FISHERY BULLETIN: VOL, 74, NO. 4 



Table 15.- Population estimates of juvenile coho salmon from mark-and-recapture experiments in Sashin Creek and Funny Creek, 



1964-67. 



'Estimates of population size in the whole of Sashin Creek were not made. 



were mainly progeny of the abundant 1963 

 spawners. 



Variations in average annual streamflow have 

 been shown to affect significantly the number of 

 juvenile coho salmon in Washington streams 

 (Smoker 1953), but in Sashin Creek, other factors 

 such as parent escapement, original number of 

 coho salmon fry, and competition probably have 

 more influence on determining the number of 

 juvenile coho salmon. Sashin Creek is located in an 

 area of heavy rainfall that has small variations in 

 the annual total precipitation and annual average 

 stream discharge. From 1964 through 1967, annual 

 precipitation ranged from 546 to 643 cm. Greater 

 variations in average stream discharge for a 

 specific month occur from year to year. Annual 

 variations in stream discharge during the 1-mo 

 period in midsummer when populations of juvenile 

 coho salmon decreased most rapidly do not appear 

 to be correlated with the rates of population 

 decline (Table 17). 



In 1965, 1966, and 1967, when estimates of 

 juvenile coho salmon populations were made in 

 each study area, the highest densities of coho 



salmon in Sashin Creek usually occurred in the 

 lower study area, which is characterized by slow 

 water. Densities of coho salmon fry and 

 fingerlings were even higher in Funny Creek, 

 another slow-water habitat (Table 18). 



Funny Creek was unique in our study areas in 

 that the populations of juvenile coho salmon 

 sometimes increased during the summer. The 

 estimated number of coho salmon fingerlings 

 increased from 251 to 389 between late June and 

 late July in 1966 (1964 brood year) and from 503 to 

 1,239 between mid-July and mid-August in 1967 

 (1965 brood year); the number of fry increased 

 from 801 to 2,084 between mid-July and mid- 

 August in 1967 (1966 brood year) (Table 16). The 

 95*% confidence interval estimates (Table 15) in- 

 dicate that the populations did increase, and the 

 additional coho salmon juveniles must have immi- 

 grated to this area from Sashin Creek. On all other 

 occasions, in both streams the populations of fry 

 and fingerlings decreased between estimates. The 

 movement of juvenile coho salmon from Sashin 

 Creek into Funny Creek during midsummer sug- 

 gests the use of this small tributary stream as a 



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