8 U. S. BUREAU OF FISHERIES. 
stantial runs in the Yukon River (king, chum, and coho), and of 
these king and chum are of the greatest importance by far. The 
few reds or sockeyes taken near the mouth of the river are perhaps 
strays, for no breeding has yet» been reported from any part of the 
Yukon Basin. Humpbacks appear at the mouth of the river more 
numerously than the red salmon, but never in sufficient numbers to 
constitute a run even of small dimensions. As they were far ad- 
vanced toward spawning in July, it was evidently impossible that 
they could ascend the river far with their spawning period so close 
at hand. ‘The coho runs more or less numerously than the king or 
chum salmon and in addition is the latest to appear, often not pre- 
senting itself in any numbers in the middle and upper reaches of 
the river until the ice is forming in the fall. 
The king salmon begins running in the last week of May or the 
early days of June. The run culminates quickly and then almost as 
quickly deelines. The rate of migration was found to be remarkably 
high, the average rate of travel from Tanana to Dawson being 
slightly less than 45 miles per day, and from Pilot station to Daw- 
son, involving practically the entire length of the river below Daw- 
son, the average rate was 57 miles per day. No record of any other 
river approaches this in completeness, nor in the high rate of travel 
indicated. . This unexampled speed with which salmon ascend the 
Yukon is doubtless associated with the great distances to be traversed 
before reaching their upper spawning areas, taken in connection with 
the shortness of the summer season. 
The most important natural enemies of the king salmon are the 
white whales, or belugas, and the lamprey eels, the former being 
undoubtedly exceedingly destructive, while the latter, though caus- 
ing scars on the fish in much greater abundance than in any other 
river, as observed by investigators, do not appear to effect serious 
injury to the fish. 
The chum salmon, which is the principal food product of the 
Yukon River, made its appearance but a few days later than the 
advent of the king salmon, the rate of migration being approxi- 
mately the same as that of the king. 
Two phases in the development of the chum salmon are distin- 
guished by the natives under the names of “ dog salmon ” and “ silver 
salmon,” the deg salmon comprising the individuals furthest ad- 
vanced toward spawning. In general the “dog salmon” along any 
stretch of the river consist of those individuals which will turn into 
some adjacent tributary to spawn, while the “ silvers” are on their 
way to the upper reaches of the river, show relatively little of the 
sexual changes they will exhibit on their spawning beds, and are 
still richly provided with the oil which serves as fuel and the princi- 
pal source of nourishment during the long journey still before them. 
“ Dogs” and “silvers” were in general keeping apart from each 
other and following distinct migration routes, the “dogs” pre- 
dominating on the right and the “silvers” on the left side of the 
stream. Heavier runs of kings and cohos were found in company 
with the “silvers” along the left limit of the river. It appears, 
therefore, that there is a prevailing use of the left shore by those fish 
which are found in the upper reaches of the river. This may have 
