tagging, although half the fish were tagged on 

 July 15. There was no way for the counters to 

 distinguish between the two lots. Correctly then, 

 many fish passed 1 day sooner than indicated. 

 It is notable that these results are similar to those 

 from the Rock Island experiments in which the 

 majority of fish passed in 2 to 4 days. 



Figure A-2 shows the days-out by ladder at 

 Bonneville. Many fish (44 percent) crossed the 

 river to pass upstream through the Bradford 

 Island ladder, although the fish were trapped and 

 released on the Washington shore. The mean 

 days-out time for fish passing through the two 

 ladders was approximately the same: 6.6 days for 

 the Washington shore ladder and 6.8 days for 

 the Bradford Island ladder. Again, these results 

 were similar to those obtained at Rock Island. 



Tag Returns — Bonneville to McNary Dam 



Tag recoveries were obtained above Bonneville 

 Dam from the commercial fishery, sports fisher- 

 men, the Celilo Falls fishery, at McNary Dam, at 

 Rock Island Dam, and also from spawning ground 



Figure A-l. — Number of days-out at Bonneville of tagged 

 fish released below the dam, 1955 season (days-out 

 dated from July 14). 



surveys above Rock Island. For the area between 

 Bonneville and McNary Dams, 28 sockeye and 3 

 steelhead tags were returned by commercial 

 fishermen and the Indian dip net fishery at Celilo 

 Falls. Sports fishermen fishing in the various 

 tributaries returned tags from seven tagged steel- 

 head. 



At McNary Dam, approximately 120 miles 

 above BonnevUle, 84 of the Bonneville tagged fish 

 were recorded at counting stations. This was 



28.7 percent of the number tagged and 51.5 per- 

 cent of the number recorded over Bonneville 

 Dam. The total number of tags accounted for 

 from Bonneville to and including McNary counts 

 was 122, or 41.6 percent of the number tagged and 



74.8 percent of the number reported over Bonne- 

 ville. 



Figure A-3 shows the days-out for tagged fish 

 at McNary Dam. The double mode is pronounced 

 for each species and the modes are 5 days apart 

 for chinooks and sockeye. It is doubtful that the 

 5-day interval is the result of computing days out 

 from the first day of tagging when tagging oc- 

 curred on 2 successive days. It is more likely 

 that some short-term delay affected a group of 

 fish, possibly those tagged the second day. The 

 figure shows that the majority of tagged fish took 

 from 12 to 20 days to pass McNary Dam after 

 being tagged below Bonneville Dam. 



Tag Returns Above McNary Dam 



The Rock Island fish counters were alerted to 

 the particular tag applied at Bonneville and re- 

 corded its appearance on fish. The tags used 

 were paired disks of a copper color with a black 

 bullseye, a very distinctive color, and much 



DAYS-OUT 



Figure A-2. — Number of days-out by ladder at Bonne- Figure A-3. — Number of days-out at McNary Dam for 

 ville of tagged fish released below the dam in 1955 the three species tagged below Bonneville Dam in 1955 



(days-out dated from July 14). (days-out dated from July 14). 



LOSS AND DELAY OF SALMON PASSING ROCK ISLAND DAM 



367 



