MIGRATIONS OF COR 
13 
may be classed as follows: (1) The tail may be entirely healed with the tag securely 
attached; (2) the tail may be healed but the tag retained by only a small piece of 
skin and flesh; (3) suppuration may have set in, although the tag is still secure; (4) 
suppuration may have set in and the tag is on the point of dropping off ; and (5) a 
wound or scar may be left where the tag has eaten its way out of the tail. 
We have insufficient data upon which to determine what percentage of the fish 
fall into each of these categories a year after tagging, but by far the greater part of 
them belong to the fifth class, as they have lost their tags. 
The loss of tags may be caused by insecure attachment in the first place, as in 
the case of small fish, or by becoming movable because of softened tissue about the 
point where it penetrates the flesh. There is perhaps some friction as the tag passes 
through the water, and the swimming movements of the fish itself may assist in dis- 
lodging a loosely attached tag. Sometimes barnacles, hydroids, etc., attach them- 
selves to the tag and probably aid in its loss. 
Some idea of the percentage of cod that lose their tags was obtained from the 
marked fish that were recaptured by the Halcyon and the Albatross II. A comparison 
of the number of tag-scarred fish with the number of recaptured tag-bearing cod that 
had been marked at least the year previous gave the following result: In 1924 out of 
22 marked cod which fell in this category 15 bore tags and 7 had tag scars; m 1925 
out of 12 fish, 6 had tags and 6 had tag scars; in 1926 out of 10 fish, 3 had tags and 7 
had tag scars; in 1927 out of 36 cod, 8 had tags and 28 had tag scars; in 1928 out 
of 18 fish, 8 had tags and 10 had tag scars; in 1929 out of 7 fish, 2 had tags and 5 
had tag scars. The total of our own recaptures, therefore, of cod with tags attached 
that had been at liberty at least from one year to the next numbered 42 and those 
with tag scars numbered 63. 
All the foregoing fish were tagged and recaptured on Nantucket Shoals and most 
of them were tagged and reexamined upon recapture by the same person, so it is 
difficult to see how the fluctuations in the loss of tags from year to year could be 
due to differences hi the technique of tagging that would result if more than one 
person were involved. While the rate of loss of tags from the tail may diminish 
once the healing has been accomplished, nevertheless our records show that after the 
fish have been at liberty as long as three and one-half years only about 1 out of 10,000 
is recaptured with its tag intact. 
In 1927 an attempt was made to reduce the loss of tags and so some of the fish 
were tagged on the lower jaw. Although it seemed impossible for the tag to become 
dislodged from its place of attachment, yet the percentage of returns from the fish 
so tagged has not shown sufficient improvement to justify the discontinuance of the 
tail-marking method. 
Intensity of fishing as affecting the tag returns. — The intensity of fishing on the 
tagging grounds and in localities to which the fish migrate has a direct bearing on 
the proportion of the marked fish which are reported recaptured. Unfortunately, 
the data available are too incomplete to show what degree of correlation might exist 
in this respect. Mention is made in several parts of this report of the catch of cod 
taken on Nantucket Shoals and in other regions to which these cod migrate. 
The percentage of recaptured fish which are not reported. — Although the tags of 
some recaptured fish are lost due to various causes, it can be said with assurance 
that by far the greater part of those obtained by fishermen are reported. 
