FIG. 6 Length frequency of squawfish taken in Merwin trap at 

 Lyons Ferry in June, 1974. 



TABLE 4 Purse Seine Results From Catches in the Tailrace 

 of Little Goose Dam, 1974 



to normal, catches increased to 1,935 in 5 days of 

 seining with an increase to 161.2 fish per set. All 

 fish checked in the latter sample showed evidence 

 of feeding heavily on lamprey ammocetes 

 Entosphenus tridentatus, (Gairdner). 



We might interpret the presence or absence of 

 squawfish in the tailrace at Little Goose Dam as 

 being influenced by high dissolved gases. Satura- 

 tion in the spill and adjacent areas around the dam 

 tended to keep squawfish away; and after gas satu- 



ration returned to normal they moved in to feed on 

 whatever was available, which was mainly lamprey 

 ammocetes. On the other hand, it is possible that 

 large numbers of squawfish may have been present, 

 but below the depth of our net where they would 

 also be at sufficient depth to compensate for gas 

 supersaturation and thus be safe from the disease. 

 We do not know if they are at this depth. Thus, what 

 appeared to be a response to high nitrogen levels 

 could be the result of normal behavior patterns in 

 the vicinity of spill gates and turbine discharge 

 draft tubes at dams. It is evident, however, that 

 those squawfish taken during high dissolved gas 

 saturation were not effective predators. 



CONCLUSION 



Laboratory studies indicated that adult squaw- 

 fish are susceptible to supersaturation of atmospheric 

 gas at or exceeding 117% and exposure to these 

 levels significantly reduced their food intake. 



Field studies indicated that exposure of squaw- 

 fish to supersaturation could be an important factor 

 in assessing the effects of predation on juvenile 

 salmonid migrants in the Columbia River but more 

 information is needed on their movement, behavior 

 and depth distribution before an accurate assess- 

 ment can be made. 



REFERENCES 



Beiningen, K. T., and W. J. Ebel. 1970. Effect of John Day 

 Dam on dissolved nitrogen concentrations and salmon in the 

 Columbia River, 1968. Trans. Am. Fish. Soc. 99.664-671. 



Blahm, T. 1974. Squawfish Bioassay. Bonneville Power Ad- 

 ministration Quarterly Report, National Marine Fisheries 

 Service, Prescott Field Station, unprocessed. 



Brett, J. R. and J. A. McConnell. 1950. Lakelse Lake sockeye 

 survival, your. Fish. Res. Bd., Can. 8(2j:83-110. 



Dawley, E. M. and W. J. Ebel. 1973. Lethal and Sublethal 

 Effects of Various Levels of Nitrogen and Argon Supersatura- 

 tion on juvenile Chinook Salmon and Steelhead Trout. National 

 Marine Fisheries Service Bulletin. In press. 



Dawley, E. M., M. Schiewe, B. Monk and F. Ossiander. 1975. 

 Effect of Long-term Exposure to Supersaturation of Dissolved 

 Atmospheric Cases on juvenile Chinook Salmon and Steelhead 

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Ebel, W. J. 1969. Supersaturation of nitrogen in the Columbia 

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 68:1-11. 



Hamilton, ). A. R., L. O. Rothfus, N. W. Erho, and J. D. Remington. 

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 Bull. No. 9, 65 pp. 



Meekin, T. K. and B. K. Turner. 1974. Tolerance of Salmonid 

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 Wash. Dept. Fish., Tech. Rpt. No. 12, pp. 78-126 (9 figures, 

 15 tables, 9 references). 



Mighell. ). L. 1969. Rapid cold-branding of salmon and trout 

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Thompson, R. B. 1959. Food fo the squawfish, Ptychocheilus 

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46 Bentley, Dawley, Newcomb 



