Plankton effect on forage fish production in the Northwest Atlantic

枯竭的海洋生态系统数量众多，代表着世界海洋中巨大的未实现的渔业生产力。在西北大西洋，尽管实行了20年的禁渔期，但大西洋鳕鱼的多个种群仍未恢复。与20世纪90年代初纽芬兰沿海沃茨鳕鱼和其他底栖鱼数量减少的同时，毛鳞鱼（一种小型饲料鱼，传统上占成年鳕鱼饮食的50-60%）的数量也迅速下降并稳定在低水平。饲料鱼生产持续缺乏被认为是阻碍底层鱼类种群恢复的一个重要因素，与其他亚北极海洋的动态相比，这种情况是反常的。至于大多数海鱼，毛鳞鱼的补充取决于其幼鱼和幼鱼的生存。在生命早期的存活率在很大程度上取决于新出现的幼虫和他们的浮游动物猎物的共同出现。在纽芬兰沿海沃茨，长期的浮游动物数据显示，毛鳞鱼的下降与占主导地位的桡足类物种的丰度减少相吻合。我的研究计划旨在了解幼虫摄食生态学，以测试“浮游生物效应”的假设，保持早期生存和招聘的毛鳞鱼在低水平，从而限制底栖鱼恢复。具体目标包括：（1）定量研究毛鳞鱼幼鱼生活史的食性变化，并分析其偏好猎物可获性年际波动的影响：（2）确定捕食可获性、摄食成功率和幼鱼生长之间的功能反应关系;（3）利用渔业声学评估幼鱼存活的丰度和分布，以及（4）模拟幼虫生长以预测在广泛的环境条件下的存活。由于毛鳞鱼在将能量转移给大型脊椎动物捕食者（如大西洋鳕鱼）方面发挥着关键作用，并可能限制底栖鱼类种群的恢复，因此本研究将通过量化影响加拿大一些最具社会和经济重要性的渔场当前低生产力的机制，填补一个关键的知识空白。将开发的数值模型将有助于预测这些重要的海洋生态系统对未来气候趋势的反应，从而使业界、管理人员和决策者了解西北大西洋食物网中推动生物生产和渔业产量的主要因素。

Depleted marine ecosystems are numerous and represent tremendous unrealized fisheries productivity in the World Ocean. In the Northwest Atlantic, multiple Atlantic cod stocks have still not recovered despite twenty years of fishing moratoria. Coincident with the collapse of cod and other groundfish in coastal Newfoundland waters during the early 1990s, populations of capelin, a small forage fish that traditionally contributed 50-60% of adult cod diet, also rapidly declined and stabilized at low levels. This continued lack of forage fish production, considered an important factor preventing the recovery of groundfish populations, is anomalous in comparison to the dynamics of other sub-Arctic seas. As for most marine fish, recruitment of capelin depends on the survival of their larvae and juveniles. Survival rates during early life are largely determined by the co-occurrence of emerging larvae and their zooplankton prey. In Newfoundland coastal waters, long-term zooplankton data revealed that the decline of capelin coincided with reduced abundance of dominant copepod species. My research program aims at understanding larval feeding ecology to test the hypothesis of a "plankton effect" maintaining early survival and recruitment of capelin at low levels, thereby limiting groundfish recovery. Specific objectives include: (1) quantifying life history shifts in diet of young capelin and characterizing the effects of interannual fluctuations in the availability of preferred prey; (2) determining the functional response relationships linking prey availability, feeding success and growth of larvae; (3) assessing the abundance and distribution of juvenile survivors using fisheries acoustics, and (4) modeling larval growth to predict survival in a wide range of environmental conditions. Since capelin play a key role in transferring energy to large vertebrate predators such as Atlantic cod and may limit the recovery of groundfish populations, this study on the links between secondary production and larval survival will fill a key knowledge gap by quantifying the mechanisms influencing the current low productivity of some of the most socially and economically important fisheries grounds in Canada. The numerical models that will be developed will help forecast the response of these important marine ecosystems to future trends in climate, and will thereby inform industry, managers and policy makers about the primary factors driving biological production and fisheries yield in Northwest Atlantic food webs.