Predation on anadromous salmon can have important consequences for both predators and prey. Salmon provide large seasonal pulses of energy and nutrients via carcasses, eggs and juveniles to many freshwater consumers, and conversely, predation can represent a significant source of mortality for juvenile salmon. Recent declines of Chinook salmon (Oncorhynchus tshawytscha) populations in Alaska have raised concern that predation might inhibit their recovery. Here, we quantify patterns of predation by freshwater fishes on juvenile salmon across seasons, habitats, predator sizes and streamflow levels in the Arctic-Yukon-Kuskokwim region of Alaska. We analysed piscivore stomach contents and identified prey using DNA sequence “barcoding.” In coastal rivers, juvenile pink (O. gorbuscha) and chum (O. keta) salmon contributed heavily to Arctic grayling (Thymallus arcticus) and Dolly Varden char (Salvelinus malma) diets, coho salmon (O. kisutch) prey were rare, and Chinook salmon were not detected. In interior rivers, Arctic grayling, burbot (Lota lota) and northern pike (Esox lucius) consumed small numbers of Chinook salmon. Predation on Chinook salmon was documented disproportionately in sloughs during a summer of exceptionally high streamflow. Dietary and distributional patterns suggested northern pike and burbot may exclude salmon from sloughs in low-gradient river reaches that would otherwise provide suitable rearing habitat. The data also provided tentative support for the hypothesis that high streamflow induces juvenile Chinook salmon to move from mainstem habitats into sloughs, where they face an increased risk of mortality. Incorporating predation risk into climate adaptation, fisheries management and habitat restoration decisions may help to facilitate Chinook salmon recovery.

中文翻译：

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亚北极阿拉斯加河流中对幼鲑鱼的捕食：与季节、栖息地、捕食者大小和流量的关系

捕食溯河鲑鱼会对捕食者和猎物产生重要影响。三文鱼通过胴体、卵和幼鱼为许多淡水消费者提供大量季节性能量和营养物质，相反，捕食可能是幼鱼三文鱼死亡的重要来源。最近阿拉斯加奇努克鲑鱼（ Oncorhynchus tshawytscha ）种群数量的下降引起了人们对捕食可能会抑制其恢复的担忧。在这里，我们量化了阿拉斯加北极-育空-库斯科克维姆地区淡水鱼在不同季节、栖息地、捕食者大小和水流水平上对幼鲑的捕食模式。我们分析了食鱼动物的胃内容物，并使用 DNA 序列“条形码”识别了猎物。在沿海河流中，幼年粉红色（O . gorbuscha ) 和 chum ( O .  keta ) 鲑鱼对北极鳀鱼 ( Thymallus arcticus ) 和 Dolly Varden char ( Salvelinus malma ) 饮食的贡献很大，银鲑 ( O .  kisutch ) 的猎物很少见，而奇努克鲑鱼没有被检测到。在内陆河流中，北极河豚、江豚 ( Lota lota ) 和北梭子鱼 ( Esox lucius) 食用少量的奇努克鲑鱼。在流量异常高的夏季，对奇努克鲑鱼的捕食记录不成比例地出现在泥沼中。饮食和分布模式表明，北梭子鱼和江豚可能会将鲑鱼排除在低坡度河流河段的泥沼之外，否则它们将提供合适的饲养栖息地。这些数据还为这样的假设提供了初步支持，即高流量会导致幼年奇努克鲑鱼从主干栖息地迁移到泥沼中，在那里它们面临更高的死亡风险。将捕食风险纳入气候适应、渔业管理和栖息地恢复决策可能有助于促进奇努克鲑鱼的恢复。