CRONE and BOND: LIFE HISTORY OF COHO SALMON 



Table 16.-Population estimates of juvenile coho salmon of brood years 1963-66' in Sashin Creek and Funny Creek in the summers of 



1964-67. Separate estimates are included for three areas of Sashin Creek. 



preceding brood year. 



^Estimate of population from expansion of estimated populations in upper area and Funny Creek. 



Table 17.-Mean stream discharge and percentage decrease in 

 numbers of juvenile coho salmon between a first estimate (late 

 June to late July) and a second estimate (mid-July to mid- 

 August) in Sashin Creek, 1964-67. 



'Stream discharge data for August 1964 not measured. An esti- 

 mate of mean stream discharge for the period was calculated 

 from July 1964 stream discharge and rainfall data in conjunction 

 with the August 1964 rainfall pattern. 



^Size of fingerling population not estimated in 1964. 



^First population estimate; second population estimate was not 

 completed. 



feeding area or refuge from undesirable condi- 

 tions in Sashin Creek, such as competition or 

 predation. Fall migration of juvenile coho salmon 

 into small tributary streams in Oregon has been 

 reported (Skeesick 1970). 



Estimates of the number of coho salmon fry and 

 fingerlings were used to construct curves depict- 



ing the changes in the sizes of the populations of 

 three of the brood years studied (Figures 10, 11). 

 Estimates of the total number of fry and 

 fingerlings in Sashin Creek in early September 

 1966 are projected from estimates of population 

 size obtained in the upper area and in Funny 

 Creek. In these two study areas in early Sep- 

 tember the number of fry averaged 60% and the 

 number of fingerlings 85% of their populations in 

 late July. We assumed that these percentages 

 pertained also to the lower and middle areas of 

 Sashin Creek. 



Survival and Instantaneous Mortality Rates 



We compared survival and instantaneous mor- 

 tality rates of juvenile coho salmon of three brood 

 years by dividing their freshwater lives into the 

 following five periods between the time of egg 

 deposition and late in the second summer of life: 



Period Time covered 



1 Egg deposition to just before emergence 

 (mid-October to late March or early 

 April). 



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