THE SPEED OF MIGRATION OF SALMON 
589 
Fig. 2 Photograph showing the obverse faces of the aluminum buttons pictured 
in fig. 1 The order of arrangement is the same in the two pictures. 
marking buttons that were extensively corroded. These fish made 
the entire journey at an average speed of from 6.36 to 7.50 miles 
per day. On the basis of the evidence that corrosion furnishes, 
these individuals must have spent some time in brackish or salt 
water. 
Silver salmon numbers 79 and 75 bore buttons that were in the 
first case not corroded, and in the second only slightly corroded 
on one side. From the line of evidence which has been given con- 
sideration one must infer that these fish did not spend much time 
at or below the point where they were liberated. 
Silver salmon number 87 is a decided exception in the list. This 
fish was re-taken only seventy miles up the river, yet it was out 
a total of fifty-seven days. The marking button does not present 
evidence of long contact with sea-water. It is slightly corroded 
on one surface but not more than would occur in slightly brackish 
water. 
