COUNTING PROCEDURES 



Fish counting at Rock Island Dam in 

 1959 began on May 4 and terminated on 

 Septennber 30. From May 4 through 

 July 15 counting was conducted on a 

 "sample count" basis.' From July 16 

 to September 19 counting was on a 

 full-time basis (16 hours per day). 

 During the sample or "spot count" 

 period gates at che fish countin" weirs 

 remained open at all times to permit 

 unrestricted passage of upstream mi- 

 grating fish. 



In developing a sample count system 

 a study was made of past counting 

 records at Rock Island Dam. During 

 1954-55 conditions were fairly stable 

 at the dam and fish count data for these 

 2 years were used in developing the 

 sample count system. During this 

 period there were no experiments being 

 conducted to materially affect move- 

 ment of fish. 



From study of past count records the 

 following procedure for sample count- 

 ing was developed: 



1. Period May 4- July 15 was divided 

 into 18 4-day periods with 1 day 

 left over. 



ing periods at right and center 

 ladders. 



5. Each day the counter started at a 

 different ladder, alternating be- 

 tween the three. 



6. Four-day counting schedule (table 

 1). 



7. Estimated number of fishpassing 

 over left ladder on any 16-hour 

 day or 4-day cycle w^as computed 

 as follows : 



a. Number counting periods - 8 



b. Duration of each counting 

 period - 45 minutes (.75 of an 

 hour) 



c. Total hours of counting - 8 k 

 .75 = 6 hours 



d. Number of fish counted during 

 8-hour period - N 



e. Average number of fish per 

 hour - N -^ 6 



f. Number hours fishway 

 open - 16 



2. Counting gates were open from 

 4:00 a.m. to 8:00 p.m. 



3. Within each day of the 4-day 

 periods there were 16 counting 

 periods of 45 minutes each, be- 

 ginning on the hour and ending 

 45 minutes past the hour. This 

 allowed 1 5 minutes for the counter 

 to move to the next ladder. 



4. On each day of 4-day periods 

 fish were enumerated 8 counting 

 periods at left ladde r and 4 count- 



'System of sample counting was developed by Bio- 

 metrics Section, Bureau of Commercial Fisheries, U^. 

 Fish and Wildlife Service, Seattle, Wash. 



g. Total estimated number of 

 fish - 16 X e. 



Estimated numbers of fish pass- 

 ing right and center ladde rs wore 

 based on four counting periods of 

 3 hours each. 



ENUMERATION OF FISH 



Chinook Salmon Oncorhynchus tshawytscha 



The Chinook salmon count in 1959 of 

 23,352 is well above the mean of 

 14.838 for the 26-year period 1933- 

 1958. However, the count declined from 

 that of 1958 and was a little less than 



