Graduate Thesis Or Dissertation
 

Year-class regulation of mid-upper Columbia River spring Chinook salmon Oncorhynchus tshawytscha : the role of juvenile size, growth, and migratory behavior

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  • Early ocean residence is assumed to be a critical period for juvenile Pacific salmon Oncorhynchus spp. However, the specific mechanisms influencing growth and survival in the ocean have not been identified for most populations. Therefore, three hypotheses regarding the relationship between early marine residence and subsequent survival of mid-upper Columbia River spring Chinook salmon were evaluated: the 'bigger is better', 'stage duration', and 'match-mistmatch' hypotheses. Six metrics describing juvenile migration history and condition were developed, including 1) size at freshwater exit; 2) size at ocean capture; 3) initial ocean growth rates; 4) timing of ocean entrance; 5) duration of ocean residence; and 6) marine migration rates. Retrospective estimates of size and growth using otolith analyses rely on the assumption that otolith and somatic size are related. Therefore, I verified this assumption for mid-upper Columbia River Chinook salmon and determined that a body-proportional back-calculation method was the best approach for this population. Fish length and otolith width were positively correlated (r > 0.92) and growth rates estimated from back-calculated sizes were positively correlated with observed growth rates (r = 0.96). I also evaluated the utility of using the otolith Sr:Ca pattern as a marker of hatchery-origin and investigated potential mechanisms for the observed Sr:Ca pattern. Visual and quantitative criteria were developed using otoliths of hatchery fish and were used to correctly classify 85% and 78%, respectively, of a sample of known hatchery-origin fish (n = 114) that were collected in coastal waters. Although Sr:Ca in water and hatchery food did not fully account for the observed pattern in otolith Sr:Ca, the pattern can be used to identify mid-upper Columbia River spring Chinook salmon of hatchery-origin with relatively high accuracy (>75%). The six juvenile metrics were used to evaluate mechanisms potentially regulating establishment of year-class abundance. The only metrics found to be significantly related to future adult abundance were size at freshwater exit (r² = 0.56) and capture (r² = 0.60). These data support the 'bigger is better' hypothesis and indicate that factors influencing size and growth during freshwater residence should be investigated further. Juveniles resided in the brackish/ocean for one to two months prior to capture in May and June; therefore, ocean conditions after this period may be related to the 40% of variation in adult abundance unexplained by interannual variation in body size.
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