Lake. The migration of larger fish may also be the 

 cause of the reversal between 20 August and 1 Sep- 

 tember of the relation between the average size of age 

 sockeye salmon in Iliuk Arm and the average size in 

 Coville Lake (Table 21). The average size of age fish 

 was smaller in Iliuk Arm than in Coville Lake on 20 

 August (1961, 1962, 1963), but by 1 September the fish 

 were larger in Iliuk Arm than in Coville Lake. 



Differences in size of fry at time of emergence. 



— Differences in the average sizes of fry produced by 

 different spawning groups within a system have been 

 documented (Raleigh, 1967; Brannon, 1967). McCart 

 (1967) considered the question of differences in size of 

 fry and suggested that they could result from differ- 

 ences in the size of adults and of eggs. Although de- 

 tailed study may reveal differences in the size of fry 

 within the Naknek system, the similarities of shape 

 and in location of peaks of length frequency graphs for 

 late July during this study do not indicate differences 

 in the size of fry at the time they leave the gravel. 



Species Commonly Associated with 

 Juvenile Sockeye Salmon 



Data on size, length frequency, and growth of 

 species commonly captured with juvenile sockeye 

 salmon in tow nets are too few to permit description of 

 growth. Therefore I discuss data ori length frequency 

 in some of the lakes for only three species — threespine 

 sticklebacks, ninespine sticklebacks, and pond smelt. 



Two to several age groups were present in the length 

 frequency samples of each associated species, usually 

 including age fish. The variation in the rate of cap- 

 ture of age fish with season and species and in year- 

 class strength from year to year makes it difficult to 

 compare the abundance either between species or 

 within a species at different times. 



Threespine sticklebacks. — The length frequencies of 

 threespine sticklebacks from nine samples collected 

 with tow nets from 1961 to 1964 are presented in Fig- 

 ure 25. Although these samples represent diverse 

 areas and times, two important facts were evident. ( 1) 

 Age threespine sticklebacks did not appear in tow 

 net catches in appreciable numbers until late August 

 when they ranged to about 30 mm fork length. When 

 sticklebacks hatch in early July they are about 5 mm 

 long and they grow to about 7 mm in their first week. 12 

 I substantiated these laboratory observations by visual 

 observations of small threespine sticklebacks close to 

 shore near the outlet of Coville Lake during seining 

 and diving in July 1963. (2) Although it is probable that 

 only two age classes other than age made up most of 

 the population, the older classes usually could not be 

 separated on the basis of length because of a broad 



12 Based on observations of progeny of a pair of threespine 

 sticklebacks from Brooks Lake that spawned in an aquarium. (W. 

 R. Heard, National Marine Fisheries Service, Auke Bay Fisheries 

 Laboratory. Auke Bay. AK 99821, pers. comm.) 



overlap in length offish assumed to be age I and older. 



These two general observations also appear to be 

 true for threespine sticklebacks in Karluk Lake and in 

 Bare Lake on Kodiak Island (Greenbank and Nelson, 

 1959) and in lakes of the Wood system (Rogers, 1968). 

 When comparing my data with those of Greenbank 

 and Nelson it appears that they overlooked the real 

 age fish when they did appear in the length frequency 

 graphs (only on 27 August 1954 for Bare Lake and 

 probably from 17 August to 13 September according to 

 length frequency histograms for fish from Karluk 

 Lake). As a result, Greenbank and Nelson may be 1 yr 

 off in assigning ages to fish represented by portions of 

 these histograms. Kerns (1961), however, was able to 

 separate age I threespine sticklebacks from age and 

 age II and older fish by length. 



European workers also have difficulty in separating 

 age groups of threespine and ninespine sticklebacks on 

 the basis of size distribution because of the slow 

 growth of the age I and older fish and a resulting over- 

 lap in size of the various year groups (Jones and 

 Hynes, 1950). 



The largest threespine stickleback I measured was 

 66 mm in fork length and came from West End. It 

 appears that few threespine sticklebacks survive after 

 spawning in their third or fourth summer. 



Ninespine sticklebacks. — Length frequency data are 

 available for only four samples of ninespine stickle- 

 backs (Fig. 26). It appears probable that three age 

 classes, 0, I, and II, are present in the length fre- 

 quency tabulations, but their definition by length is not 

 possible because of the broad overlap in length. Wal- 

 lace (1969) could not separate the age classes of nine- 

 spine sticklebacks from the Naknek system, although 

 he examined otoliths as well as length frequencies. A 

 higher proportion of ninespine sticklebacks than 

 threespine sticklebacks was in the 60 mm and greater 

 size groups. The relatively fewer ninespine than 

 threespine sticklebacks less than 36 mm may be due to 

 differences in habitat preference or size of age fish of 

 the two species. The ninespine sticklebacks were 

 more abundant than the threespine sticklebacks only 

 in the shallower water of Coville Lake. The largest 

 ninespine stickleback collected was 72 mm in fork 

 length. 



Pond smelt. — Length frequency data are presented 

 for four samples of pond smelt from Coville Lake and 

 one from West End in Figure 27. As with sticklebacks, 

 age pond smelt did not appear in the tow net catches 

 until late August. The fork length of 73 pond smelt 

 collected with a small-mesh dip net near the outlet of 

 Coville Lake on 18 July 1962 ranged from 26 to 48 mm. 

 These fish were probably all in their second summer. 

 It appears that at least three age classes, 0, II, and II, 

 are in the samples represented in Figure 27 and that 

 there is broad overlap in length of the age I and older 

 fish. 



44 



