large leikes In the Okanogem chain pemit 

 great surface heating. 



Figure 2 also Illustrates the varia- 

 tion In temperature, 62' to Wf., during 

 the period of spawning- The peak of spawn- 

 ing occurred at a temperature of approxi- 

 mately 53'F. 



ratios in the two age classes as well as 

 the age -class composition of the entire 

 sample. The 32 's made up 30 percent of 

 the sample and had a sex ratio of 1 male 

 to 0.514- females while the k^'s made up 

 70 percent of the sample and had a sex 

 ratio of 1 male to I.62 females. 



CC»1P0SITI0N OF ESCAPEMENT 



A sample of 695 fish was measured on 

 the Okanogan spawning grounds. The length 

 frequency curve, figure 3> clearly indicates 

 the occurrence of the two age classes com- 

 prising the spawning population. Exami- 

 nation of the otoliths from 79 of these 

 fish disclosed that the dividing line 

 between the 32 's and 42's lies between 

 18 inches and iS-l/l*- inches for females 

 and between I8-I/2 inches and 18-3/^ Inches 

 for males (table h). This table also 

 demonstrates the divergence of the sex 



SPAWNING SUCCESS 



Table 5 is a record of a much larger 

 sample examined for sex and for spawning 

 success. A total of 2,046 fish were sexed, 

 and the females were examined for complete- 

 ness of spawning. The overall sex ratio 

 of medes to females in this sample was 1: 

 1.3^, and 92 percent of the females were 

 canpletely spawned. In 1955 and 1956 the 

 percentages of completely spawned fish 

 were 9'* and 95 respectively, which indi- 

 cates that the delays encountered by the 

 1957 spawners did not materially affect 

 their spawning success. 



Table 3* -'Distribution of blueback salmon above Rock Island dam 



1/ Factor 5 estimates through '52 and counts at Tumwater Dam thereafter. 



