different from the tag combinations used below 

 Rock Island. The counters reported five sockeye 

 and one chinook tag of this group between August 

 3 and August 21. However, the counters were 

 apparently unable to observe and identify this 

 particular tag easily, for 14 tags (11 sockeye, 2 

 chinooks, and 1 steelhead) were recovered during 

 spawning ground surveys above Rock Island. 



If many of the Bonneville tags (8 of 14 or 57 

 percent) passed Rock Island undetected, where 

 counters were alerted for tags of various colors and 

 combinations, it is likely tagged fish could pass 

 unnoticed at any dam. Unaccounted-for tags, 

 which have been released below a dam, may not 

 represent true mortalities of tagged fish occurring 

 below a dam. These data are dependent upon the 

 ability of fish counters to observe all tags, and for 

 various reasons this may not be possible. 



SUMMARY AND CONCLUSIONS 



A small-scale tagging experiment below Bonne- 

 ville Dam on July 14, and 15, 1955, and patterned 

 after the Rock Island experiments, gave results 

 similar to those obtained at Rock Island Dam. 

 Total tag returns at Bonneville Dam were 56 



percent, or somewhat less than the 64-86 percent 

 returns at Rock Island for 1953-56. It is not 

 known if tagged fish passed Bonneville by way of 

 the navigation locks, thus reducing the number 

 available for passage through the fishways. Fish 

 released on one shore below Bonneville passed the 

 dam through both fishways with only a slight 

 majority passing through the Washington shore 

 ladder on the side they were released. 



The days-out period at Bonneville compared 

 closely with the results obtained at Rock Island. 

 The majority of tagged fish passed in 2 to 4 days 

 at both dams. As at Rock Island Dam, the fish 

 counters at both Bonneville and McNary Dams had 

 difficulty in identifying species. More tagged 

 chinooks were reported at Bonneville and McNary 

 Dams than had been tagged. 



The returns at Rock Island of the Bonneville 

 releases were featured by the apparent inability 

 of the counters to identify these tags. Six tags 

 were reported at the dam and 14 were recovered 

 on the spawning grounds above the dam. It is 

 suggested, therefore, that tags may pass undetected 

 at any dam and caution must be used in relating 

 unaccounted-for tags to mortalities occurring 

 below a dam. 



368 



U.S. FISH AND WILDLIFE SERVICE 



