conform to hours of daylight available, count- 

 ing was reduced to 14 hours each day, start- 

 ing at 5 a.m. and ending at 7 p.m. From 

 October 1 to October 9, counting was further 

 reduced to 8 hours each day, starting at 8 a.m. 

 and ending at 4 p.m. From October 10 to Octo- 

 ber 27, counting was conducted from 8 a.m. to 

 5 p.m., with 1 hour closure of gates at noon. 



A 15-minute rest period was allowed at the 

 end of each hour, and during all periods of 

 noncounting, ladders were closed to passage 

 of fish. 



ENUMERATION OF FISH 



Chinook Salmon, 



Oncorhynchus tshawytscha 



The Chinook salmon count in 1961 of 33,067 

 (jacks included) was well above the mean of 

 15,560 for the 28-year period 1933-61. The 

 count increased over the 1960 run and was a 

 little more than half the peak annual count of 

 50,713 in 1957 (table 1). Monthly totals of 

 Chinook salmon counted are given in table 2. 

 Maximum day's count of Chinook salmon, jacks 

 not included, in 1961 was 692 on August 7 

 (table 3). Tables 4 and 5 show semimonthly 

 totals of number and percentage of Chinook 

 salmon count which ascended each fish 

 ladder. 



Chinook Salnnon Jacks 



Some Chinook salmon return from the ocean 

 during the year following their seaward migra- 

 tion and are referred to as "jacks." These 

 fish are predominantly 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 ap- 

 preciably 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 Dam are identi- 

 fied by considering all Chinook salmon 1 8 inches 

 or less in length prior to July 1 as jacks, and 

 all Chinook salmon 22 inches or less in length 

 subsequent to June 30as jacks. Maximum day's 

 count of Chinook salmon jacks was 199 and 

 occurred on September 18 (table 3). The 9,260 



fish recorded as jacks constitute 28.0 percent 

 of the 1961 Chinook salmon run. 



Table 5 shows number and percent of chinook 

 salmon jack count which ascended each fish 

 ladder. Monthly totals are given in table 2. 



Sockeye Salmon, Oncorhynchus nerka 

 (blueback or red) 



The sockeye salmon count of 19,233 for 1961 

 was less than half the 28-year mean of 53,079 

 (table 1). In 1961 peak of the run was reached 

 on July 14, when 1,289 fish were counted 

 through the fishways at Rock Island Dam. 



In recent years attention has been drawn to 

 the many small sockeye salmon appearing at 

 Rock Island Dam. During the 1961 counting 

 period at Rock Island Dam sockeye salmon 

 under 16 inches in length were enumerated as 

 small fish. Number of sockeye salmon re- 

 corded as "small" was 3,497 (6.6 percent). 



Tables 6 and 7 show semimonthly totals of 

 number and percentage of sockeye salmon 

 count ascending each ladder. Of the sockeye 

 salmon passing Rock Island Dam in 1961, 

 65.6 percent ascended the left ladder, while 

 9.9 and 24.5 percent ascended the middle and 

 right ladders, respectively. Data pertaining to 

 sockeye salmon daily counts are contained in 

 tables 9-14. Monthly totals of sockeye salmon 

 counted in 1961 are given in table 2. 



Coho Salmon, Oncorhynchus kisutch 

 (silver) 



The coho salmon count of 50 fish in 1961 was 

 slightly less than the 28-year mean of 61, and 

 sligthly more than half the 1960 count (table 1). 

 Additional data are shown in tables 11 and 12. 

 Maximum day's count of 8 fish occured on 

 October 4 (table 2). 



Steelhead TTO\iX,Salmo gairdneri gairdneri 



The steelhead trout count of 7,042 in 1961 

 was well above the 28-year mean of 3,063 

 (table 1). 



Additional data pertaining to steelhead trout 

 daily counts are contained in tables 7-12. 



