312 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Analysis of these adult scales by Dr. Koo in- 

 dicated that all smolts migrated before they had 

 spent three winters in fresh water. In 1955 

 only 0.2 percent migrated from the lake as fry ; 

 in other years, no fry migrated. 



The proportions of Kvichak River smolts in 

 the two age groups during the 5 years of study 

 are illustrated in the length-frequency curves 

 of figure 13. The tabulated information re- 

 garding the daily sample size, the proportion of 

 fish having spent one winter in fresh water, and 

 the weighting values are shown in appendix 

 tables 8 through 12. 



Two relationships are apparent from these 

 data. First, a definite trend is present in 1955 

 through 1958 from fish that spent two winters 

 in fresh water to an increasingly dominant pro- 

 portion of fish that spent one winter in fresh 

 water. Then a complete reversal occurs in 1959 

 with dominance of the older fish. Additional 



1955 



5- 



5- 



o 

 a: 



80 90 100 no 120 



FORK LENGTH IN MILLIMETERS 



130 



Figure 13. — Composite length frequencies of smolts, 

 1955 through 1959. (Each daily sample is weighted by 

 magnitude of the fyke-net catches for that day. Total 

 frequency for each year is smoothed by moving aver- 

 ages of threes. The arrows indicate the division point 

 between age groups, as verified by scale samples.) 



years of data are necessary to establish the 

 presence or absence of cyclic changes. Second, 

 the modal length of the fish is related to popula- 

 tion density in the lake system before migra- 

 tion. In 1958, the year of greatest abundance in 

 Iliamna Lake, the mode of the fish that spent 

 one winter in fresh water was about 1 centi- 

 meter less than that of the one-winter fish of 

 other years. The same has been true of the 

 fish in the older age group in 1955 and 1959, 

 the next years of greater smolt abundance. The 

 length modes of both age groups in 1956 and 

 1957, years of low abundance, have been larger 

 or have been shifted to the right of the modes 

 of 1955, 1958, and 1959. This same relationship 

 has been reported in the Lake Dalnee red salmon 

 smolts by Krogius and Krokhin (1948). 



The relation between the smolt index catch 

 by age groups and the magnitude of the parent 

 escapement for each year of observation is 

 shown in table 11. It is concluded from the 

 data that large escapements have produced 

 large smolt migrations, and small escapements 

 have produced small smolt migrations. 



Smolt Sizes at Adjacent Net Sites 



In 1955 a comparison of smolt sizes was made 

 in the simultaneous catches of two nets set side 

 by side, 50 feet apart, at the index site. The 



Table 11. 



-Kvichak River parent escapements and 

 resulting smolt catches 



1 1952-1954 escapements estimated from spawning-ground surveys 

 by J. R. Gilbert and H. D. Smith. Since 1955, escapements estimated 

 by daily tower counts at Igiugie. 



- Number of winters the smolts spent in fresh water. 



