Table 15. --Estimated numbers of age and age 

 I sockeye salmon migrating from Coville Lake 

 to Grosvenor Lake (by 10-day periods) , July 11 

 to September 7, 1964, based on results of 

 fishing with 4-ft fyke nets in Coville River. 



originated in Grosvenor Lake or had spent at least one 

 winter there because age I fish were virtually absent 

 from the Coville River summer migrations. 



My estimate of the number of age sockeye salmon 

 that migrated from Grosvenor Lake to Iliuk Arm from 

 15 July to 17 September 1962 is 3.9 million (Table 16). 

 This estimate is made by expanding the daily estimates 

 by a factor of 20. The factor of 20, though subjective, 

 is believed to be conservative and was selected after 

 considering the width of the channel at the fishing site 

 (about 76 m), other physical conditions (such as water 

 depth and current velocity), and the behavior of these 

 migrating fish in relation to the fyke nets at Grosvenor 

 and Coville Rivers. 



Significance of the Summer 

 Outmigrations from Coville Lake 



The significance of the summer outmigrations of age 

 sockeye salmon from Coville Lake can now be con- 

 sidered. The best estimates of the number of age 

 sockeye salmon in Coville Lake about 1 September 

 and estimates of the number that migrated from the 

 lake during the summer each year from 1961 to 1964 

 are shown in Table 17. The number that migrated in 



Table 16. --Estimated numbers of age sockeye 

 salmon migrating from Grosvenor Lake to Iliuk 

 Arm (by 10-day periods) , July 15 to September 

 17, 1962, based on fyke net catches in Grosve- 

 nor River. 



Period 



Age fish 



July 15-21 

 July 22-31 

 August 1-10 

 August 11-20 

 August 21-30 

 August 31-September 9 

 September 10-17 

 Total 



860 



67,400 



126,180 



842,960 



941,280 



499,500 



1,590,940 



3,870,900 



1961, 1962, and 1964 greatly exceeded the number that 

 remained in the lake and in 1963, the number that mi- 

 grated was equal to the number that remained in the 

 lake. Furthermore, in none of the years did the migra- 

 tion appear to be over when the sampling was ended. 

 Although none of these data are precise, the summer 

 outmigration of age fish from Coville Lake appears 

 to be significant to that lake. 



The question of whether significant numbers of age 

 sockeye salmon remain in Coville Lake through the 

 winter to migrate as age I smolts cannot be answered 

 directly. Because ice frequently persists in Coville and 

 Grosvenor Lakes until early June, it is difficult to 

 reach Coville River and sample the spring migration. 

 In 1961 and 1962 the migration apparently started 

 while ice covered the lakes and was well underway 

 when sampling began because the rate of migration of 

 age I fish (assumed to be smolts) generally declined 

 from the first sampling. It is possible that the migration 

 of age fish usually continues into the fall and only 

 relatively few fish remain to migrate as age I. Ruggles 

 (1966) reported such an overwinter shift in distribution 

 (seaward) of presmolts between basins of Owikeno 

 Lake, British Columbia. 



Table 17. --Number of age sockeye salmon in 

 Coville Lake at the end of summer (September 

 1) and number that migrated from the lake dur- 

 ing the summer, 1961-64. 



Product of average catch per standard 

 tow and number of standard tow volumes to a 

 depth of 10 m; there are about 61,000 such 

 standard tow volumes in Coville Lake, 



Evidence on the immediate fate of age sockeye 

 salmon that leave Coville Lake indicates that these 

 fish continue downsystem through Grosvenor Lake 

 and into Iliuk Arm the same summer. This evidence, 

 which is circumstantial and pertains to numbers and 

 size of the fish, comes from fyke netting in Coville and 

 Grosvenor Rivers and tow netting in Grosvenor Lake 

 and Iliuk Arm. The data indicate that age sockeye 

 salmon migrating from Coville Lake during the sum- 

 mer continue downsystem into Iliuk Arm within a few 

 weeks. 



The immediate fate of age sockeye salmon that 

 migrated from Coville Lake to Grosvenor Lake can be 

 inferred from the number that enter and the number 



