456 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



includes both the within- and the between-rivers 

 regressions. The within- and the between-rivers 

 regressions each has a useful connotation. If 

 one wishes to estimate from the lengths of the fish, 

 the number of eggs contained in a sample of chum 

 salmon from a particular river, then from the 

 between-rivers regression one obtains an estimate 

 of the average number of eggs per female (left 

 ovary) in accordance with the average length of 

 the entire sample. If, however, one wishes to 

 determine the difference in egg number (left ovary) 

 between fish of different lengths within the same 

 sample, then the slope of the regression would 

 follow the within-rivers slope. 



RELATION OF AGE AT MATURITY TO 

 NUMBER OF EGGS 



The best material available on the effect of age 

 at maturity on egg count is in unpublished data 

 for the sockeye salmon of Karluk River, Alaska, 

 as follows : 



* Left and right ovaries estimated separately. 



2 Summary published in Gilbert and Rich (1927). 



Some measure of the reliability of these data is 

 contained in figure 4, which sliows for 1938 the 

 average weight in grams for 1 egg of the right 

 ovary plotted against the weight of 1 egg of the 

 left ovary for 41 Karluk River sockeye of ages Sg, 

 63, and 64. The samples were taken from salmo'i 

 captured at the mouth of the river so that there is 

 great variation in the stage of maturity of the ova, 

 but the figure shows that the eggs in the two 

 ovaries are maturing at the same rate. Since the 

 data from the two ovaries form two independent 

 estimates from the same fish, their close agreement 

 gives confidence in the consistency of this method 

 of calculating the number of eggs. 



to 



.02 ,03 .04 .05 .06 .07 .08 .09 JO ,11 ,12 



V/EIGHT IN GRAMS OF ONE EGG- LEFT OVARY 



Figure 4. — Paired observations of egg weights in right and 

 left ovaries of sockeye salmon, 0. nerka, of ages Bi, 63, 

 and 64, of Karluk River in 1938. 



It is interesting to note that although the eggs 

 in the left and right ovaries maintain the same rate 

 of egg maturation the total number of eggs in 

 the two differ noticeably. Figure 5 shows that 

 for low total number of eggs the right ovary 

 contains as many eggs as the left or more; 

 however, as the total number of eggs rises the 

 proportion in the left ovary becomes increasingly 

 greater than in the right. 



Kendall (1921, pp. 195, 197) says. 



As the ova approach maturity, the left ovary is nearly 

 or quite always the longer, and it extends, tapering, to the 

 posterior end of the abdominal cavity. 



600 800 1000 1200 1400 1600 I BOO 2000 2200 2400 2600 

 NUMBER OF EGGS IN LEFT OVARY 



Figure 5. — Relation between the egg number in the right 

 and the left ovaries of the sockeye, 0. nerka, of Karluk 

 River in 1939. 



