326 BULLETIN OF THE BUREAU OF FISHERIES. 



checked until the end of the season, but, strangely, during the second week in July a 

 fresh run of chums that was no further advanced than were the ehums of early June 

 made its appearance. These also were of bright silvery color and had symmetrical 

 jaws and abundant oil. Although entering relatively late, it seems safe to assume that 

 this run was far from its spawning period and had far to go. Along all the lower and 

 middle portions of the river fishermen who prepare dried salmon for winter use dis- 

 tinguish between the silvery chums and the others. The "silvers" have flesh of brighter 

 color, rich in oil, and of more substance when dried. The others are known as "dog 

 salmon," with intermediate stages called "half-breeds," and are far inferior in value for 

 human consumption or as dog feed. 



The Yukon chums in their prime are doubtless of far higher quality than chums 

 from any other river. The differences between them and other races of chums are of 

 similar nature to those that distinguish the Fraser River sockeyes from the same species 

 known as red salmon in the average Alaska streams and to those that distinguish the chinook 

 salmon of the Columbia from the same species ("king salmon") in the shorter streams of 

 the north. The differences in all these cases are not only of similar nature, they are due 

 to the same cause. The fine quality of Yukon chums, Fraser sockeyes, and Columbia 

 chinooks is due to the great length of stream which they must traverse, while fasting, on 

 the way to their spawning grounds and to the large store of oil that they must lay up 

 for use at this time. In no other respects are the chum salmon of the Yukon different 

 from the same species found elsewhere. The Yukon king salmon, as we have previously 

 noted, are characterized by the same excessive provision of oil. They also exhibit in the 

 different portions of the run equally striking differences between bright individuals, 

 relatively green as to eggs and milt, and the sexually advanced forms, with hooked 

 jaws and discolored skin. It would be no less logical to recognize two or three kinds of 

 king salmon than it is to distinguish, as is popularly done on the Yukon, two or three 

 kinds of chums, according to the degree of their advancement toward spawning. 



RATE OF TRAVEL. 



The chum salmon is generally known as a species that spawns exclusively in the 

 lower courses of streams, often scarcely above the reach of the tides and never far from 

 salt water. It is a remarkable reversal of habit in the Yukon chums that colonies of 

 them should penetrate more than 2,000 miles to the upper tributaries of that great river; 

 and it testifies to the flexibility of organization in salmon that a species that is in general 

 not adapted to long journeys while fasting, can, under spur of necessity, make such journeys 

 without food and exhibit great speed and endurance. From records of the first appear- 

 ance of chums at a large number of stations during the season of 1920, it was apparent 

 that their rate of travel was not far below that of the powerful king salmon. They 

 entered the river about a week later than the kings, at Tanana they were not more than 

 10 days behind the latter, and at Dawson they were some 14 days behind the kings. 

 The lower 800 miles of the river, as far as Tanana, were traversed at the rate of 50 miles 

 per day, and the next 700 miles, between Tanana and Dawson, were covered at the rate 

 of 35 miles per day. The lower 1,500 miles were ascended at the rate of 42 miles per 

 day. 



YEAR CLASSES. 



We have already noted that the king salmon of the Yukon are retarded in their 

 development and mature on the average more than one year later than the king salmon 



