Coville Lake (Table 11) involve both time and depth, 

 which may reflect the offshore movement of adults 

 after the early summer spawning and recruitment of 

 yearlings to catchable size. The seasonal change in 

 abundance was not as evident in West End, where this 

 species occurred in greatest numbers. No consistent 

 year-to-year trends in abundance were observed. 



The abundance of ninespine sticklebacks in tow net 

 catches exceeded that of threespine sticklebacks only 

 in area C-l of Coville Lake — this is the uplake end 

 adjacent to large areas of submerged aquatic plants, 

 mostly Potamogeton spp. The catches of the two 

 species were about equal in the rest of Coville Lake, 

 but in the other lakes ninespine sticklebacks were gen- 

 erally much less abundant than threespine stickle- 

 backs. 



INTERLAKE MIGRATION OF 

 PRESMOLT SOCKEYE SALMON 



Although juvenile sockeye salmon normally trans- 

 form to smolts and migrate to salt water at age I or 

 older, some oceanward migration of presmolts (age 

 fish) has been reported 7 (Narver, 1968). Outmigrations 

 of presmolt sockeye salmon amounting to as much as 

 21% of the subsequent smolt production for the brood 

 year had occurred in Brooks River in 1958 and 1960 

 and again in 1961. In the summer of 1961 a similar 

 migration of age fish from Coville Lake to Gros- 

 venor Lake via Coville River was sampled intermit- 

 tently. From these data, I estimated that several mil- 

 lion age fish had left Coville Lake. 



The results of the sampling at Coville Lake in 1961 

 prompted further studies to answer the following ques- 

 tions: (1) Do significant numbers of age sockeye 

 salmon usually migrate from Coville Lake? (2) Do sig- 

 nificant numbers of juvenile sockeye salmon over- 

 winter in Coville Lake and migrate as age 1 smolts in 

 May and June? (3) Do the age sockeye salmon leav- 

 ing Coville Lake during the summer remain in Gros- 

 venor Lake until they become smolts, or do they con- 

 tinue downsystem to Naknek Lake their first summer? 

 (4) What is the cause of the presmolt migration? (5) Do 

 the behavior patterns of these fish resemble those of 

 smolts or fry, or are they unique to summer migrants? 

 Information pertaining to these questions was 

 gathered by the routine sampling of the Naknek sys- 

 tem and by special studies in Coville and Grosvenor 

 Rivers in 1962, 1963. and 1964, in addition to the sam- 

 pling in Coville River in 1961. 



Large and small fyke nets were both used to sample 

 migrating fish in the rivers. Although current ve- 

 locities were not measured, the small nets (1 m) were 

 fished in waters of about 0.3 meters per second (mps). 

 The large nets (1.2 x 1.2 m or 1.2 x 1.5 m) were 

 generally fished only in currents greater than 0.3 mps. 



Newly emerged fry could pass through the wings and 

 body of the large nets, but would be retained in the cod 

 end and by all parts of the small nets. The small nets 

 were usually fished from stakes driven into the 

 streambed and the large nets were fished from a cable 

 strung across the river. The cod end of the large fyke 

 net was often connected to a floating box (Craddock, 

 1961) that held the fish so that they could be released 

 alive and uninjured. 



In Coville River the estimate of the outmigration of 

 juvenile salmon is based on sampling with fyke nets 

 fished near the mouth where the river is about 24 to 46 

 m wide and 0.3 to 2 m deep; the current velocity is 



7 Wilbur L. Hartman. William R. Heard, and Charles W. Strick- 

 land. 1962. Red salmon studies at Brooks Lake Biological Field 

 Station, 1961. On file. National Marine Fisheries Service, Auke 

 Bay Fisheries Laboratory, Auke Bay. AK 99821, 53 p. 



n — I — I 1 — l — I — r 



234 1234 1234 



1961 1962 1963 



SEMIMONTHLY TIME PERIOD 



Figure 10. — Mean number of threespine sticklebacks per standard 

 tow in West End (units N-4, N-2, and N-l) by semimonthly time 

 periods, 1961-63. Time periods are: 1 — July 1-15; 2 — July 16-31; 

 3_August 1-15; 4— August 16-31. 



