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-f requenc ies 

 (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 



---> RQ oercent of the fish to be in 

 --*■ ninde in the 



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 

 annulus 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 smnulus was 

 noted. 



Chinook salmon . — Figure 23 shows two 

 size and age groups were present in the Chi- 

 nook sample for April and May. No fish from 

 the fingerling size group appeared in the 

 sample after May. The progressive growth by 

 month of the fry group is graphically illus- 

 trated. The small size group of fry consti- 

 tuted 21 percent of 3,318 chinook migrants 

 captured during April and May of 1955. 



Scale readings of 79 fish from the 

 <^ineerling group revealed 78 fish in their 

 -„„ fish in its third year. 

 ■- length, 



70 



? 60 

 u. 



° 50 



o 40 



S 



30 

 20 

 10 



7-8pm 8-9 9-10 



ONE HOUR PERIODS 



10-11 



11-12 



; 70 



60 

 50 

 40 

 30 

 20 

 10 



.744 



■411 



i 50 55 60 65 70 75 BO 85 90 95 100 05 110 115 120 125 130 05140 145 00155160 165 170 175 

 LENGTH IN MILLIMETERS 



Figure 21.— Time of day of migration - 

 steelhead trout. Tumwater Dam, 1955. 



Figure 22.— Length frequency of blueback 

 salmon migrants. Tumwater 

 Dam, 1955-1957. 



15 



