Graduate Thesis Or Dissertation


Seasonal life history of Oncorhynchus mykiss in the South Fork John Day River Basin, Oregon Public Deposited

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  • Understanding seasonal changes in growth, survival, and movement rates is crucial to salmonid management. These life history characteristics provide a context for evaluation of management actions. We evaluated the life history of individually marked Oncorhynchus mykiss gairdneri in the South Fork John Day River basin in Northeastern Oregon. This thesis focuses on Murderers and Black Canyon creeks, two tributaries to the South Fork John Day. These are semi-arid, mid elevation basins with naturally reproducing populations of summer steelhead and redband trout (both O. mykiss). Summer steelhead populations in this basin have declined from historic abundances, and are protected under the Endangered Species Act. In Chapter 2, we evaluate life history variation in Murderers Creek during four consecutive seasons. Growth rate varied significantly with season (F[subscript 3,88] = 62.56, P < 0.0001), with most growth occurring during spring. Location and season interacted F[subscript 6,88] = 4.45, P < 0.001) to influence individual growth rates. As a result, regions of high growth potential shifted up and down-stream seasonally. However, we found low rates of O. mykiss movement (<3%) in Murderers Creek during summer, suggesting that individuals did not track resource availability at a large scale. Apparent survival rate varied among reaches, but was consistently higher in the upstream most reach compared to the two lowermost reaches. Survival rates were similar between summer and fall, indicating that declining fall temperatures did not increase mortality. A shift in population distribution occured during fall (September through December), as some O. mykiss emigrated from tributaries into the mainstem South Fork John Day River. In Chapter 3, we investigate differences in fall life history between and within tributaries. A significantly greater proportion of O. mykiss emigrated from Murderers Creek compared to Black Canyon Creek during two consecutive years (P < 0.001 for both years). There were no significant differences in proportion of emigrants between years within either stream (P > 0.10 for both streams). In Murderers Creek, odds of emigration were related to stream reach of summer residence. Odds of fall emigration were also significantly and positively related to body length in fall and growth rate during summer. This suggests that competitive dominants volitionally emigrated from Murderers Creek during fall. After emigration, O. mykiss dispersed primarily further downstream into the Mainstem John Day River. Radio-telemetry indicated that the majority of fall emigrants occupied a < 6 km section of the Mainstem John Day River. Fall emigrants had growth rates during their winter niche shift that were significantly (P < 0.001) higher than those of individuals remaining in tributaries. This study underscores the need to monitor during all seasons to accurately characterize habitat quality. Life history patterns are an important population response to environmental change. This thesis provides an ecological context for monitoring recovery of O. mykiss populations in the South Fork John Day River basin.
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