in 1956 was 67,000 fish, or 72 percent 

 of the Rock Island Deun counts. In 

 1957 the estimate was 43,000 blueback 

 or 60 percent of the Rock Island Dam 

 counts. 



Steelhead trout . --Two groups of 

 steelhead runs pass Rock Island Dam, 

 the spring run, which pass in mature 

 condition and are destined to spawn that 

 same season, and the fall run, which 

 pass Rock Island from July through 



700 



October and forms the larger group 

 of the two, figure 4. As counting at 

 Rock Island Dam is not continuous dur- 

 ing winter months but consists of 

 periodic counts at the three ladders, 

 the migration during this period is not 

 fully known. These periodic counts at 

 the various ladders at Rock Island have 

 revealed some movement of steelhead 

 throughout the winter months. Pre- 

 sumably, spawning of steelhead occurs 

 throughout the accessible river systems 



600 



500 



X 



400- 



ir 

 ui 

 o 



2 



300 



200- 



100 



1954 

 1955 



N = 4578 

 N = 3200 

 N = 1531 



1956 



1957 N =3927 



( Counts are for periods of confinuous 

 counting at the 3 ladders.) 



-•^..^p,,,, •••- — ^-~ 

 7 14 21 28 4 II 18 25 2 9 16 23 30 6 13 20 27 3 10 17 24 I 8 15 22 

 MAY JUNE JULY AUGUST SEPTEMBER OCTOBER 



Figure 4.--Steelhead trout counts at Rock Island Dam, 1954-57. (totals bf weeks). 



6 



