Williams and Matthews: Flow and survival relationships for Oncorhynchus tshawytscha 



737 



ite Dam were partially cleared of debris with the steel 

 beam. 4 



Fish passage conditions were particularly bad at 

 Little Goose Dam in 1973 and Lower Granite Dam 

 in 1977 because river flows were so low that little 

 (1973) to no (1977) spill occurred at Snake River 

 dams. Thus, nearly all fish had to pass through 

 trashracks at dams into either the turbines or the 

 debris-laden bypass systems. Additionally, it was not 

 unusual for one or more turbines to operate at full or 

 nearly full capacity for relatively short periods dur- 

 ing the evening peak load and then shut down for 

 relatively long periods (authors' personal observa- 

 tions). At other times, one or two turbines were op- 

 erated at partial capacity for relatively long periods. 

 The slowing or stopping of turbines probably delayed 

 dam passage by reducing or stopping the flow into 



each turbine and, thus, fish were not 

 attracted to the bypass. 



Under these conditions in 1977, 10— 

 14% of spring and summer chinook 

 salmon smolts within 140 m of the fore- 

 bay at Lower Granite Dam were descaled 

 (a fish was considered descaled if it was 

 missing 10-100% of its scales), whereas 

 fish sampled 400 m to 2 km upstream 

 showed no descaling. 5 These observa- 

 tions suggest that fish were delayed at 

 the dam and that they swam in and out 

 of the debris-covered trashracks, possi- 

 bly while loads were adjusted or when 

 velocities were insufficient to draw fin- 

 gerlings completely into the bypasses 

 or through the turbines. For fish that 

 passed into the collection facility, an 

 average of 26.0% were descaled. Under 

 similar conditions at Little Goose Dam, 

 the percentage offish descaled averaged 

 19.6 and 23.0% in 1973 and 1977, re- 

 spectively, probably because they hit 

 something during passage through the 

 trashracks or bypass system. (The high 

 level of descaling observed in 1977 most 

 likely resulted from the fact that fish 

 had previously passed Lower Granite 

 Dam.) When debris partially occluded 

 openings through which fish passed, it 

 not only provided objects that the fish 

 hit but caused increased water velocity 

 through the remaining open area. Thus, fish hit the 

 debris with more force as the amount of debris in- 

 creased. A fish with external injury, such as descaling, 

 would likely have had internal injury as well. To de- 

 termine the relationship between descaling percent- 

 age (as a measure of total injury) and mortality 

 within a short time period, random samples of by- 

 pass fish were collected during some years and held 

 in tanks with flow-through river water. The rate of 

 mortality during approximately 48 hours of holding 

 was measured, and the extent to which this was de- 

 pendent upon descaling percentage was evaluated. 

 Facility-caused descaling was highly positively cor- 

 related with delayed mortality for marked untrans- 

 ported fish (#=0.94, P<0.002) and unmarked trans- 

 ported fish (#=0.90, P<0.007), whereas it was fairly 



4 Smith, J. R., G. M. Matthews, L. R. Basham, S. Achord, and G. 

 T. McCabe. 1980. Transportation operations on the Snake 

 and Columbia Rivers, 1979. Report to U. S. Army Corps of 

 Engineering, Walla Walla, WA, 28 p. Northwest Fish. Sci. 

 Cent., NMFS. 



5 Park, D. L., J. R. Smith, E. Slatick, G. M. Matthews, 

 L. R. Basham, and G. A. Swan. 1978. Evaluation offish pro- 

 tective facilities at Little Goose and Lower Granite Dams and a 

 review of mass transportation activities, 1977. Report to U.S. 

 Army Corps of Engineering, Portland, OR, 60 p. Northwest 

 Fish. Sci. Cent., NMFS. 



