SALMON OF THE YUKON RIVER. 



327 



from southern waters. A similar retardation is observed in chum salmon, which aver- 

 age distinctly older in the Yukon than in any other region of which we have record. 



The earliest report on the ages attained by this species and on the relative propor- 

 tions of the year classes was based on a small collection taken at Bellingham, Wash., 

 early in August, 1910. 3 The number investigated was too small (58 in all) to give 

 reliable averages, but the percentages indicated do not differ materially from those 

 obtained in 19 16 by Dr. C. M. Fraser from collections of adequate size taken at Nanaimo 

 and Qualicum, in the Gulf of Georgia. In both cases the majority of the chums were 

 found maturing at the age of 3 and 4 years, with very few individuals at 5 years and an 

 occasional rare specimen in its second year. Table 7 gives the results derived from 

 both sources and also, for comparison, includes a similar grouping of Yukon chums. 



Table 7. — Year-Class Distribution, Southern and Yukon Chum Salmon. 



The Yukon chums mature in their third, fourth, and fifth years, as is the case in more 

 southern waters, but the number of 3-year-olds is diminished from nearly half to one- 

 thirtieth of the total number, and the 5-year fish show a corresponding increase from 1 

 to nearly 30 per cent. The retardation in the maturing of the northern race is thus 

 evident. 



PROPORTIONS OF SEXES. 



It has commonly been reported that dog-salmon males are greatly in excess of the 

 females, but no thoroughly satisfactory investigation of this subject has been made. To 

 accomplish this, an examination would have to be made of the ratio of males to females 

 at frequent intervals throughout an entire run. It might well be expected that the 

 proportions of the sexes would differ widely during consecutive portions of the run, 

 with the result that any deficiency in the number of females observed at the beginning of 

 the run would be compensated for by an excess of females later on. Such an occur- 

 rence has been repeatedly observed in certain sockeye colonies. Four-year male sock- 

 eyes entering Rivers Inlet, British Columbia, in 1917, varied from 100 per cent of the 

 4-year class in early July to 52 per cent on July 31 ; and the 5-year males varied from 59 

 per cent of the 5-year group ou July 10 to 23 per cent on July 31. It is clear, therefore, 

 that a scries of observations on fish bound for one river only will be necessary to enable 

 us to determine this point. 



Doctor Fraser's results, from fish taken partly near the mouth of the Little Qualicum 

 River and partly from the vicinity of Nanaimo, agree in showing from both dis- 

 tricts an increased percentage of males in the older year classes. The percentages of 

 males in the third, fourth, and fifth year classes in the Nanaimo lot, range 42.6, 62.1, and 

 100; in the Qualicum lot, 51, 63.8, and 86.4. If these represented the average percentages 



3 Age at Maturity of the Pacific Coast Salmon of the Genus Oncorhynchus, by Charles H. Gilbert. Bulletin. U. S. Bureau 

 of Fisheries, Vol. XXXtl. 1912 (1914), p. 18. Washington, 1913. 



