Graduate Thesis Or Dissertation


Comparing Migratory Patterns and Survival Between Wild and Wild Fish Surrogate Juvenile Spring Chinook Salmon (Oncorhynchus tshawytscha) Public Deposited

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  • Anadromous salmonid populations in the Pacific Northwest have declined over the past 150 years. In 1999, wild spring Chinook salmon (Oncorhynchus tshawytscha) were federally listed as threatened within the Willamette Basin, OR. Currently, practices to restore wild populations in the upper Willamette Basin involve trapping wild adults at the base of high-head dams and hauling them upstream to historic spawning locations. Their resulting progeny must migrate downstream past the dams, highlighting the necessity of effective juvenile passage. Ideally, studies evaluating downstream juvenile passage structures would use wild fish, but this is often not feasible because of the large number of fish required for reliable estimates. The Wild Fish Surrogate Project at Oregon State University rears juvenile spring Chinook salmon as substitutes for wild-origin fish that are intended to behave similarly to wild ones and emulate wild juvenile migratory phenotypes in the Willamette Basin. We compared survival and movement of wild and wild fish surrogate juvenile Chinook salmon using a combination of PIT-tag detections at interrogation stations and seining recaptures in the McKenzie River Basin. We estimated survival with multi-state Cormack-Jolly-Seber models and compared survival between the two groups through time. Overall, detections and movements of wild and surrogate juveniles were similar, although wild fish surrogates tended to move earlier than their wild juvenile counterparts. Surrogate juveniles had a greater probability of movement within the upper Willamette River Basin compared to wild juveniles. This was likely due to the wild fish surrogates experiencing a novel environment and searching for suitable resources within the river system. Movement both within the upper Willamette River Basin and past Willamette Falls increased as the mean 7-day maximum temperature decreased, reflecting seasonal changes. Apparent survival differed between the two groups, and varied with maximum temperature. Surrogate fish had greater apparent survival at warmer temperatures compared to wild juveniles. This difference may have been a result of surrogate juveniles rearing at warmer temperatures prior to release and also being more likely to move downstream soon after being introduced into the McKenzie River.
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