TABLE 1. — Four -day counting schedule at Rock Island Dam, 1959 

 [x - indicates time of counting] 



half the peak annual count of 50,713 

 in 1957 (table 2). Maxinnum day's count 

 in 1959 was 1,528 fish on May 25 

 (table 3). 



Tables 4 and 5 show seminnonthly 

 totals of number and percentage of 

 Chinook count which ascended each fish 

 ladder. 



tified by considering all chinooks 18 

 inches or less in length prior to July 1 

 as jacks, and all chinooks 22 inches or 

 less in length subsequent to June 30 as 

 jacks. Maximum day's count in 1959 of 

 Chinook jacks occurred on May 25 

 (table 3). The 5,960 fish recorded as 

 jacks constitute 25.5 percent of the 

 total 1959 Chinook run. 



Chinook Salmon Jacks 



Some Chinook salmon return from the 

 ocean during the year following their 

 seaward migration and are referred to 

 as "jacks". These fish are predomi- 

 nantly males, and are smaller than the 

 average. It has been determined at 

 Rock Island Dam that up to June 30 of 

 each year jacks rarely, if ever, exceed 

 18 inches in length while the balance 

 of the fish appreciably exceed that 

 length. Likewise from July 1 to the end 

 of the season jacks rarely, if ever, 

 exceed 22 inches in length. Conse- 

 quently, jacks at Rock Island are iden- 



Sockeye Salmon, Oncorhynchus nerka 



(blueback or red) 



The sockeye count of 72,351 for 1959 

 was greater than the 26-year mean of 

 52,073 (table 2). In 1959, peak of the 

 run was reached on July 28, when 4, 081 

 fish were counted past the ladders at 

 Rock Island Dam. 



In recent years attention has been 

 drawn to the many small blueback both 

 at Bonneville and Rock Island Dams. 

 During the 1959 counting period at Rock 

 Island Dam sockeye under 16 inches in 



