- 3001 



m 



a 



z 



4 

 (/) 



3 

 O 



X 



200- 



X 



in 



O 100 



o 



Z 



-^F-^t 



th^ 



25 50 75 100 125 150 175 200 

 FORK LENGTH (MM.) 



Figure 11. — Length-frequency distribution of 1,626 

 juvenile hatchery-reared sockeye salmon from the 

 Snake River collected below Brownlee Dam, March 21 

 to May 13, 1965. 



Emigration was notably more successful in 1964 

 and 1965 when the reservoir level was low through 

 most of the downstream migration, and discharges 

 were high during early and midspring. 



Fish that entered the reservoir after the middle 

 of June, as kokanee did in 1964 and 1965 (fig. 5), 

 had poor success of passage. In both years, emi- 

 gration of kokanee was less successful than that 

 of other species of fish migrating earlier in the 

 season. Kokanee did not enter the reservoir until 

 late June when the reservoir was fuU and currents 

 were weak and not clearly oriented in any direc- 

 tion. Those fish remaining in the reservoir through 

 the summer encountered low oxygen concentra- 

 tions (0-3 p.p.m.) below the thermocline and high 

 water temperatures (24° C. or above) near the 

 surface (Ebel and Koski, 1968). Few kokanee sur- 

 vived the harsh summer. 



MORTALITY RELATED TO TURBINES 



Because.many fish were found dead in the scoop 

 traps, the mortality attributable to the traps and 

 the turbines was examined. A detailed investiga- 

 tion was beyond the scope of this study, but 

 mortality was assessed at the turbine tailrace site 

 in June 1965. During a 6-day period (June 1-6), 

 all scoop traps were emptied twice daily — at 8:00 

 a.m. and 4:00 p.m. In a second 6-day period 

 (June 7-12), all fish were removed as soon as they 

 entered the traps (table 15). All fish caught during 

 both periods were hatchery-reared chinook salmon 

 of the 1965 year class. 



258 



Mortality during the two periods was as indi- 

 cated in table 15: 88 percent of the fish were 

 dead in the traps in the first period, and 16 per- 

 cent were dead when they entered the traps in 

 the second period. Because the fish were removed 

 immediately in the second period, they died of 

 causes other than trapping or handling. 



To assess delayed mortality, samples of live 

 fish taken from the traps during the second period 

 were held in a holding tank in circulated water for 

 an additional 24-hour period. Hatchery-reared 

 chinook fingerlings collected in the reservoir 

 above the dam were held with these fish to serve 

 as a control (table 16). At the end of 24 hours, 

 67.5 percent of the fish taken from the traps and 

 17.5 percent of the control fish were dead. Thus, 

 the delayed mortality of fish passing through the 

 turbines was 50 percent. 



Thus, on the average under test conditions, 16 

 of every 100 fish passing the sampling site were 

 already dead. Of the 84 survivors, 42 died within 

 24 hours, which indicated a total turbine-related 

 mortality of 58 percent. 



Table 15. — Mortality of juvenile hatchery-reared chinook 

 salmon taken by scoop traps at the turbine tailrace sampling 

 site, June I-IS, 1966 



Turbine Water Fish In 

 Date discharge temper- total catch Mortality 



ture 



MMuc. °C. Number Number Percent 



Period A;' .„ ,., „ «, 



Junel 481 " ^25 SS m 



June 2 484 13 8^ 77 M 



JmeS 478 18 167 160 96 



June4 470 18 230 216 94 



Junes ... 472 14 160 146 91 



juHe o::::::: 410 18 323 274 ss 



Totals 1,068 939 88 



^f^,l' 847 18 148 26 18 



juS68::..:.:.:... 823 w es 12 » 



June9 440 18 23 1 4 



June 10 - 433 16 18 1 6 



Junen 423 16 4 J ?S 



June 12 334 17 16 2 13 



Totals 273 43 16 



1 Normal operathig conditions. Trap emptied at %-S» a.m. and 4:00 p.m. 

 dally. 

 » Fish removed from trap Immediately upon entry. 



Table 16. — Delayed mortality of juvenile hatchery-reared 

 chinook salmon taken from the tailrace scoop traps, 

 June 7-12, 1966 



Group 



Fish In Mortality at the 

 trap end of 24 hours 



Number 



ExperimentaL ,^ 



Control »•» 



Number Percent 

 66 67.8 



18 17.8 



U.S. FISH AND WILDLIFE SBBVICE 



