ABSTRACT 



Early maturing fish that have spent only one year in the ocean are common in the 

 spawning escapements of Columbia River blueback salmon (Oncorhynchus nerka), 

 particularly in the Okanogan tributary. The unusually high incidence of these 1-year- 

 ocean fish in 1953, however, led to a study to determine the average fecundity of the 

 ocean-age groups composing the runs, and to assess the effect of varying age and sex 

 composition on estimates of reproductive potential. 



A fecundity stvidy in 1957-59 revealed that the average egg content of 1-year- 

 ocean females was approximately one-third less than that of 2-year-ocean females. 

 The average egg content of 3-year-ocean females was, in turn, about one-fourth greater 

 than that of 2-year-ocean females. 



Analysis of the age group fecundity and sex ratio data showed that the number 

 of spawners or even female spawners does not always accurately portray the repro- 

 ductive potential of an escapement. Erroneous reproduction estimates seriously 

 distort escapement-return relationships. 



