Abstract Marine growth and survival of juvenile Pacific salmon (Oncorhynchus spp.) have been linked to marine temperatures and feeding conditions during their first few months at sea. Therefore, understanding what salmon consume under varying environmental conditions is important to understanding how their growth and survival are affected by climate change. Here, we examined how warm/cool-phase variation in water temperature, salinity, wind speed, and pycnocline depth influenced the diet composition and quality of four species of juvenile Pacific salmon in Icy Strait (Southeast Alaska) from 2013 to 2017. During the five-year period, water temperatures shifted from a cool phase in 2013 to warm in 2014–2016, then back to cool in 2017. Overall, the diet composition and prey diversity varied among zooplanktivorous species (pink salmon O. gorbuscha, chum salmon O. keta, and sockeye salmon O. nerka) and piscivorous (coho salmon O. kisutch) species, with the exception of 2015, when euphausiids were the dominant prey for all four species. The summer of 2015 was notable for its deep pycnocline although it was not the warmest year in the study. Zooplankton nutritional quality was below average in 2015, but lipid intake by juvenile salmon appeared to be supplemented by the availability of larger euphausiid prey. Across years for all species, diet composition was weakly correlated with a combination of water temperature, salinity, and wind (Pearson correlation = 0.216). We conclude that while the marine heat wave altered the Gulf of Alaska ecosystem, within the range of variability observed during the study period, juvenile salmon were able to meet their energetic demands by switching to alternative prey.

中文翻译：

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幼年太平洋鲑鱼对阿拉斯加东南部海域内暖冷时期的营养反应

摘要 太平洋鲑鱼幼鱼 (Oncorhynchus spp.) 的海洋生长和存活与它们在海上最初几个月的海洋温度和摄食条件有关。因此，了解鲑鱼在不同环境条件下消耗的食物对于了解气候变化如何影响它们的生长和生存非常重要。在这里，我们研究了 2013 年至 2017 年冰冷海峡（阿拉斯加东南部）的四种太平洋鲑鱼幼鱼的饮食成分和质量，其中水温、盐度、风速和旋斜深度的暖/冷相变化如何影响。五年期间，水温从 2013 年的凉爽阶段转变为 2014-2016 年的温暖阶段，然后在 2017 年恢复凉爽。总体而言，食浮游动物物种（粉红鲑鱼 O. gorbuscha、鲑鱼 O. keta 和红鲑鱼 O. nerka）和食鱼（银鲑鱼 O. kisutch）物种，但 2015 年除外，当时磷虾是所有四种物种的主要猎物。2015 年的夏天因其深部的火山灰倾角而引人注目，尽管它并不是研究中最温暖的一年。2015 年浮游动物的营养质量低于平均水平，但幼鲑鱼的脂肪摄入量似乎得到了更大的磷虾类猎物的补充。在所有物种的年份中，饮食成分与水温、盐度和风的组合呈弱相关（Pearson 相关系数 = 0.216）。我们得出的结论是，虽然海洋热浪改变了阿拉斯加湾的生态系统，但在研究期间观察到的变化范围内，