基于GLM模型的印度洋延绳钓渔业大青鲨钩捕死亡率分析

Evaluating at-haulback mortality of blue shark (Prionace glauca) in the Indian Ocean longline fishery based on GLM model

大青鲨(Prionace glauca)是金枪鱼延绳钓渔业的主要兼捕鲨鱼种类。根据2012—2019年中国金枪鱼延绳钓观察员在印度洋记录的1272次作业的778尾大青鲨数据,运用广义线性模型(generalized linear model, GLM)分析大青鲨的钩捕死亡率(即钩捕上船时死亡个体的比率)和潜在的影响因素。结果表明:大青鲨的总体钩捕死亡率为13.4%,雄性的钩捕死亡率高于雌性;潜在影响因素中,钓钩类型、钓钩大小、个体长度、捕获深度和捕获纬度对钩获时的存活状态具有显著影响,其中钓钩类型和捕获纬度的影响最大;钩型与纬度的交互项、性别与个体长度的交互项对死亡率也有显著影响。使用鹰嘴钩时,纬度越北,死亡率越小;其他3种钩型,纬度越北,死亡率越高。雌性大青鲨的个体越大,死亡率减小;但雄性大青鲨的死亡率与个体大小无明显规律。本研究可为降低大青鲨的钩捕死亡率,促进该海域的资源可持续利用提供科学参考。

The blue shark(Prionace glauca) is a main bycatch shark species in the tuna longline fishery. Based on the data of 778 blue sharks from 1272 fishing sets recorded by Chinese tuna longline observers in the Indian Ocean from 2012 to 2019, a generalized linear model(GLM) was applied to analyze the at-haulback mortality(i.e., the mortality rate when fish was captured and hauled back to the deck) and potential influencing factors of blue shark. The results were shown as follows: The overall at-haulback mortality of blue shark was 13.4%, and the at-haulback mortality of males was higher than that of females. Among the potential influencing variables, hook type, hook size, individual size, capture depth and capture latitude had significant influences on the survival status of blue sharks, and the impacts of hook type and capture latitude were the greatest. The interaction between hook type and latitude, as well as between gender and fork length also greatly contributed to at-haulback mortality. When using olecranon hooks, the more northerly being caught, the lower mortality rate was observed;for the other three hook types, the more northerly being caught, the higher mortality rate was observed. The larger the female blue shark was, the lower the mortality rate was observed;however, there was no clear pattern between the mortality rate of male blue shark and their individual size. This study can provide scientific information for reducing the estimated fishing mortality of blue shark and promoting the sustainable use of resources in this fishery.