WAHLE ET AL., 1960-63 BROOD HATCHERY-REARED SOCKEYE SALMON 



retention phase of the project. Cumulative long- 

 term effects on outmigrants may have been sub- 

 stantial. Other viral diseases, about which little 

 was known at the time, may have been present. 



Lake Existence 



A high rate of mortality occurred in Lake 

 Wenatchee during the period of lake rearing, and 

 this was probably spread over the period from 

 stocking until outmigi'ation. Losses similar to the 

 62 and 51%, found where outmigrants were enum- 

 erated, undoubtedly occurred in the 2 yr in which 

 outmigrants were not counted. Foerster ( 19681 re- 

 ported that the average smolt migration from 

 British Columbia and Alaska lakes where only fry 

 were stocked was 44% and the survival to return 

 ranged from 11 to 84% . The hatchery rearing at 

 Leavenworth seemed an economic waste, as equal 

 outmigration rates may have been obtained using 

 fry plants. 



There is an extensive sport fishery in Lake 

 Wenatchee on Dolly Varden, Sa!ve!iiu/s malma, 

 and kokanee, a nonmigrant strain of sockeye 

 salmon. We monitored this fishery in order to de- 

 termine the effect on released study fish. 



Incidental to the trout catch, a fairly large 

 number of sublegal ( <6-in) hatchery salmon were 

 taken. This was determined by the presence of 

 marked fish in a sample of sublegal fish in the 

 angler catch. The hatchery fish were caught dur- 

 ing the early spring of their second year just prior 

 to their outmigration. Most sublegals were re- 

 leased by the anglers, but mortality undoubtedly 

 resulted from hooking and handling. Addition- 

 ally, some of the marked sockeye salmon remained 

 in the lake without migrating and were observed 

 throughout the season in the creel checks of legal- 

 sized trout. The percentage becoming resident was 

 unknown, but in 1964 represented 1.4% of the 

 calculated total kokanee sport catch of 17, 523 fish. 



Sockeye salmon becoming resident in the lake 

 and entering the sport fishery, based on 1964 data, 

 accounted for <1% of the stocked fish. The mortal- 

 ity of sublegal fingerlings from angling was as- 

 sumed to be small because of their rare occurrence 

 in the sport catch. Health records of the hatchery 

 fish did not indicate any expected loss from disease 

 or parasites. Undoubtedly, the large loss of finger- 

 lings was due to predation by larger fish and possi- 

 bly starvation. 



The heaviest loss of fingerlings in the lake was 

 certainly caused by predation. Although precau- 



tions were taken during release, when fish were 

 barged to avoid shoreline concentrations. 

 Thompson and Tufts (1967) reported heavy preda- 

 tion both during and following release periods. 

 Dolly Varden and northern squawfish, 

 Ptychocheilus oregonensis, were sampled by gill 

 net and trolling gear. Dui-ing the weeks of release, 

 the number of captured fish containing sockeye 

 salmon ranged from 58 to 100% . Gangmark and 

 Fulton (1952) during experiments in 1949-51 re- 

 ported heavy predation by the same species. Our 

 own observations of angler-caught fish from 

 March through July 1962 showed an average of 

 over one sockeye salmon per stomach. No estimate 

 of the total predation loss was possible as the total 

 number of predators was not known. 



From our observations and those reported by 

 Allen and Meekin (1973) the zooplankton produc- 

 tion in the lake peaked in August and September 

 each year. The hatchery fish, stocked in October, 

 were faced with a declining food supply. Growth 

 apparently stopped during the winter. Fingerlings 

 of the 1961-brood averaged 97 mm FL when 

 stocked in October whereas in the following 

 spring, migrants trapped at the outlet, had a size 

 range of 87-98 mm FL (Weber and Wahle 1969). 

 Low food productivity of the lake, coupled with 

 competition from natural resident fish for food, 

 undoubtedly affected the fitness of the migrant 

 sockeye salmon and possibly caused subsequent 

 losses from stress on the seaward journey. 



It is highly improbable that any hatchery pro- 

 duction program utilizing an additional rearing 

 period in Lake Wenatchee could succeed. How- 

 ever, even if no loss had occurred during lake resi- 

 dence, thus doubling the number of hatchery out- 

 migrants, no more than a twofold increase in 

 adults could be expected. Even with such an im- 

 provement, still more than 10 times that number 

 of adults would be required for a favorable 

 benefit/cost ratio. 



Downstream Migrant Problems 



With a large portion of the production sacrificed 

 in the lake, the remaining smolts were still faced 

 with gi-eat problems. Until recently, little was 

 known of the causes and extent of downstream 

 losses of sockeye salmon, although much informa- 

 tion has been obtained for chinook salmon and 

 steelhead trout smolts. Anas and Gauley 11956) 

 studied the seaward migration of sockeye salmon 

 smolts and their data suggested a wide range in 



239 



