Distribution and habitat of adult salmon in the Situk River, Alaska: Potential impacts of flooding from Russell Fiord

Abstract

Distribution and habitat of adult sockeye (Oncorhynchus nerka), chinook (0. tshawytscha), and pink (0. gorbuscha) salmon in the Situk River, Alaska, were studied to determine the effects of predicted flooding from Russell Fiord. Over 4,500 sockeye and 122 chinook salmon were tagged at a weir in the lower Situk River between 14 June and 21 August 1988. Surveys were done periodically to estimate the number of adult salmon in the survey area and to determine their habitat use and migration timing from late June to late September. All three species used similar habitat while migrating upstream. Most tagged sockeye salmon (> 90%) emigrated rapidly (median 11.2 days in transit) and steadily from the flood corridor, whereas most tagged chinook salmon (>90%) emigrated more slowly (median = 51.7 days) from the corridor, often holding for days in pools or deep glides. Visual estimates of the number of pink salmon indicated that only about 60% emigrated from the flood corridor. Salmon used a wide range of habitat conditions for spawning, and spawning areas were nearly always segregated by species. Spawning habitat characteristics of sockeye salmon differed significantly from those of chinook salmon. Flooding from Russell Fiord would inundate salmon migration and spawning areas in the Situk River and probably cause a short-term decline in salmon production. Long-term impacts on salmon production are likely to depend on the quality and availability of habitat after the river-channel has stabilized.


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