SUMMARY PM) CONCLUSIONS 



This study was begun in 19hl when the largest blueback salmon spawr.ing 

 escapement since 1938 brought concern as to whether or not remaining spaLm- 

 ing and rearing grounds were adequate. Suitable blueback salmon spawning 

 areas have bsen greatly reduced by the construction of water-use projects. 



Paralleling the gradual loss of rearing areas available has been a 

 general downward trend in the commercial catches. An all-time low was 

 experienced in 19U5. This has been followed by increased runs in recent 

 years, most noticeably at Rock Island Dam where a counting station has 

 been maintained and where an estimate of the spawning escapement can be 

 made. 



The main objectives of the 19h7-U9 and 19^1 blueback studies were to 

 determine the success of natural spasming under anticipated conditions of 

 overcrowding, A system based on averages was applied to the counts which 

 gave estimates for total spawning populations,, Relating these estimates 

 to data obtained on the number of square yards of gravel available as 

 determined by stream surveys and applying a given square-yard gravel require- 

 ment for spawning bluebacks provided data to support the conclusion that there 

 was no overcrowding, and this conclusion was borne out by observations. In some 

 instances there were concentrations of fish on certain spawning riffles while 

 other apparently suitable gravels remained unoccupied. It has been shown 

 that the available gravel vras more than adequate for the number of spawners 

 in the Wenatchee system. The presently available spawning grounds in the 

 Okanogan system could support a run approximately four times the number of 

 fish estimated in the run of I9U8. 



Regular examinations of sample nests were made during the winter of 

 19ii7-U8 to observe progress of the young bluebacks and study environmental 

 conditions. 



A study of predators in Lake Wenatchee revealed that youn.g salmon were 

 being preyed upon by squawfish and Dolly Varden trout. 



Owing to imminent construction of additional dams within the Colujribia 

 River system it is recommended that new waters be experimentally planted with 

 blueback salmon. Data from this type of research would be useful in future 

 planning for development of Columbia River blueback salmon runs. 



Prospects for future Columbia River blueback runs depend on a number of 

 factors. The dangers to the developing eggs of severe winter conditions ^ 

 the losses of young due to predators and competitors in the rearing areas, 

 and ijnscreened water diversions along their downstream migratory routes, the 

 mortality of upstream migrant adults due to low water and high temperatures^ 

 all have been discussed. Another factor which will affect the future escape- 

 ments is the intensity of the commercial fishery in the lower river o Good 

 catches will undoubtedly attract more fishermen to the blueback fisherj' and 

 thereby increase the fishing intensity for the blueback salmon, allowing a 

 correspondingly smaller spawning escapement. The 19^0 and 19^1 escapements 

 show a continued increase^ with the Rock Island count of 19^0 exceeding its 

 cycle j'-ear by !p,018 fish and the 19^1 count establishing an l8-year record 



of 101,682 blueback salmon over the dam. 



28 



