Seasonal Life History of Oncorhynchus Mykiss in the South Fork John Day River Basin, Oregon
AN ABSTRACT OF THE THESIS OF Ian A. Tattam for the degree of Master of Science in Fisheries Science presented on December 22, 2006. Title: Seasonal Life History of Oncorhynchus mykiss in the South Fork John Day River Basin, Oregon Abstract approved: ______________________________________________ Hiram W. Li 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 (F3,88 = 62.56, P < 0.0001), with most growth occurring during spring. Location and season interacted (F6,88 = 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.
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