hibited a preference for nighttime migration 

 past Tumwater Dam although, as for blueback 

 and Chinook, they were taken in the trap 

 throughout the 24-hour period of a day. 

 During the spring season, April-May, com- 

 bined hourly counts indicated no pronounced 

 one hour preference, figure 21. 



For the summer and fall months a night- 

 time preference was also shown by the steel- 

 head. Upon adjustment for equal fishing 

 effort, the counts showed that 89 percent 

 of 615 fish recorded were counted in the 

 morning and 11 percent in the evening prior 

 to darkness. 



Length and Age Composition 



Blueback salmon . — Length-frequencies 

 (fork length) of blueback measured in 1955 

 and 1956 are shown in figure 22. Migrants 

 in 1955 are noticeably larger than migrants 

 of 1956. Scales of 664 blueback taken in 

 1955 showed 89 percent of the fish to be in 

 their second year (the dominant mode in the 

 figure) and 11 percent to be in their third 

 year. One fish was 163 mm. in length and 

 in its fourth year. A smaller Seunple of 

 235 fish in 1956 revealed 96 percent in 

 their second year and 4 percent in their 

 third year. No fish in its fourth year was 

 sampled this season. A few fry blueback, 

 or fish in their first year, that did not 

 occur in the measured sample were captured 

 in the spring. Only 34 of these fry, mea- 



80 

 70 

 60 

 50 



m 40 



30 



20 



10 







N = 189 



7-8pm 8-9 9-10 10-11 



ONE HOUR PERIODS 



suring about 35 mm. in length, were observed 

 out of a total of 51,533 blueback captured. 



Scale readings of the small number of 

 blueback taken during October revealed no 

 cuinulus had been formed, thus these large 

 fish, averaging 133 mm. , were fish in their 

 first year. Possibly these were hatchery 

 reared fish that had been released in the 

 lake a few days previous to their capture 

 at Tumwater. A few scales from these hatch- 

 ery fish were examined and no annulus was 

 noted. 



Chinook salmon . — 

 size and age groups we 

 nook sample for April 

 the fingerling size gr 

 sample after May. The 

 month of the fry group 

 trated. The small siz 

 tuted 21 percent of 3, 

 captured during April 



Figure 23 shows two 

 re present in the chi- 

 and May. No fish from 

 oup appeared in the 

 progressive growth by 

 is graphically illus- 

 e group of fry consti- 

 318 Chinook migrants 

 and May of 1955. 



Scale readings of 79 fish from the 

 fingerling group revealed 78 fish in their 

 second year and one fish in its third year. 

 This third year fish was 123 mm. in length, 



1955 N=744 



1956 N:4II 



11-12 



) 45 50 5S 60 65 70 75 80 95 90 95 100 05 110 H5 120 125 130 135 140 145 60155160 165 170(75 

 LENGTH IN MILLIMETERS 



Figure 21. --Time of day of migration - 

 steeUaead trout. Tumwater Dam, 1955 . 



Figure 22. --Length frequency of blueback 

 salmon migrants. Tumwater 

 Dam, 1955-1957- 



15 



