5时,Fc值与tc无显著相关关系.

The blue shark, Prionace glauca, is the main by-catch species in tuna longline fishery. As one of top species in the oceanic food webs, the blue shark plays an important role in the marine ecosystem. Traditional stock assessment methods are difficult to accurately evaluate the population dynamic for this shark because of limited data. Based on life-history parameters of the blue shark in the North Atlantic, demographic analysis was employed to estimate the demographic parameters and evaluate the potential exploitation for the blue shark. Moreover, we discussed the relationship between age at first capture and critical value of fishing mortality corresponding to the value of intrinsic rate of natural increase 0. The results showed that the survival rate （S） of blue shark from 0.719 to 0.820, intrinsic rate of natural increase （r0） from 0.250 to 0.381, time of population doubling （tx2） from 1.819 to 2.773 years, reproduction rate per generation （R0） from 6.600 to 22.255, and generation time （G） from 8.498 to 10.162 years. The sensitivity analysis for the life history parameters revealed that the uncertainties of natural mortality existed in the first age class, age at maturity and maximum age had slight influence on the demographic parameters. Fishing mortality （Fc） increased with the age at first capture. When the age at first capture （tc） was more than five, there was no obvious relationship between Fc and tc.