stock releases were made by pumping the test fish 

 down the penstock air vent through a 76-mm. 

 hose. 



In 1964, about 1,570 hatchery-reared juvenile 

 Chinook salmon and an equal number of juvenile 

 coho salmon were released into the spillway and 

 turbine penstocks to determine efficiency of the 

 traps at the Interstate Bridge (table 1). Fifteen 

 chinook and 15 coho salmon were recaptured, 

 (0.95-percent return for each species). Trapping 

 eflSciency for chinook salmon was slightly higher 

 in 1965 when 1,171 hatchery-reared test fish were 

 released and 15 fish (1.28 percent) were recaptured 

 (table 2). Recovery efficiency of the traps for 

 hatchery-reared sockeye salmon fingerlings re- 

 leased in 1965 was significantly higher than for 

 chinook salmon; 2,670 test sockeye salmon were 

 released and 71 (2.66 percent) were recaptured at 

 the bridge site (table 3). 



The scoop traps were more efllicient in the tur- 

 bine tailrace than at the Interstate Bridge. In 

 1964-65, 8,471 test fish (hatchery-reared juvenile 

 chinook, coho, and sockeye salmon) were released 

 into the various turbine penstocks for recovery 

 in the turbine tailrace. Differences in average 

 recovery between years and among species were 

 so slight that the data were combined. Recoveries 

 for daylight releases (8:00 a.m. to 4:00 p.m.) were 

 0.5 to 7.5 percent and averaged 4.1 percent (table 

 4). Recaptures of fish from night releases (4:00 

 p.m. through 8:00 a.m.) were 4.5 to 29.7 percent 

 and averaged 11.3 percent (table 5). 



METHODS OF COMPUTING EMIGRATION 



Estimates of emigration were based on live and 

 dead fish caught in the scoop traps. Identity of 

 the various populations was determined from fish 

 that had been marked in the tributary drainages 

 and subsequently recovered in the scoop traps. 

 Length-frequency data and scale samples were 

 also used to determine the origin of different 

 populations of fish emigrating at various times of 

 the year. 



Estimates of emigration during periods of 

 sampling at the Interstate Bridge were computed 

 with the general formula (Chapman, 1948) : 



where 



j^_CiM±l) 

 '"'- (R+1) 



A7^= population estimate 

 6*= sample size 

 Af =number of marks 

 i2=marked recaptures in C 



(1) 



Table 1. — Numbers of marked juvenile chinook and coho 

 salmon recovered in scoop traps at the Interstate Bridge 

 after release in the spillway (S) or turbines {T) of Brown- 

 lee Dam, April S4 to June SO, 1964 



Date (1964) 



Fish Release Average 

 released site spill 



Fish recovered 



Number 



April: 



24 101 S 



25 100 S 



26 103 8 



27 95 S 



28 100 S 



29 100 S 



May; 



7 106 S 



7 89 T 



8 100 S 



8 100 T 



15. 100 T 



16 100 T 



20 102 S 



20 100 T 



21 116 T 



27 106 T 



June: 



11 79 8 



14 179 8 



15 189 S 



16 200 S 



16. 200 T 



17 100 T 



18 100 T 



19 100 T 



23 100 S 



24 100 S 



25 100 S 



30 100 S 



Total 3,165 



(M .>/»«.) Number Percent 



177 

 185 

 279 

 405 

 458 

 452 



548 

 548 

 642 

 642 

 510 

 510 

 579 

 579 

 551 

 



332 



706 



737 



795 



795 



978 



1,100 



1,136 



1,189 



1,137 



961 



170 



0.99 

 1.00 

 .97 

 .00 

 .00 

 1.00 



3.77 

 4.49 



.00 

 1.00 



.00 

 2.00 



.98 



.00 

 1.72 



.94 



1.27 

 .56 

 1.06 

 1.00 

 .60 

 .00 

 1.00 

 1.00 

 .00 

 1.00 

 1.00 

 .00 



30 



.95 



Table 2. — Numbers of marked juvenile chinook salmon 

 recovered in scoop traps at the Interstate Bridge after 

 release in the spillway (S) or turbines (T) of Brownlee 

 Dam, April 9 to May 20, 1966 



To compensate for the variation in efficiency of 

 traps in the turbine tailrace, I computed emigra- 

 tion during periods of sampling at that site with 

 an alternate method: 



N,= 



trap catch 



percentage of efficiency 



(2) 



248 



Upper and lower limits were computed for esti- 

 mates of emigration at both sampling sites. For 

 estimates based on sampling at the Interstate 



U.S. FISH AND WILDLIFE SERVICE 



