Survival and behavior of juvenile steelhead trout (Oncorhynchus mykiss) in two small estuaries in Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xs55mf62h

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  • A number of steelhead (Oncorhynchus mykiss) populations are at risk throughout Oregon, including five populations that are federally listed as threatened or endangered. However, little is known about behavior and survival of these fish as they transition from freshwater to seawater. We investigated whether estuarine survival varies on a temporal scale within or between years, on a spatial scale between zones within the estuary, and between basins within the same distinct population segment. We implanted acoustic transmitters on 69 wild steelhead smolts in the Nehalem basin and 70 in the Alsea basin and compared run timing, migration rate, and estuarine residence times between basins. We also measured gill ATP-ase levels and parasite loads in each basin to evaluate the relationship between these indices and migration timing, life history strategy or age of smoltification. In general, only 40-50% of the wild steelhead smolts tagged at upstream smolt traps were detected entering the ocean, although survival was highly variable among years. The majority of "mortality" occurred in the lower estuary near the mouth. Wild steelhead smolts spent a median of 0.72 and 0.83 d in the estuary in the Nehalem and Alsea basin, respectively, in 2009. This research provides a baseline by which we can monitor temporal changes in the survival and behavior of juvenile salmon in the estuary. Such information is vital for monitoring the impact of estuarine restoration and reiterates the importance of the lower river and estuary environment for smolt survival.
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