MAJOR and PAULIK: ENCROACHMENT OF WANAPUM DAM RESERVOIR 



Table 12. — Tag releases, tag observations, and travel times for sockeye salmon seen 

 passing over fish ladders at Rock Island Dam, 1954 and 1955. 



Period 



Number of fish 



togged and 



released 



1954 



IV 



1955 



III 



IV 



22 



119 

 155 



272 

 146 



246 

 89 



174 

 262 



123 



59 

 46 



298 

 227 



129 

 24 



93 



177 



The number observed may exceed the number tagged. See text (p. 132) for explanation. 



Percentage Observed 



The overall percentages of tagged sockeye 

 salmon observed passing Rock Island Dam in 

 1964 and 1965 (94.1 and 91.8, respectively) were 

 significantly higher than those recorded in 1954 

 and 1955 (79.2 and 67.4). A similar change 

 was noted for chinook salmon. As we mentioned 

 earlier in discussing the results with chinook 

 salmon, two factors — increased tag retention and 

 improved facilities for observing and reporting 

 tagged fish — probably contributed to the in- 

 creased percentages of tagged fish that were 

 observed. Unlike chinook salmon, for which a 

 greater part of the increased percentage of fish 

 sighted could be attributed to fish released on the 

 right bank, the improvement in sockeye salmon 

 was of the same magnitude for releases made 

 on both banks. 



Distribution by Ladder 



Percentages of tagged sockeye salmon in the 

 left ladder were 55.3, 64.3, 55.6, and 53.1 in 1954, 

 1955, 1964, and 1965, respectively. For the 



right ladder, the percentages were 13.2, 12.4, 

 23.7, and 23.3; for the center ladder they were 

 31.5, 23.3, 20.7, and 23.6. As with chinook salm- 

 on then, the distribution of tagged sockeye 

 salmon by ladder in postencroachment years, 

 1964 and 1965, did not differ significantly or at 

 least consistently so from that observed in pre- 

 encroachment years, 1954 and 1955. 



Travel Time from Release to Observation in 

 Fish Ladders 



Comparisons of the mean travel times by 

 period and area of release for 1954 versus 1964 

 and 1965 and for 1955 versus 1964 and 1965 

 are presented in Figure 5. On only 1 of 34 oc- 

 casions was the travel time in the preencroach- 

 ment tagging year less than for the correspond- 

 ing postencroachment tagging year. The dif- 

 ference was not significant. 



As with chinook salmon then, we found the 

 time required by tagged sockeye salmon to pass 

 the fish ladders at Rock Island Dam was con- 

 siderably less after the onset of encroachment 

 than before. 



139 



