Cooperative Fish and Wildlife Research Units Program: California
Education, Research and Technical Assistance for Managing Our Natural Resources

Declining populations of Pacific salmon (Oncorhynchus spp.) in the Klamath River have led to concerns about water quality in the river. Water temperature in the river during summer months often approaches or exceeds physiological tolerance limits of most Pacific salmon species. Reliance of these fish on cold water has been studied extensively. While temperatures at which the physiological performance of Pacific salmon is optimal is typically 14.0 - 17.0 o C, salmon are also frequently are found occupying habitats where water temperatures reach 23.0 - 24.0 o C on a daily basis. Much of the variation in tolerance to warmer water temperature in Pacific salmon is attributed to acclimation temperature. In the Klamath River, water temperature regularly exceeds 25.0 o C during July and August. Pockets of cool water that form at tributary mouths are believed to be critical to the survival of Pacific salmon during these periods. Re-analysis of data gathered by the Yurok Tribe during 1998 confirms use of cold water patches at temperatures > 22.0 o C, but also reveals a strong temporal component in use. Furthermore, spatial distribution of refuges having high abundance (> 1000 juvenile Chinook salmon) are clumped at a few stream mouths. The periodicity in heavy use of cold water patches by Chinook salmon and their spatial clumping at limited sites suggest that habitat selection is governed by more than water temperature alone. The objectives of this study are: 1) To determine if juvenile Chinook salmon and steelhead use cold water patches in the Klamath River preferentially over other habitats. 2) To determine if juvenile Chinook salmon and steelhead use specific cold water patches in the Klamath River for extended periods or for short periods during migration. 3) To determine the physiological benefit of cold water refuges to juvenile Chinook salmon and steelhead in the Klamath River.