061-PROBABLE 

 TOTAL 



5 10 15 20 25 30 

 SOCKEYE SALMON FRY PER HECTARE (THOUSANDS) 



Figure 7. — Production of sockeye smolts resulting from 

 various fry densities. Little Kitoi and Ruth Lakes, 

 1955-61 brood years. 



assumed for Little Kitoi Lake. The shape of 

 the curve for Little Kitoi Lake would not 

 differ greatly from that of the curve for Ruth 

 Lake even if the average egg-to-fry survival 

 were actually much greater or much less 

 than 30 percent. The maximum probably would 

 still occur near the 5,000-fry recruitment. 

 Hence, it appears that in both lakes the opti- 

 mum density of fry, in terms of numbers of 

 smolts produced, is about 12,400 per surface 

 acre (I assume that the low survival of the 

 1960 plant in Ruth Lake was due to over- 

 stocking). 2 



Growth 



The first seaward migration of sockeye 

 smolts from Ruth Lake occurred in 1957 as 

 a result of the fry introduced in 1956. These 

 fish averaged 101 mm., fork length. The 

 corresponding age group of smolts migrating 

 from Little Kitoi Lake averaged 63 mm. 

 (table 7), and those from Midarm Lake aver- 

 aged 72 mm. (table 8). Table 7 compares the 

 average size of smolts of various age groups 

 from the fry plants from Ruth Lake in 1956-60 

 with the corresponding smolts from the natu- 



As the final work on this manuscript is being done, 

 the migration of 1-annulus sockeye smolts from one 

 further fry release into Ruth Lake is almost completed. 

 In 1963, 250,000 sockeye fry (of the 1962 brood year) were 

 released in Ruth Lake — a density of about 13,000 fry per 

 hectare. By fall 1964, after the downstream migration of 

 smolts resulting from this fry release was complete, 

 88,880 smolts had passed through the weir. The migration 

 of 88,880 as 1-annulus smolts indicates a minimum sur- 

 vival from fry-to-smolt stage of 36 percent, or about 

 4,630 smolts per surface hectare. As shown in figure 7, this 

 production is far above the top of the hypothetical curve 

 and coincides with the level of optimum fry density in 

 terms of smolt production as reflected by the Ruth Lake 

 experiments. 



rally maintained stock in Little Kitoi Lake. 

 Figure 8 shows the average length of smolts 

 of all ages of each brood year from Ruth and 

 Little Kitoi Lakes. Figure 9 shows a similar 

 comparison based on the year of downstream 

 migration rather than the parent brood year. 

 This latter comparison is more suitable for 

 studying the effects of environment. Annual 

 fluctuations in the size of 1- and 2-check 

 smolts are similar, but fluctuations in the 

 size of 3-check smolts are almost directly 

 the opposite of those of the two younger age 

 groups. The number of 3-annulus smolts each 

 year is small, however. The fact that in each 

 of these two lakes the two age groups that 

 make up the bulk of the migration each year 

 follow the same general annual growth fluc- 

 tuations suggests that the environment, as 

 well as density of fish, plays an important part 

 in determining growth. 



The density or potential density of fry in 

 the lakes was correlated with the size of 

 resultant smolts in both lakes (fig. 10). The 

 highest fry releases into Ruth Lake and the 

 largest potential egg deposition in Little Kitoi 

 Lake resulted in the smallest smolts of all 

 ages, and vice versa. The single exception 

 was offered by 3-check smolts resulting from 

 the release of the 1959 brood year into Ruth 

 Lake. This release, the largest in the lake, 

 produced the largest 3-check smolts. The fry 

 release of 1960 (1959 brood year) was the last, 

 however, into Ruth Lake until 1963; as a re- 

 sult, fry that remained for 3 yr, in the lake 

 before migrating had ideal conditions for 

 growth during their third growing season. 

 Only 108 smolts left Ruth Lake after 3 grow- 

 ing seasons, and these fish, discounting any 

 permanent holdover as kokanee, had the entire 

 lake to themselves during the last year- -about 

 five fish per hectare. 



Smolts resulting from the fry release of 

 1956 in Midarm Lake had sizes generally 

 comparable to those of smolts of similar age 

 from Little Kitoi Lake (tables 7 and 8). 



Further information on growth is supplied 

 by the mean number of circuli laid down by 

 juvenile sockeye in Little Kitoi and Ruth Lakes 

 during each year of the study (tables 9 

 and 10; fig. 11). Smolts from Ruth Lake laid 

 down an average of about 50 percent more 

 circuli than did smolts from Little Kitoi 

 Lake (table 11). The spring growth of smolts, 

 as measured by numbers of circuli, was over 

 100 percent greater in Ruth Lake than in 

 Little Kitoi Lake. 



In both lakes, the mean number of circuli 

 laid down in the spring was considerably 

 smaller in fish that had spent 1 or 2 addi- 

 tional years in lake residence; the 2-annulus 

 smolts had fewer spring circuli than had the 

 1-annulus smolts, and 3-annulus snnolts had 

 fewer spring circuli than had the 2-annulus 

 smolts. 



10 



