Assessing Summer and Fall Chinook Salmon Restoration in the Upper Clearwater River and Principal Tributaries, 1994 Annual Report.

Abstract

This is the first annual report of a five year study to assess summer and fall chinook salmon restoration potential in the upper Clearwater River and principal tributaries, Salmon, Grande Ronde, and Imnaha Rivers. During 1994, the authors focused primarily on assessing water temperatures and spawning habitat in the upper Clearwater River and principal tributaries. Water temperature analysis indicated a colder temperature regime in the upper Clearwater River above the North Fork Clearwater River confluence during the winter as compared to the lower Clearwater. This was due to warm water releases from Dworshak Reservoir on the North Fork moderating temperatures in the lower Clearwater River. Thermal temperature unit analysis and available literature suggest a 75% survival threshold level may be anticipated for chinook salmon egg incubation if spawning would occur by November 1 in the upper Clearwater River. Warm water upwelling in historic summer and fall chinook spawning areas may result in increased incubation survivals and will be tested in the future. The authors observed a total of 37 fall chinook salmon redds in the Clearwater River subbasin. They observed 30 redds in the mainstem Clearwater below the North Fork Clearwater River confluence and seven redds in the North Fork Clearwater River. No redds were observed in the South Fork Clearwater, Middle Fork Clearwater, or Selway Rivers. They observed one fall chinook salmon redd in the Salmon River. They recovered 10 fall chinook salmon carcasses in the Clearwater River to obtain biological measurements and to document hatchery contribution to spawning. Unseasonably high and cold Dworshak Dam releases coinciding with early juvenile fall chinook salmon rearing in the lower Clearwater River may be influencing selective life history traits including growth, smolt development, outmigration timing, behavior, and could be directly affecting survival. During July 1994, discharges from Dworshak Dam increased from a baseline release of 1,300 cfs to a maximum release of 25,530 cfs with an overall temperature depression in the lower Clearwater River exceeding 10 C. With continued Dworshak Dam operations as those documented in 1994, there is potential risk to the continued existence of the endangered fall chinook salmon in the Clearwater River. Additional data and conclusions will be contained in successive years` annual reports.