20 

 10 







uj 20 

 a. 



10 - 



2 



o 



S20 



li- 10 

 o 



S 



S20 



10- 





 20 

 10 



1959 



Al 



n = 1305 

 x = 125.5 



I960 



1961 



n= 653 

 x= 127.0 



ttL 



1962 



n=238 

 X = 134.0 



1963 



I I I — I ' 1 

 90 100 110 



n=5IO 

 x= 132.6 



120 130 140 150 160 

 FISH LENGTH (MM.) 



170*170 



Figure 6. — Length-frequency distribution of Yakima 

 River spring chinook salmon captured during their 

 seaward migration at Prosser, 1959-63. 



Table 3. — Mean length, mean weight, condition factor, and 

 size of samples of spring chinook salmon taken at Prosser, 

 1959-63 



Date (week ending) 



Fish 



Mean fork 

 length 



Mean Condition 

 weight factor 



number migrating on day (i), Ci is the number 

 captured in the trap on day (i), and fi is the esti- 

 mated flow ill cubic meters per second of the 

 Yakima River at Prosser on day (i) (U.S. Geolog- 

 ical Survey, 1961-65). Canal flow is constant at 

 32.5 m.^ per second. This method requires the 

 assumptions that the number of fish per volume 

 of water is the same in the canal as in the river 

 and that the mortality in the canal is the same as 

 that in the adjacent stretch of river. The number 

 of migrants that were caught in the trap and the 

 total number that we estimated to have migrated 

 seaward at Prosser are shown in figure 10 by day 

 and year. 



Estimates of the number of seaward migrants, 

 estimates of the number of eggs deposited in 

 the appropriate brood year, and the percentage 

 survival are shown in table 4 and figure 11. 

 Survival ranged from 5.4 to 16.4 percent; the 



T.A.BLE 4. — Egg-to-migrant survival of young spring chinook 

 salmon in the Yakima River {brood years 1957-61) 



average was 10.7 percent. The low survival of the 

 1957 brood was caused — to a great extent — by 

 an unnatural condition that did not recur in the 

 other years. In 1957 an estimated 30 to 50 percent 

 of the eggs deposited in the upper Yakima River 

 subarea succumbed to exposure when, in October 

 and November, the water level was artificially 

 lowered and maintained 2 feet below what it had 



354 



U.S. FISH AND WILDLIFE SERVICE 



