reference to the problem of enumeration by means 

 of marked members. International Pacific Salmon 

 Fisheries Commission, Bulletin IV, 207 pp. 



Schonino, Robert W., and Donald R. Johnson. 



1956. A measured delay in the migration of adult 

 chinook salmon at Bonneville Dam on the Colum- 

 bia River. Fish Commission of Oregon, Contri- 

 bution No. 23, 16 pp. 



Thompson, William F. 



1945. Effect of the obstruction at Hell's Gate on 

 the sockeye salmon of the Fraser River. Inter- 

 national Pacific Salmon Fisheries Commission, 

 Bulletin No. 1, 175 pp. 



APPENDIX 



BONNEVILLE TAGGING EXPERIMENTS 



At the conclusion of the Rock Island tagging 

 experiments in 1954, we were confronted with 

 the apparent loss at the dam of many tagged 

 fish. What was the meaning of observing only 

 approximately 75 percent of the tags released 

 below the dam in 1954 and 64 percent in 1953? 

 In the following years, 65 percent in 1955 and 

 86 percent in 1956 of all tags released were 

 subsequently recorded by fish counters. Were 

 these percentage returns due to conditions as- 

 sociated with the Rock Island fishways or could 

 low percentage returns from tagging be expected 

 at any dam? In an attempt to answer these ques- 

 tions we decided to tag, on a small scale, below 

 another dam in the same manner as at Rock 

 Island. The objectives were to determine the 

 percentage and pattern of tag returns at Bonne- 

 ville Dam and compare them with the Rock 

 Island tagging data. 



On July 14 and 15, 1955, 293 fish were tagged 

 and released below Bonneville Dam located on the 

 Columbia River approximately 140 miles above 

 the river's mouth. The procedure at Bonne- 



Table A-l. — Returns at Bonneville Dam of tagged 

 salmon and steelhead released below the dam in 1955 



i This is an obvious errof in species identification. 



ville was the same as at Rock Island. Fish 

 were trapped in a ladder, transported by truck, 

 and tagged and released below the dam. The 

 experiments differed somewhat from those at 

 Rock Island in that the fish were released about 

 one mile below Bonneville on only one bank 

 while at Rock Island they were released about, 

 1,000 feet below the dam at both banks. Also, 

 fish at Bonneville were tagged with paired disks 

 and not the combination tags applied at Rock 

 Island. 



Tag Returns at Bonneville 



The number tagged and the returns at Bonne- 

 ville are shown in table A-l. Far more steelhead 

 were tagged at Bonneville than during the Rock 

 Island experiments. Tag returns of 55.6 percent 

 reported over Bonneville Dam by the fish counters 

 were less than for any season at Rock Island, 

 where percent returns ranged from 64 to 86 for 

 the seasons 1953-56. Nine tags were returned 

 from below Bonneville, six from dead fish found 

 on the beaches and three from fishermen. At Rock 

 Island the largest number of recoveries from 

 below the dam occurred in 1956 when seven were 

 recovered. Of these, five were from McNary 

 Dam where a trap was installed for other tagging 

 projects, one was returned by a sports fisherman, 

 and one was observed in Redfish Lake in the 

 Snake River system. 



One feature found at Bonneville and not at 

 Rock Island is the ship locks through which it 

 is possible for fish to pass. There was no way 

 of knowing whether or not any tagged fish passed 

 the dam by this means. 



As at Rock Island, the returns indicated fish 

 counters had trouble identifying species. This 

 is evident when 39 tagged chinook were reported 

 by the counters and only 17 had been tagged. 

 This same kind of error was noted at McNary 

 Dam where fish counters reported 23 tagged 

 chinooks from this same experiment. 



The time-out period (time elapsing between 

 tagging and observation at the counting boards) 

 for tagged fish at Bonneville was similar to re- 

 sults obtained at Rock Island. Figure A-l 

 shows the number of days-out for all tagged fish 

 observed at Bonneville. The majority of the 

 fish passed in 2 to 5 days after tagging. There is 

 an inherent error in the figure because days-out 

 were computed from July 14, the first day of 



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