Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 6562
Title: Effects of 1985-1986 levels of dissolved gas on salmonids in the Columbia River
Author/Editor: Earl M. Dawley
Publication Year: 1986
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: DACW57-85-F-0623
Pages: 34
Date: 11/01/1986

In the 1980s, a program of increased spill at dams was implemented to improve passage of juvenile salmonids.  This created diurnal fluctuations of supersaturation within the river system.  The U.S. Army Corps of Engineers and the National Marine Fisheries Service began to reevaluate the effects of current dissolved gas levels on salmon in the Columbia River system, including fluctuating supersaturation caused by designated spill for fish.

In 1985, a field bioassay and monitoring program was established to evaluate the impacts of intermittent high supersaturation on both juvenile and adult salmonids.  The reservoir of The Dalles Dam (rkm 308) was selected as the primary evaluation site because daily spill was expected at John Day Dam (rkm 347).  In the 1970s, spill at John Day Dam created the highest dissolved gas levels in the river system, and in the 1980s, high dissolved gas levels resulting from intermittent spill were observed in the forebay of The Dalles Dam.

The objectives of the bioassay and monitoring program were:
1.  To obtain daily dissolved gas concentrations in the forebays of John Day and The Dalles Dams.
2.  To observe and record signs of GBD in juvenile and adult salmonids sampled at various sites on the river.
3.  To determine the migration rate of marked fish passing through The Dalles Dam reservoir.
4.  To conduct holding studies with juvenile spring and fall chinook salmon, of hatchery and river-run stock, in The Dalles Dam forebay and examine depth distribution in relation to level of supersaturation.
5.  To obtain depth distribution information for juvenile salmonids in the forebay of The Dalles and John Day Dams using hydroacoustics.
6.  To assess the probable effects of dissolved gas supersaturation on salmonid migrants and compare the results with information obtained in the 1960s and 1970s.

During 1985 and 1986, the impacts of supersaturation were minimal to juvenile and adult salmonids in the lower Columbia River from McNary Dam to the estuary.  Juvenile steelhead were affected most, but probably did not suffer substantial mortality because of their rapid movement to the ocean.  Salmonid tolerance to supersaturation and their ability to detect and avoid supersaturation seem dependent on life stage, species, stock, and environment.

Lethal conditions may prevail in certain areas at certain times, so knowledge of the tolerance limits for resident and migrant fishes impacted by supersaturation is essential to assess the necessity for counteractive measures.  Future studies at The Dalles Dam during a period of high supersaturation are necessary to satisfy the objectives of this study.