33° BULLETIN OF THE BUREAU OF FISHERIES. 



which they are exposed. Growth during the seaward migration can not be considerable, 

 for none of the material that we have examined indicates the formation of the scale 

 nucleus while still in the stream. 



Growth of this species in the sea seems to proceed with remarkable regularity, with 

 the result that the scales are diagrammatic in their simplicity and seldom afford any 

 difficulty in determination of age. In the case of the Yukon race, such uncertainty as 

 may be experienced is concerned with the interpretation of the peripheral region of the 

 scale and is based on the fact that the scale margins differ widely in condition among 

 individuals captured on the same date. It is generally recognized that individuals of a 

 given race will vary materially in the date on which they begin the rapid growth of the 

 spring after the winter pause. Among the fish captured in May or early June in more 

 southerly waters an occasional individual may indicate no growth of the current season, 

 while others will vary in the number of peripheral wide rings by which the amount of 

 spring growth may be computed. In the Yukon dog salmon, however, this variation 

 at the time they leave their feeding grounds and enter on their spawning run is extreme. 

 An occasional fish, as shown by Figure 296, had begun no new growth of the year, the 

 margin of the scale being formed by the close-ringed check of the previous winter. 

 Others, as represented in Figure 294, had barely inaugurated the new growth, which is 

 indicated by two or three wide rings outside the winter check. There then follow fairly 

 complete series with ever-increasing growth of the season, as shown in Figures 297; 

 290, 291, and 292, the last named having finished an average season's growth for the 

 third year, with the exception of the winter check. 



When it is recalled that these dog salmon enter the Yukon in company with the 

 king salmon and that the king salmon have not in any case made unmistakable growth 

 for the current season, the habit of the dog salmon in this regard seems most peculiar. 

 In the early and middle parts of the run, to which alone we had access, none of the 

 individuals examined had begun a winter check at the margin of the scales for the cur- 

 rent year. Where a marginal winter check existed, it had been formed the previous 

 winter and presented no real difficulty in determining age. If the latter part of the 

 run should be found to contain a group of individuals in which a check was forming 

 at the scale margin and also another group with scales like Figure 293, in which the 

 marginal check belonged to the previous winter and no further growth had been regis- 

 tered, a real difficulty might arise in determining the age of such individuals. The 

 two groups would show essentially similar scale structure, but one would be one year 

 older than the other. It is not probable, however, that representatives of these two 

 classes would be found together in any portion of the run. As the season advanced we 

 should expect to find extremely few, if any, that had failed to produce some new 

 growth of the year. 



THE SOCKEYE SALMON (Oncorhynchus nerka). 



A few scattering sockeyes (Alaska red salmon) enter the Yukon River during 

 July and early August. In 1919 the Carlisle Packing Co. put up 22 cases of tails and 

 6 cases of flats of this species and handled a total of about 300 fish. The sockeyes 

 appeared even less numerous in the following year, when only 5 cases, containing about 

 60 fish, were packed. 



If a permanent colony of red salmon exists in the Yukon, it must ascend to the 

 lakes near the source of the river, but we have no knowledge that such spawning grounds 

 for this species exist. That individuals ascend the river for long distances is certain, 



