spawning grounds subsequently were recovered. 

 Such double recoveries or observations result in a 

 tagged fish being counted two or more times in 

 recovery areas 2 and 3. 



To estimate the number of tagged individuals in 

 the recovery-observations totals, we use the 

 following expression: 



S=R2+R»+0 2 +O z -R a 



-f <«-(£) (t) (E -+ ' 



Where, for each tag release group (age-release area- 

 year combination), 



i? 2 = number of tagged fish recovered at Zosel Dam 

 R 3 = number of tagged fish recovered in area 3 



2 = number of tagged fish observed at Zosel Dam 

 3 = number of tagged fish observed in area 3 

 R 23 = number of tugged fish recovered at Zosel Dam 

 and also in area 3 



The first negative term corrects for double 

 recoveries of tagged fish; the second negative term 

 corrects for recoveries in area 3 of tagged fish 

 observed at Zosel Dam; the last negative term 

 corrects for observations in area 3 of tagged fish 

 recovered or observed at Zosel Dam. The quan- 

 tity, S, is referred to as the estimated total single 

 recoveries. 



Table 4 shows the recoveries, double recoveries, 

 observations, estimated duplicate recovery-obser- 

 vations, and estimated total single recoveries for 

 each release group. 



Table 2. — Sockeye salmon tagging data at Rock Island Dam 



[19541 



See footnotes at end of table. 



LOSS AND DELAY OF SALMON PASSING ROCK ISLAND DAM 



343 



