MAJOR and PAULIK: ENCROACHMENT OF WANAPUM DAM RESERVOIR 



spill) for the two "experimental" releases on 

 August 3 and 5. 



The percentag-es of the tagged fish observed 

 in the right ladder were 15.9, 23.8, and 31.9 for 

 the releases of July 31 (0-day modified spill), 

 August 3 (3-day modified spill), and August 5 

 (1-day modified spill), respectively. Compara- 

 ble percentages were 19.5, 15.9, and 12.8 for 

 the center ladder and 64.6, 60.3, and 55.3 for the 

 left ladder. Travel times for the three releases 

 averaged 2.7, 4.4, and 3.6 half-days respectively. 

 Thus, it appears that spilling from the right side 

 tended to attract fish released on the left bank 

 to the right ladder but at the expense of in- 

 creasing overall travel time. 



The change in the spill pattern did not have 

 a significant effect on tagged fish released on 

 the right bank. For the July 30 "control" re- 

 lease, mean travel time was 4.6 half-days; for 

 the August 4 "experimental" release it was 4.6 

 half-days. Slightly more fish from the August 4 

 release (19.5^0 were attracted to the right lad- 

 der than from the July 30 release (12.69r). 



Most striking is the similarity between the 

 left-bank release of August 3 and the right-bank 

 release of August 4. The percentages of tagged 

 fish using various ladders for the releases of 

 August 3 and 4 were: (see Table 5) left, 60.3 

 and 64.6; center, 15.9 and 15.9; and right, 23.8 

 and 19.5. Overall travel times were 4.4 and 4.6 

 half-days. Travel times by ladder were similar 

 —4.4 and 4.8 half-days for the left, 2.8 and 3.3 

 for the center, and 5.6 and 5.6 for the right 

 ladder. 



In summary, the departure from the basic spill 

 pattern tended to attract fish to the right-bank 

 ladder, especially those released on the left bank 

 and in so doing, increased the overall travel time. 

 These experiments support the eflScacy of the 

 basic spill pattern as compared to the other pat- 

 tern tested. 



COMPARISON OF PREENCROACH- 



MENT AND POSTENCROACHMENT 



TAGGING STUDIES 



The effect of the encroachment of Wanapum 

 Reservoir on fish passage at Rock Island Dam 

 is best measured by comparing the results of 



the pre- and postencroachment tagging studies. 

 We shall consider spring chinook salmon first, 

 followed by sockeye salmon. Three measure- 

 ments — percentage observed, distribution by 

 ladder, and travel time — provide the basis of 

 our analysis. 



SPRING CHINOOK SALMON 



The results of the 1954 and 1955 tagging 

 studies with spring chinook salmon are presented 

 in Tables 10 and 11. Comparable data for 1964 

 and 1965 are in Table 2. 



Percentage Observed 



The overall percentages of tagged spring chi- 

 nook salmon observed passing Rock Island Dam 

 were 38.7 and 59.9 in 1954 and 1955; they were 

 90.3 and 91.6 in 1964 and 1965. Although some 

 of the significant increase may represent better 

 tag retention or increased survival brought 

 about by improved conditions for fish passage 

 during the postencroachment study, it is likely 

 that the precautions we took to improve the tag 

 observations also were important. 



It is interesting to note that the greatest in- 

 crease occurred for fish released from the right- 

 bank site. In 1954 and 1955, sightings from 

 right-bank releases were only 37.5 and 51.9%, 

 whereas in the postencroachment years — 1964 

 and 1965— they were 81.1 and 94.9%. Few fish 

 were released on the left bank in 1954, but the 

 increase in the percentage of tagged fish ob- 

 served for the other years (from 77.6 in 1955 

 to 95.5 and 88.4 in 1964 and 1965) while sig- 

 nificant, is not as dramatic as for the right-bank 

 releases. 



Distribution by Ladder 



The percentages of tagged spring chinook 

 salmon in the left-bank fish ladder were 61.7, 

 74.5, 46.2, and 66.3 in 1954, 1955, 1964, and 1965, 

 respectively. For the right ladder the percent- 

 ages were 25.0, 16.0, 21.5, and 15.4 for the 4 

 years, respectively. This means that 13.3% used 

 the center ladder in 1954, 9.6% in 1955, 32.3% 

 in 1964, and 18.2% in 1965. Thus, there was no 



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