Analysing environmental and fishing effects on a short-lived species stock: the dynamics of the octopus Octopus vulgaris population in Senegalese waters

Short-lived species are extremely dependent on the seasonal and interannual variability of environmental conditions, and determining their stock status is often difficult. This study investigates the effects of environmental variability and fishing pressure on the stock of octopus Octopus vulgaris in Senegalese waters over a 10-year period from 1996 to 2005. Monthly catches-at-age were estimated based on catch-at-weight data and a polymodal decomposition constrained by a given growth curve. Octopus recruitments and fishing mortalities were then estimated using a catch-at-age analysis performed on a monthly basis. Yield and biomass per recruit were simulated using a Thompson and Bell model and used to generate a diagnostic of the fishery's impacts. Results indicate that the high interannual and seasonal variability of the octopus stock biomass is linked to the spring recruitment event, the annual intensity of which was significantly correlated with the coastal upwelling index and sea surface temperature. Yield per recruit varied seasonally but remained almost unchanged from one year to the next. Even when catches vary strongly according to recruitment, the octopus stock appears to be consistently fully exploited, or slightly overexploited in some years. In this context of environmental variability, usual indicators such as the maximum yield per recruit, and the related fishing mortality and spawning potential ratio, remain useful for fisheries management purposes.     

南海北部海域小型非经济鱼类资源声学评估

为探讨南海北部渔业资源的可持续利用情况 ,根据 1997年 12月～ 1999年 6月“北斗”号调查船SimradEK5 0 0回声探测 积分系统在南海北部海域获取的渔业资源调查资料 ,对该海域天竺鲷科、科、灯笼鱼科、鳄齿鱼科以及犀鳕科等 5类 5 8种小型非经济鱼类进行了资源量评估。结果表明 ,这些种类在南海北部海域具有比较丰富的资源储量 ,它们春、夏、秋、冬 4个季节的平均资源量分别为 18.5× 10 4t,2 6.1× 10 4t,2 2 .3× 10 4t,17.6× 10 4t和 4.5× 10 4t ;分析了其资源量的区域分布和季节变化。     

基于贝叶斯状态空间产量模型的大西洋黄鳍金枪鱼资源评估

黄鳍金枪鱼(Thunnus albacares)是全球远洋渔业的重要目标鱼种,要实现有效的管理,对其进行科学的资源评估是必不可少的。本文以大西洋黄鳍金枪鱼为研究对象,根据国际大西洋金枪鱼养护委员会的渔获量和单位捕捞努力量渔获量数据,使用贝叶斯状态空间模型进行资源评估,并探讨不同剩余产量函数和单位捕捞努力量渔获量数据对评估的影响。结果表明,使用美国、委内瑞拉、日本和中国台北4个船队的单位捕捞努力量渔获量数据及Fox剩余产量函数时模型拟合效果最佳。关键参数环境容纳量和内禀增长率的估计中值和95%置信区间分别为178 (140,229)×10⁴ t和0.210(0.159,0.274);当前资源量为72.5×10⁴ t,最大可持续产量为13.7×10⁴ t时,种群既没有遭受资源型过度捕捞,也没有捕捞型过度捕捞发生。敏感性分析表明,当渔获量数据存在误报率(70%、80%、90%、110%、120%和130%)时,生物量的评估结果偏高,而捕捞死亡率的结果偏低,但种群均处于健康状态;预测分析显示,当总允许可捕量设为11×10⁴ t时,资源在2024年前仍基本保持健康状态。本研究与国际大西洋金枪鱼养护委员会现有的评估结果基本一致,且模型较稳健,可以为管理决策提供建议。根据模型结果,建议总允许可捕量为11×10⁴ t或更低,以使资源达到可持续开发水平。