considerable overlap of the two runs at 

 Tuinwater. Therefore, the tendency towards 

 a double mode in figure 4 may not necessari- 

 ly relfect the comparative abundauice of the 

 two groups. Jack chinook appear throughout 

 the season and are found in both the spring 

 chinook and summer chinook runs. 



Steelhead trout . — Steelhead trout pass- 

 ing Turawater Dam are known as fall steel- 

 hccid. Steelhead in the upper Columbia River 

 are designated as fall or spring steelhead 

 according to the time they pass Rock Island 

 Dam. Fall steelhead pass the dam from July 

 to November and are destined to spawn the 

 following spring. Spring steelhead pass 



during the spring months and spawn that 

 ssime spring. The weekly counts of steel- 

 head at Tumwater for 1955-57 (figure 5), 

 reveal the largest migration to be from 

 August to October. In 1955 counting did 

 not commence early enough to determine if 

 the spring migration occurred this season. 

 Although no well-marked spring migration 

 was noted in 1956, there was a substantial 

 migration of steelhead at Tumwater in the 

 spring of 1957. This 1957 migration was 

 believed to be composed of fish from the 

 1956 fall migration at Rock Island for two 

 reasons: (1) the spring steelhead run 

 peaked at Tumwater prior to the spring 

 steelhecid season's peak at Rock Island and 



1955 

 1956 

 1957 



12 16 

 JUNE 



10 14 Is ZZ 26 30 3 7 II 15 19 Z3 27 31 

 JUL'V AUGUST 



8 IZ 16 20 24 Z8 2 

 SEPTEMBER 



6 10 14 



Figure h. — Upstream migration - chinook salmon. Tumwater Dam, 1955-1957' 



