Connecting Tidal-fluvial Life Histories to Survival of McKenzie River Spring Chinook Salmon (Oncorhynchus tshawytscha) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zc77st35f

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  • Chinook salmon returns to the Columbia River basin have declined due to impacts of a growing human population, despite significant mitigation expenditures. Consequently, fisheries managers have become focused on recovery and long-term viability of at-risk populations. A viable population depends, in part, on the connectivity and quality of diverse habitat types salmon require to complete their anadromous life-cycles. The tidal-fluvial Columbia River estuary is one link in this chain of habitats, but was largely over-looked as important Chinook salmon habitat until recently. Habitat restoration projects are underway in the tidal Columbia River estuary with the goal of increasing survival benefits to juvenile Chinook salmon. However, knowledge gaps remain about stock-specific use of tidal-fluvial habitat and tracking these restoration efforts is largely subjective. This study has sought to quantify the importance of tidal-fluvial habitat for a critical population of Chinook salmon, from the McKenzie River in the upper Willamette River Basin. Using otolith micro-chemistry profile analysis, juvenile net growth in the tidal-fluvial Columbia River was back-calculated for 92 natural-origin McKenzie River Chinook salmon across outmigration years 2005 and 2006. All otoliths were sampled from McKenzie River adult salmon to draw inferences about the juvenile life histories of surviving spawners. Mean ± SD net growth in the tidal fluvial estuary for all years was 5.48 ± 5.81 mm for subyearlings and 7.43 ± 8.32mm for yearlings. Differences in mean net growth by juvenile life-history type were not significant despite a prevailing assumption that subyearlings rear longer in estuary habitat than yearlings. Emigration sizes and net-growth estimates were significantly greater for subyearlings in outmigration year 2005 than 2006; there was only suggestive evidence emigration sizes were greater for yearlings in outmigration year 2005 than 2006, and net-growth estimates were similar between years. Sixteen percent (15 of 92) of McKenzie Chinook salmon grew between 10 and 43 mm over approximately 25-100 days in the tidal-fluvial Columbia River. Extended rearing in tidal-fluvial habitat provided an alternate life-history pathway for some yearling (12), fingerling (one), and fry (two) migrants. Subyearlings with intermediate-rearing or migratory life history pathways had greater net growth in tidal-fluvial habitat during 2005 than 2006, and in 2005 environmental conditions were unfavorable to overall salmon productivity. Fixed effects linear regression models suggest tidal-fluvial habitat supports McKenzie Chinook salmon life-history diversity, growth, and size, and therefore likely contributes to population resilience.
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