Abstract. A flow and survival re- 

 lationship, based on 1970's research, for 

 juvenile chinook salmon, Oncorhynchus 

 tshawytscha, that migrate through the 

 Snake and Columbia Rivers is the foun- 

 dation of many fishery managers' rec- 

 ommendations for modifications to the 

 hydropower system to stem the decline 

 of populations recently listed under the 

 Endangered Species Act. However, a 

 review of the 1970's data found that 

 estimated fish survivals through the 

 hydropower system reflected conditions 

 that no longer exist and that between 

 1977 and 1979 these estimated surviv- 

 als were negatively biased. Debris en- 

 trained in front of, and throughout, the 

 fish collection system of the uppermost 

 dam on the Snake River resulted in fish 

 descaling and most likely poor fish sur- 

 vival. Under the lowest flow conditions, 

 decreased survival due to increased 

 travel time was exacerbated by spo- 

 radic or less than optimal turbine op- 

 erations, or both, which further delayed 

 fish passage through the dams and, at 

 the uppermost dam, subjected fish to 

 debris for longer periods of time. Use 

 of flow and survival relationships based 

 on yearly estimates of juvenile migrant 

 survival in the 1970's will probably not 

 accurately predict survival of spring- 

 migrating juvenile chinook salmon un- 

 der present conditions. This is particu- 

 larly true for survival predictions dur- 

 ing low-flow conditions. 



A review of flow and survival 

 relationships for spring and 

 summer chinook salmon, 

 Oncorhynchus tshawytscha, 

 from the Snake River Basin 



John G. Williams 

 Gene M. Matthews 



Coastal Zone and Estuarine Studies Division, Northwest Fisheries Science Center 



National Marine Fisheries Service, NOAA 



2725 Montlake Boulevard East, Seattle, Washington 981 12-2097 



Manuscript accepted 17 April 1995. 

 Fishery Bulletin 93:732-740 ( 1995). 



The Columbia River watershed his- 

 torically has produced more chinook 

 salmon, Oncorhynchus tshawytscha, 

 than any other river system in the 

 world (Netboy, 1980). The majority 

 of the spring chinook salmon origi- 

 nated in the Snake River Basin 

 (Fulton, 1968). In the early 1880's, 

 spring and summer chinook salmon 

 provided commercial fisheries in the 

 lower Columbia River with average 

 annual catches of 17.7 million kilo- 

 grams (Craig and Hacker, 1940). 

 Heavy exploitation by these fisher- 

 ies, however, caused a substantial 

 depletion of the dominant summer 

 stock; the fisheries, therefore, con- 

 centrated on the spring and fall 

 stocks (Craig and Hacker, 1940; 

 Gangmark, 1957). Summer chinook 

 salmon populations from the mid- 

 and upper Columbia River contin- 

 ued to decline such that by 1964 the 

 commercial fishery for all summer 

 fish was closed. By this time, Snake 

 River Basin spring and summer 

 chinook salmon accounted for ap- 

 proximately 78 percent of the re- 

 maining upper river populations 

 (Fulton, 1968). 



The primary causes of stock de- 

 clines in the early years were over- 

 fishing, habitat destruction, and 

 damming of tributaries for water 

 withdrawal and small-scale hydro- 

 power (Craig and Hacker, 1940). 



Concern about the potential im- 

 pacts on upstream salmonid migra- 

 tion and the loss of downstream 

 migrant juveniles passing through 

 turbines at mainstem hydropower 

 projects was expressed even before 

 construction of Bonneville Dam 

 (Fig. 1)( Griffin, 1935). Because the 

 river flow during the time of the 

 juvenile migration generally far 

 exceeded the capacity of the power- 

 house turbines, most fisheries re- 

 search related to migrant salmonid 

 passage was directed toward adults 

 and the development of adequate 

 upstream passage facilities for them 

 at dams. However, some research on 

 juvenile salmonid survival through 

 turbines was conducted in the early 

 1940's 1 after construction of Bonne- 

 ville Dam and in 1954 after con- 

 struction of McNary Dam (Schoene- 

 man et al., 1961). 



The first comprehensive program 

 to study of juvenile salmonid mi- 

 grants in the mainstem Columbia 

 and Snake Rivers was initiated in 

 1961 by the Secretary of the U.S. 

 Department of Interior. The pro- 

 gram was instigated by construc- 

 tion of the high-head Brownlee Dam 



1 Holmes, H. B. 1952. Loss of salmon fin- 

 gerlings in passing Bonneville Dam as de- 

 termined by marking experiments. U.S. 

 Fish Wildl. Serv. Unpubl. manuscr., 62 p. 



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