THE SPEED OF MIGRATION OF SALMON 
583 
aluminum is light and furnishes sufficient surface for the stamping 
of numbers, initials, or other matters of identification. The tag 
was made of two pieces on the general principle of a Yankee but- 
ton. The first piece consisted of a circular disc forged on to a 
hollow shaft some 7 mm. in diameter. The disc of this piece had 
a serial number stamped upon it. The second piece was similar 
to the first except that the disc was forged on a solid rod or rivet. 
The disc of this piece carried the legend ''U. S. Fish." When the 
rivet of the second piece was inserted into the shaft of the first 
piece and compressed, the aluminum filled the cavity so as to 
make it impossible to separate the two. 
THE DETAILS OF THE MARKING 
The salmon is a gamey fish. When taken in a dip net it strug- 
gles violently to escape. By skillful management a salmon can 
be held just under the surface of the water in such a way that its 
struggles will produce marked fatigue. When a fish is thus fa- 
tigued it will remain quiet for some seconds. In this work advan- 
tage was taken of that fact and the instant the salmon stopped 
struggling it was lifted out of the water, grasped by the base of the 
tail, swung free of the net, and laid gently on the measuring board. 
In this position the tip of the nose was brought up against the 
vertical end of the measuring apparatus, and the length read off 
and announced to the recorder. The next step was to attach 
the marking button. This was done by puncturing a hole in the 
caudal fin into which the button was inserted and riveted. The 
whole process required less time than it takes to describe it. 
The salmon stood the handling very well. They were immedi- 
ately released overboard in the direction of open water. If there 
was the slightest question as to asphyxia, the fishes were first 
released back into the car and later, when they had fully recovered, 
were turned into open water. The fishes of this series came 
through in exceptionally good condition. 
