| Summary: | Thesis (M.S.) University of Alaska Fairbanks, 2023 Small coastal drainages in southeast Alaska (SEAK) support an exceptionally vast and productive region of anadromous fish habitat. However, streamflow patterns within this region are changing. It is expected that hydrologic inputs to streamflow will shift toward increased rain-water contribution, and that extreme high and low water events will become more frequent. Such changes will likely alter the foraging and growth environment of juvenile salmonids throughout this landscape, yet implications of hydrologic change to juvenile salmonid rearing habitats are poorly understood. Moreover, basic questions regarding streamflow impacts on fish foraging and the relative importance of marine-derived resources (MDR) from spawning to juvenile salmonid growth remain unanswered. In this thesis, I explore how environmental conditions within a small coastal watershed of SEAK influence the foraging and growth patterns of two anadromous juvenile salmonid species. In Chapter 1, I examine how streamflow impacts consumption rates and MDR utilization by juvenile Coho Salmon (Oncorhynchus kisutch) and Dolly Varden (Salvelinus malma), and show that early-season streamflow patterns significantly affect fish foraging, where low flows specifically constrain consumption rates and reduce fish growth. These constraints may have particularly negative impacts on fish growth in years of persistent low water conditions, as they could inhibit later-season access to MDR via gape-limitation. In Chapter 2, I build upon findings of MDR contributions to Coho Salmon growth by showing that Pink Salmon (Oncorhynchus gorbuscha) spawning patterns may confer disparate growth conditions between years. Together, results of these chapters provide mechanistic insights into environmental controls of fish foraging and growth in SEAK watersheds. Moreover, they improve understandings of implications of hydrologic change for anadromous salmonid rearing habitats in SEAK, and addresses flow-foraging knowledge gaps ...
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