Williams and Matthews: Flow and survival relationships for Oncorhynchus tshawytscha 



735 



40 50 60 70 80 90 100 110 120 130 140 150 160 170 



Flow (kefs) 



Figure 2 



Survival estimates for juvenile spring and summer chinook salmon, 

 Oncorhynchus tshawytscha, migrating through the upper dam (Little Goose 

 Dam, 1973-74; Lower Granite Dam, 1975-79) on the lower Snake River to 

 either John Day Dam (1976-79) or The Dalles Dam (1973-75) compared 

 with the average river flow at Ice Harbor Dam during the period (±7 days ) 

 of peak migration for the years 1973 through 1979 (data from Sims and 

 Ossiander [1981][see Footnote 3]). 



system (1973 and 1977) were mainly a 

 result of low survival in the Snake 

 River. Although the low flows increased 

 travel time, more significantly, the en- 

 tire migrant fish population was sub- 

 jected to debris problems at the upper- 

 most Snake River dam. Additionally, as 

 a result of low flows, turbine operations 

 were cut dramatically during nighttime 

 hours (when fish normally pass dams) 

 so that fish were delayed further and 

 thus subjected to the effects of the de- 

 bris for longer periods. We then com- 

 pared the low 1970s survival estimates 

 with some Snake River survival esti- 

 mates of recent years. 



Data review 



Effects of dam operations and 

 debris on fish condition 



to Bonneville Dam under present river conditions. 

 To calibrate the models, they were fitted to the 1970s 

 NMFS flow and survival data (after altering them to 

 represent the turbine, bypass, and spill conditions 

 that existed in the 1970's). 



However, present river conditions and dam opera- 

 tions differ substantially compared with those in the 

 1970's. Further, detections in recent years of marked 

 fish that migrated through the Snake River to 

 McNary Dam under relatively low flows indicate that 

 juvenile fish survive at a rate substantially higher 

 than that which would be predicted from flow and 

 survival relationships derived from the 1970's data. 

 Because recent information is not in agreement with 

 past data, but because the 1970's data are the foun- 

 dation of some of the present computer models, we 

 initiated a critical review of the NMFS data from 

 the 1970's to determine whether these data were still 

 relevant. 



We initially reviewed all the NMFS data files from 

 which estimates of survival were reported. These 

 included original NMFS field notes, analyses of mark 

 and recapture data, and yearly research summaries. 

 We also reviewed field notes and data summaries 

 from other concurrent NMFS research that docu- 

 mented the condition of fish collected at dams. On 

 reviewing the original data, we determined that the 

 lowest estimates of survival within the hydropower 



Juvenile salmon mortality for Snake 

 River migrants was initially somewhat 

 minimized because when the dams were 

 first built, they were equipped with only 

 three operating turbine units. This limited the 

 amount of flow through the powerhouses to approxi- 

 mately 1,840-1,980 nv^s" 1 (65-70 thousand cubic feet 

 per second [kefs]). From 35 to 75% of the total river 

 flow (and a presumed equal percentage of the fish 

 population) passed over the spillways during the 

 spring seaward migration. Except under conditions 

 where high atmospheric gas supersaturation de- 

 creased survival ( Ebel and Raymond, 1976), survival 

 of juvenile migrant fish through spillways was gen- 

 erally estimated at greater than 97% (Raymond, 

 1988). Three additional turbines were added to Ice 

 Harbor Dam in 1975, to Little Goose and Lower Gran- 

 ite Dams in 1978, and to Lower Monumental Dam 

 in 1979. This led to progressively less uncontrolled 

 spill in the Snake River and a concomitant increase 

 in fish passing through turbine intakes. To decrease 

 fish mortality in the turbines, many of the fish that 

 passed into turbine intakes at Little Goose and Lower 

 Granite Dams were diverted to bypass and collec- 

 tion facilities (Smith and Farr, 1975; Matthews et 

 al., 1977). However, the potential benefit of these 

 bypass systems in decreasing the mortality of fish 

 entering turbine intakes was compromised prima- 

 rily because of debris that had collected at the dams. 

 With the exception of Ice Harbor Dam (which had 

 a debris boom installed), huge amounts of woody de- 

 bris began to accumulate at the upstream face, in 



