fish in August. Maximum day 1 s count of chinook 

 salmon (jacks excluded) was 896 on May 5 

 (table 3), as compared to 430 on August 5, 1963. 

 Tables 4 and 5 show semimonthly totals of the 

 number and percentage of chinook salmon 

 counted over each ladder. Of the chinook 

 salmon (jacks excluded), 51 percent ascended 

 the left ladder, while 28 and 21 percent 

 ascended the middle and right ladder s, respec- 

 tively. In 1963, percentages of chinook salmon 

 (jacks excluded) which used the left, middle, 

 and right ladders were 73, 14, and 13, re- 

 spectively. 



Table 3- --Maximum daily counts, salmon and 

 steelhead, Rock Island Dam, 1964 



Species 

 Chinook (except jacks) 

 Chinook (jacks). . . . 



Sockeye 



Coho 



Steelhead 



Date 



May 5 

 Sept. 12 

 July 27 

 Oct. 9, 22 

 Sept. 17 



Number 

 of fish 



257 



6,247 



5 



129 



Chinook Salmon Jacks 



Some chinook salmon return from the ocean 

 as mature fish in the year following their 

 seaward migration and are referred to as 

 "jacks." These fish are small and males 

 predominate. At Rock Island Dam in 1964, all 

 chinook salmon 24 inches or less were counted 

 as jacks. Each counting board has a marked 

 section, 24 inches long, for use of the counter 

 in gaging the length of these small chinook 

 salmon. The maximum daily count of 257 jacks 

 occurred on September 12 (table 3), three days 

 earlier than in 1963. The 14,493 fish recorded 

 as jacks constituted about 36 percent of the 

 total chinook run as compared to 56 percent 

 in 1963. 



Table 5 shows the number and percentage 

 of chinook salmon jacks counted over each 

 fish ladder. In 1964, 74, 14, and 12 percent 

 of the jacks used the left, middle, and right 

 ladders, respectively, as compared to 72, 11, 

 and 17 percent in 1963. Monthly totals are 

 given in table 2. 



Sockeye Salmon, Oncorhynchus nerka 

 (Blueback or Red) 



The sockeye salmon count of 69,41 1 was about 

 35 percent greater than the 31-year mean of 



Table 4. --Semimonthly number and percent of chinook salmon counted over each fish ladder, Rock 



Island Dam, 1964 



(Jacks not included) 



1/ Middle ladder closed from Oct. 14-24 in order to make repairs. 



3 



