EXPERIMENTS IN TAGGING COD. 205 
the unsatisfactory use of tags made of block tin—a substance employed 
in the first year of the tagging experiments. Of over 150 tin tags 
employed, only one was recovered, and it was so much worn by the 
action of the salt water that it would undoubtedly have fallen off or 
been completely eroded within a very short time. In the case of 
copper tags, however, there is not the slightest evidence that chemical 
action was sufficiently rapid or active to cause their loss. Tags 
recovered months after attachment had undergone practically no 
change except a slight diminution in luster, their edges being as clean 
and the figures as sharp as when first put in the water; and in no 
instances was there observable any general or irregular thinning of 
the copper wire by which the tags were made fast. 
While it is probable that some tags have been lost by the gradual 
tearing of that part of the fin through which the wire passed, the 
available evidence fails to show that many tags could have been lost 
in this way. A considerable number of tags have been returned to 
the Commission either with the entire fish or with the fins to which 
they were attached. In none of these cases has there been any indica- 
tion that the tag was in danger of being lost through tearing of the fin. 
Sometimes the fin was entirely healed around the wire, and sometimes 
a small slit in the interradial tissue had been formed by the movement 
of the tag. Very exceptionally a raw surface existed around the wire, 
and the fishermen occasionally reported that the wire had made a 
small sore in the fin. 
It is clearly evident that the explanation of the point under consider- 
ation lies not in the tags but with the fish themselves, although what 
the real explanation is can only be surmised. 
Mention has been made of the curious absence of tagged fish from 
the Nantucket Shoals in fall and winter, at a time when very active 
fishing is going on, and when the tagged fish were originally caught on 
these same grounds. It is possible that when the Nantucket Shoals 
cod have attained a certain age they cease to resort there, at least in 
fall and winter, and seek other grounds at that season, perhaps going 
to the offshore banks, where, becoming more widely dispersed and 
mixing with a larger body of fish, they are less likely to be caught than 
in the shore waters. This supposition carries with it the suggestion 
that the cod frequenting the Nantucket Shoals each fall and winter go 
there for the purpose of spawning, and represent new schools of fish 
that have perhaps come in from the offshore grounds. 
The data on which to base deductions are obviously too meager. 
THE LARGE PERCENTAGE OF TAGGED FISH CAUGHT. 
The fact that about 4 per cent of the fish tagged and released were 
subsequently captured by the commercial fishermen raises several impor- 
tant questions. It must be conceded that this is an unexpectedly large 
proportion, when the abundance of cod on our shores and the wide 
