热带东太平洋中上层鲨鱼的生态角色及对系统结构和功能的调控机制

Pelagic sharks are vulnerable to overfishing due to their slow growth rates, late age-at-maturity and low fecundity. Currently, 90% of pelagic shark species are Near Threatened with an elevated risk of extinction according to IUCN Red List Criteria. Comparing with their nearshore relatives, pelagic sharks are opportunistic generalist predators. It is still under debate whether their ecological roles in the open ocean are indispensable or functionally redundant. The knowledge on feeding habits and behaviors of pelagic sharks and the impacts of their removal on community structure were also unclear, which have hampered their effective conservation. In this project, the ecological roles of pelagic sharks in the Tropical Eastern Pacific will be explored. Based on the non-lethal sampling, gut content analysis and the applications of multiple biogeochemical tracers, the feeding ecology of pelagic sharks will be studied, as well as the predation risk effects. Their ecological niche partitioning, interaction intensity and the coexistence mechanisms with sympatric large top-predator guilds will be investigated by quantifying the spatiotemporal and trophic niche overlaps among species. Furthermore, the removal effects of pelagic sharks on ecosystem structure and functions under various scenarios and scales will be evaluated, respectively, with the purpose of better defining their unique roles in the Tropical Eastern Pacific. The results will be beneficial to the conservation of biodiversity in the open ocean, be helpful in promoting our national scientific figures, and furthermore, improve our discourse rights on the fishery management in the international Regional Fisheries Management Organizations.

大洋中上层鲨鱼多为金枪鱼渔业的兼捕渔获。因其生长缓慢、繁殖力低等生活史特征，极易被过度捕捞，90%种类已近危。与近海大型鲨鱼不同，大洋性鲨鱼食性更泛化。目前，对其生态功能的关键性和冗余性仍悬而未决，对其摄食习性和行为的了解仍十分有限，对其数量下降可能引发的生态效应仍模糊不清，科学认知的不足严重阻碍了对其资源的针对性保护，亟待解决。本研究聚焦热带东太平洋海域，以鲨鱼为研究对象，采用非致命性取样、胃含物分析及多种生物地球化学标记，量化其捕食者效应；从营养生态位分化及栖息地时空分离两方面入手，量化其与同域捕食者的资源利用程度、方式和竞争强度，进而揭示东太平洋顶级捕食者的生态位格局及竞争、共存机制；构建生态系统模型，模拟食物网结构对鲨鱼缺失的响应变化规律。从个体、种群、群落和生态系统水平系统定位鲨鱼生态功能，为大洋物种多样性保护提供理论支持，且有助于树立我国在渔业管理组织中的科学形象，提升话语权。

大洋中上层鲨鱼多为金枪鱼渔业的兼捕渔获。因其生长缓慢、繁殖力低等生活史特征，极易被过度捕捞，90%种类已近危并被列入《华盛顿公约》附录II，资源利用受到严格监管。与近海大型鲨鱼不同，大洋性鲨鱼食性更泛化，与同属大洋捕食者的金枪鱼、剑旗鱼类存在激烈的资源竞争关系。然而目前，对大洋性鲨鱼生态功能的关键性和冗余性仍悬而未决，对其摄食习性和行为的了解仍十分有限，对其数量下降可能引发的生态效应仍模糊不清，科学认知的不足严重阻碍了对其资源的针对性保护，亟待解决。本项目在完成220天的东太平洋调查航次的基础上，以热带东太平洋大洋性鲨鱼为研究对象，采用非致命性取样、胃含物分析、多种生物地球化学标记（稳定同位素，氨基酸稳定同位素和脂肪酸组成）和多种污染物（Pops、Hg）量化其捕食者效应；从营养生态位分化及栖息地时空分离两方面入手，量化了其与同域捕食者的资源利用程度、方式和竞争强度，揭示了东太平洋顶级捕食者的生态位格局及竞争和共存机制。项目取得了一系列重要的研究成果。首次揭示了营卵胎生生殖方式且胚胎具有食卵性的浅海长尾鲨和营胎盘胎生生殖方式的镰状真鲨在繁殖过程中的母胚间微量元素迁移和稳定同位素值分馏规律；理清了鲨鱼脂质代谢途径，掌握了外源性脂肪酸储存模式及鲨鱼基础生理生态学特征，创新性发现肝脏组织不适于脂肪酸组成分析，血浆和肌肉组织可揭示鲨鱼短期和长期的摄食信息。通过直接观察脊椎骨轮纹，进行年龄鉴定，建立各物种生长方程，估算最适生长参数，并基于微取样微化学技术，初步探明了大洋性鲨鱼生活史过程中食性转变和栖息地变化的辩证关系，发现了大洋性鲨鱼食性泛化度高，食性转变不明显、栖息地多且复杂化的特点，可能与其高度洄游性且对多种深度的适应性有关。项目从个体、种群、群落和生态系统水平系统定位鲨鱼生态功能，为大洋物种多样性保护提供理论支持，且有助于树立我国在渔业管理组织中的科学形象，提升话语权。