facility, it is possible there could have been sig- 

 nificant delayed effects. The effect of pumping on 

 juvenile chinook salmon and steelhead 

 trout— when added to other cumulative stresses 

 associated with handling in our transport process 

 —is indicated by the lower percentage of adult 

 returns from control releases of juveniles in 1970. 



Although smaller numbers of juvenile chinook 

 were released in 1969-70 than in 1968 and a 

 correspondingly small number of adults returned, 

 we believe that the lower percentage of returning 

 adults does indicate that stress factors due to 

 handling were higher in 1970 than in 1969. The 

 addition of two dams-Lower Monumental and 

 Little Goose-placed in operation in 1969 and 1970, 

 upstream from Ice Harbor Dam, must also be 

 considered. Fish had to pass through Lower 

 Monumental Reservoir and Dam in 1969 before 

 being collected at Ice Harbor Dam. In 1970, they 

 had to pass through both reservoirs and dams 

 before being collected. Supersaturation of dis- 

 solved nitrogen also became a problem between 

 Little Goose and Ice Harbor dams at this time. 

 Turbines from both Lower Monumental and Little 

 Goose dams were not scheduled for installation 

 until after the spring freshet and as a result large 

 volumes of water had to be passed over the spill- 

 ways, causing dissolved gas concentrations to be 

 high; a large percentage of the fish arriving at Ice 

 Harbor Dam e.xhibited obvious signs of gas bubble 

 disease. 



If we use the percentage adult returns in rela- 

 tion to juveniles released at the Rapid River 

 Hatchery in Idaho as an indicator of the rate of 

 return of naturally migrating chinook salmon and 

 we compare our percentage return figures, we 

 find our estimate of return of controls was 4.3%' in 

 1968-much higher than the 0.48% adult return 

 recorded for Rapid River Hatchery.' The estimat- 

 ed control return of 0.497% for the 1969 outmigra- 

 tion is comparable to the 0.493% return to Rapid 

 River Hatchery, but estimated returns from con- 

 trols released in 1970 dropped to 0.323% whereas 

 the return to the Rapid River Hatchery was 

 0.477%. Thus, the stresses placed on juvenile fish 

 prior to collection, in addition to those involved in 

 the handling process, conceivably were in- 

 strumental in causing the lower return of adults 

 from the 1969-70 e.xperiments. 



When we examine adult returns from juvenile 



control releases of steelhead trout, we find that the 

 percentage return from control releases of 

 steelhead trout in 1969-70 were much greater than 

 for comparable juvenile releases of chinook salm- 

 on. This indicates that the ability of steelhead 

 trout to withstand the cumulative effects of stress 

 is greater than that of chinook salmon. 



Using the adult return percentage of steelhead 

 trout to the Dworshak Hatchery from juvenile 

 migrants released at that site in 1970 as a base 

 indicator of the adult return of naturally migrat- 

 ing steelhead trout to Idaho streams, we find that 

 our estimated adult returns from control releases 

 to Ice Harbor and Little Goose dams of 0.792 and 

 0.729% (in 1969 and 1970, respectively) were 

 somewhat greater than the 0.682%' return to 

 Dworshak Hatchery. When our adult control re- 

 turns are adjusted for the upriver sport catch on 

 steelhead trout, our revised return (0.713% from 

 the juvenile control releases in 1969) was com- 

 parable to the 0.682% return to Dworshak 

 Hatchery. The return from the 1970 (control) 

 release of 0.598% was, however, less than the 

 hatchery return of 0.682%. 



Based on the foregoing rationale, we believe 

 that our control releases of juvenile chinook salm- 

 on and steelhead trout in 1969 returned as adults 

 at rates comparable to those of natural migrat- 

 ing salmonids and that benefits on survival to 

 adults indicated for our transported salmon and 

 steelhead trout represent real increases. 



Studies to further define stress problems as- 

 sociated with diversion, collection, and handling of 

 naturally migrating juveniles are currently un- 

 derway. To maximize the effectiveness of a 

 collection and transportation system, stresses 

 from all sources must be minimized. 



Conclusion 



The homing of adult fish, captured during their 

 seaward migration as juveniles and transported 

 downstream (from Ice Harbor Dam to Bonneville 

 Dam), was not reduced by the transport operation. 

 Although numbers of returning adults were small, 

 comparisons of returns of transported fish versus 

 control fish to Ice Harbor Dam, the spawning 

 grounds, and hatcheries in Idaho indicated that 

 they "homed" satisfactorily. No evidence of 

 straying of transported fish was observed in our 

 surveys. 



Ters. commun. Evan Parrish, Hatchery Manager, Rapid River 

 Hatchery, Riggins, Idaho. 



'Pers. commun. Einer Wold, Hatchery Pathologist, Dworshak 

 Hatchery, Ahsahka, Idaho. 



930 



