SALMON OF THE YUKON RIVER. 



3 2 3 



The following table (3) gives the average sizes attained by the different year classes 

 in the two years 1919 and 1920, the males and females being stated separately. In 

 comparing these with similar averages obtained in other districts, we must bear in mind 

 that our Yukon material shows no growth belonging to the season in which the fish were 

 captured. Our 4-year individuals had completed three years of growth, but no more, 

 and similarly with each of the other year groups. However, no strict comparison is 

 possible between Yukon 4-year fish and the 3-year fish from other localities, for although 

 the latter had produced a certain amount of new growth in their third year, they had 

 not completed the growth of the third year when they ceased feeding and were cap- 

 tured. In like manner no exact correspondence can be expected between 5-year 

 Yukon individuals and 4-year material from the Columbia or the Fraser. In com- 

 paring growth rates from these different localities, the most satisfactory basis will be 

 found in completed lengths of the different year classes, computed from the scales. 

 By length is meant the distance, measured over the curve of the body, from tip of snout 

 to distal end of middle caudal rays. 



Table 3. — Average Lengths tor Certain Year Grow 01 Vi kon King Salmon. 1920 and 1919. 



Sex and year. 



3-year croup. 



4-year group. 



Average 

 length. 



Number. 



Average 

 length. 



5-year group. 



Number. 



Average 

 length. 



6-year group. 



»«*«■ ffl* 



7-year group. 



Number. 



Average 



length. 



Males: 



1920. . 

 1919. . 

 Females: 

 1920. . 

 1919. . 



Inches. 

 16 



Inches. 



23.4 

 26.3 



119 

 16 



Inches. 



313 

 31 



33-5 

 3S-6 



106 



15 



Indus. 

 38.7 

 37-5 



36 



Inches. 

 41-8 



4i- ; 



40. 1 



37-7 



For comparison with other regions we have calculated the growth for each year of 

 their lives of jj fish belonging to the fourth, fifth, sixth, and seventh year classes and 

 present the results in Table 4. We have followed Fraser's latest paper 2 in taking 1.5 inches 

 (40 mm.) as the average length of the fry when the first scale ring was formed. Several 

 differences are encountered in comparing our results with Fraser's. His material was 

 largely taken in the Gulf of Georgia and included a mixture of fish that would mature 

 during the then current season with others that would delay maturing for one or more 

 years; also, doubtless, a mixture of races, bound for different river basins and unlike in 

 certain of their characteristics. His measurements are throughout smaller than by our 

 method, inasmuch as they do not include the length of the middle caudal rays. 



Table 4, which follows, shows with regard to each year class that the growth during 

 the year that precedes maturity is greater than during the corresponding year of classes 

 that reach a greater age. Thus the third year's growth of fish that mature in their fourth 

 vear is greater than the third year's growth in fish that would not mature until their fifth, 

 sixth, or seventh years. Furthermore, it is greater in 5 than in 6 year fish and greater 

 in individuals that mature in their sixth than in those that mature in their seventh year. 

 The third-year growths form a regularly ascending series from j.$ inches in the oldest 

 year class to 12.4 inches in the youngest, and the lengths of the fish at the end of their 

 third year form a similar advancing series. According to this table we should find 

 that the largest series of 3-year fish hi the sea at any time is composed of those indi- 

 viduals that will earliest mature. The same is true of the growth of the fourth year 



2 Further Studies on the Growth Rate in Pacific Salmon, by C. M. Fraser. Contributions to Canadian Biology, 1918- 

 1920, pp. 7-27. Ottawa, 1921. 



