Abstract Stream fish rely on a mix of terrestrial and aquatic prey sources. While the importance of terrestrial invertebrates as a food source for stream fish is well documented, the role of aquatic insects that emerge from the stream as winged adult insects (aquatic winged adults) and return to the stream as prey is less understood. In this study we determined the proportion of total diet for stream-rearing juvenile Coho Salmon (Oncorhynchus kisutch) that is derived from terrestrial and aquatic winged adult invertebrates which enter the stream from riparian habitats and consider how those cross-ecosystem prey contributions vary based on riparian habitat type. Study reaches were identified in three streams within the Kenai River watershed of Alaska that were representative of habitats found throughout the region and riparian vegetation was classified into grass/sedge, shrub and tree types using LiDAR. Juvenile Coho Salmon stomach contents were sampled seasonally in study reaches over a two-year period and ingested invertebrates were identified by taxa, life stage and origin. Our results showed that aquatic winged adult prey contributions to juvenile salmon diet were significantly lower in the grass/sedge study reach, and cross-ecosystem invertebrate prey represented a significantly higher proportion of juvenile salmon diet in the tree study reach. Invertebrate prey in the grass/sedge reach were composed primarily of the larval life stage of aquatic winged adults. These results suggest that change in riparian vegetation from tree/shrub to grass/sedge along Kenai streams as projected by regional climate change models, or that results from anthropogenic modification, will likely lead to lower availability of cross-ecosystem prey for stream fish. Management of riparian buffers along streams to preserve or increase occurrence of trees and shrubs is likely to help mitigate impacts of those possible changes.

中文翻译：

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阿拉斯加三条河流沿岸栖息地的无脊椎动物猎物对银鲑幼鱼饮食的贡献：对环境变化的影响

摘要 河鱼依赖于陆生和水生猎物来源的混合。虽然陆生无脊椎动物作为溪流鱼类食物来源的重要性已得到充分证明，但水生昆虫作为有翅成虫（水生有翅成虫）从溪流中出现并作为猎物返回溪流中的作用却鲜为人知。在这项研究中，我们确定了从河岸栖息地进入河流的陆生和水生有翅成年无脊椎动物的流养幼银鲑 (Oncorhynchus kisutch) 的总饮食比例，并考虑了这些跨生态系统的猎物贡献如何变化河岸栖息地类型。在阿拉斯加基奈河流域内的三个溪流中确定了研究河段，这些溪流代表了整个地区发现的栖息地，河岸植被使用激光雷达分为草/莎草、灌木和树木类型。在为期两年的研究范围内，对幼年银鲑鱼胃内容物进行季节性采样，并根据分类群、生命阶段和来源确定摄入的无脊椎动物。我们的结果表明，在草/莎草研究范围内，水生有翅成年猎物对幼鲑鱼饮食的贡献显着较低，而跨生态系统无脊椎动物猎物在树木研究范围内占幼鲑鱼饮食的比例显着更高。草/莎草河段的无脊椎动物猎物主要由水生有翅成虫的幼虫生命阶段组成。这些结果表明，区域气候变化模型预测的沿基奈溪流从乔木/灌木到草/莎草的河岸植被变化，或人为改造的结果，可能会导致溪流鱼类跨生态系统猎物的可用性降低。沿溪流管理河岸缓冲区以保护或增加树木和灌木的出现可能有助于减轻这些可能变化的影响。