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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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