FISHERY BULLETIN: VOL 77, NO. 1 



travel time and in size and age of migi'ants. No 

 estimates of mortality of any given gi-oup of sock- 

 eye salmon could be made from their data or from 

 other studies conducted at the various dam proj- 

 ects. However, we have assumed that extremely 

 large losses occur in each annual outmigration of 

 sockeye salmon, comparable to those documented 

 for Chinook salmon and steelhead trout. 



Losses can occur in but a short distance during 

 the seaward journey. Ellis and Noble (1960) re- 

 ported losses of fall chinook salmon of 12.2 to 

 29.7% in the Klickitat River in a distance of only 

 64 km. The Wenatchee stock sockeye salmon 

 smolts had to navigate 844 km in their seaward 

 migration and were subjected to injuries and pos- 

 sible death at each of seven dams, plus the myriad 

 effects of altered flows and water quality. 



Major direct causes of mortality in juvenile mi- 

 grants are gas bubble disease, a result of high 

 dissolved nitrogen concentrations which occur 

 throughout the river and death or injury by pass- 

 ing through turbines (Ebel et al. 1973). At high 

 flows with excessive spill the fingerlings are sub- 

 jected to the nitrogen problem, while the turbine 

 caused losses are most severe at low flows. Chaney 

 and Perry ( 1976) reported that the juvenile losses 

 averaged 15 to 20% at each mainstem dam from 

 combined causes. At low flows, cumulative fish 

 losses just from turbine mortality at a series of 

 seven dams may exceed 90'/f . 



Additional mortality can be expected from sev- 

 eral other causes. The delay of stream flow in the 

 impoundments has reduced migration rates of 

 juveniles by one-third according to Raymond 

 (1969). The fish are then subject to increased pre- 

 dation, possible loss of marine adaptability, and 

 may become residual in the reservoir. Undoubt- 

 edly but a small part of the outmigrants ever reach 

 the sea in some years. 



Adult Problems 



We surmise that the sockeye salmon suffer loss- 

 es comparable to the other species in the ocean, but 

 there is no appreciable fishery harvest. The few 

 tagging returns that have been reported for Co- 

 lumbia sockeye salmon (Margolis etal. 1966) indi- 

 cate a more southerly distribution than for Cana- 

 dian or Washington sockeye salmon, and there is 

 no inshore marine fishery to intercept the adults. 



The relatively few remaining adult sockeye 

 salmon, after surviving the perils of sea life, still 

 must face serious obstacles on the spawning mi- 



gration. Aside from the commercial harvest, a 

 substantial mortality occurs which cannot be 

 measured precisely. In early reports of upriver fish 

 passage, Schoning (1948) pointed out that annu- 

 ally an average of 36% of the Bonneville Dam 

 count could not be located after subtracting the 

 known harvest. "Fall-back" contributes to the loss 

 and obscures the actual number passing the dam. 

 Later accounts corroborate these losses (Chaney 

 and Perry 1976). Bonneville Dam mortalities 

 would reduce the number offish available for har- 

 vest only in the zone 6 portion of the fishery. 



SUMMARY 



1. The Columbia River system produced large 

 runs of sockeye salmon prior to 1900, providing an 

 annual commercial harvest reaching 2 million kg. 



2. Deterioration of spawning areas and blockage 

 of tributaries caused a severe decline in the sock- 

 eye salmon population early in this century. 



3. Construction of Grand Coulee Dam in 1941 

 blocked the sockeye salmon from 1,835 km of 

 spawning and rearing areas, virtually eliminat- 

 ing all natural production. 



4. Compensatory measures intended to replace 

 the lost production included relocation of the sock- 

 eye salmon runs to suitable areas below Grand 

 Coulee Dam and construction of hatcheries for 

 additional production. 



5. Leavenworth National Fish Hatchery on the 

 Wenatchee River was activated in 1940 as the 

 primary fish production station and an annual 

 stocking program of sockeye salmon fingerlings 

 was started. 



6. For over 20 yr Leavenworth Hatchery reared 

 sockeye salmon, releasing the fingerlings into the 

 Wenatchee system augmenting the natural pro- 

 duction. 



7. No assessment had been made of the actual 

 contribution of hatchery fish to the commercial 

 fishery, thus the subject study was initiated using 

 the 1960-63 broods of sockeye salmon. 



8. During the initial 4 yr of the study, a total of 

 11,538,291 fish were released, of which 3,390,941 

 were marked by removal of the adipose fin and a 

 part of the maxillary bone. 



9. The stock used was adult .sockeye trapped in 

 tributaries of Lake Wenatchee. Fingerlings were 

 reared at the hatchery until fall, then released 

 into Lake Wenatchee. 



10. Surviving smolts migrated out of the lake in 

 the spring. Outmigrant trapping in the first 2 yr 



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