Life histories of juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Columbia River estuary as inferred from scale and otolith microchemistry Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zs25xd72t

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  • Despite evidence that juvenile Chinook salmon (Oncorhynchus tshawytscha) utilize North Pacific estuaries for growth and salinity acclimation, research in the Columbia River estuary has lead to opposing hypotheses about the estuary’s importance as a salmon rearing environment. Many contemporary tagging studies indicate that salmon residency within the estuary is short (< 1 week) and that mortality of estuarine migrants is a significant impediment to recovery of depressed salmon stocks. On the other hand, life history interpretations from fish scales collected early in the twentieth century suggest that juvenile Chinook salmon reared extensively in the estuary, leading some to hypothesize that life history variation has been constrained by anthropogenic changes in the Columbia River basin. To test these hypotheses we first validated previous methods of life history interpretation by comparing the results of otolith chemistry, scale chemistry, and scale morphology from juvenile salmon collected during monthly beach seine surveys in 2003. Although scale and otolith chemistry were strongly correlated, and scale chemistry was an accurate indicator of salt-water entry, scale morphometric characteristics did not coincide consistently with the time of salmon entry into brackish water. We measured Strontium 86 and Calcium 43 in salmon otoliths collected in the lower Columbia River estuary in 2003-05 to quantify the period of salt-water residency of juvenile salmon and to back-calculate their size at salt-water entry. The estimated salt-water residency of juvenile Chinook ranged from 0-176 days with a mean residence time of 54, 67 and 30 days in 2003, 2004 and 2005, respectively. Chinook salmon that resided in salt water for more than 30 days comprised 55, 51 and 30% of the total estuary beach seine collections during each of these years. Forty to fifty percent of Chinook salmon had entered the saline portion of the estuary at a fork length < 60 mm. Furthermore we found a negative relationship between the size and time of entry with residency, where smaller earlier migrants on average resided for longer periods then larger late migrants. Peak migration times occurred in May, and 90% of the outmigration was completed by August 30 in all years. This pattern is substantially truncated relative to the results of a 1914-1916 salmon life-history survey, which showed that the historical outmigration period lasted well into the fall and was characterized by late pulses of new recruits into the lower estuary. Nonetheless, recent otolith results indicate that subyearling Chinook salmon use the saline portion of the estuary in a high proportion and for extended periods of time in contrast to short residency times reported by contemporary tagging and marking studies.
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