Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 9158
Title: Survival of juvenile coho salmon exposed to sudden water temperature increases
Author/Editor: Theodore H. Blahm, Robert J. McConnell
Publication Year: 1970
Publisher: Bureau of Commercial Fisheries
Contracting Agency: U.S. Environmental Protection Agency.  Columbia River Thermal Effects Study

Two thermal electric plants were proposed for siting on the lower Columbia River coincidental with a national directive to establish water temperature standards for the same waters.  The importance of the fishery and inconsistencies in suggested water temperature standards for the interstate waters of the Columbia prompted the Secretary of the Interior to direct a study that would result in the definition of water temperature criteria for salmonids.

During 1968 and 1969, tests were conducted in the Bureau of Commercial Fisheries laboratory located near Prescott, Oregon to define the effects of water temperature increases on the survival of juvenile coho salmon.

We found that a high percentage of fungus infection was possibly an indirect effect of temperature increases and gas bubble disease.  Although the ultimate lethal level for coho juveniles was previously established in laboratory tests as 25°C, on-site tests at Prescott, Oregon, indicated substantial mortality obviously can occur at water temperatures well below that level if fish are stressed by other environmental conditions.