Distribution and life history characteristics of lacustrine-adfluvial bull trout (Salvelinus
confluentus) were described in the North Fork Skokomish River Basin (including Lake
Cushman, a reservoir) from 1994 to 1996. Day snorkeling was conducted in the river to
determine initiation of the bull trout spawning migration, abundance of spawners, and
duration of spawning. Declining photoperiod, increased river discharge, and decreased
water temperature appeared to influence timing of migration and spawning. Lacustrine-adfluvial
bull trout typically entered the North Fork Skokomish River in October although
some fish entered as early as May. Mean lengths of spawners consistently increased from
June to December 1996, and early migrating bull trout were shorter than those fish that
entered after river discharge increased in October. The presence of two phases of the
spawning migration may be indicative of two populations spawning in the river. Bull trout
spawned between mid-September and December in the river and tributaries after water
temperatures declined. All spawning occurred at temperatures less than 7.5��C.
Comparisons with studies of other lacustrine-adfiuvial bull trout populations that inhabit
river and reservoir complexes suggested that bull trout exhibit specific migratory strategies
related to local environmental conditions. In the North Fork Skokomish River, changes in
abundance of bull trout, mountain whitefish (Prosopium wilhamsom), cutthroat trout
(Oncorhynchus dark), and rainbow trout (Oncorhynchus mykiss) revealed distinct
temporal segregation among these species. Olympic National Park, a designated
Biosphere Reserve, contains one of the largest remaining areas of relatively pristine habitat
in the range of bull trout. Knowledge of responses of bull trout to changes in river
discharge and temperature from relatively undisturbed systems, such as the North Fork
Skokomish River, may be useful in understanding patterns observed in degraded
environments. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33779 |
| Date | 26 February 1998 |
| Creators | Brenkman, Samuel J. |
| Contributors | Larson, Gary L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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