MIGRATIONS OF COD 
45 
of the best fishing grounds. The large catch made in May, 1927, was due to the 
presence near Round Shoal buoy — one of our chief tagging grounds — of a dense school 
of medium-sized cod. They probably extended over a large part of Nantucket 
shoals, for cod were more plentiful on all of our tagging grounds off Nantucket 
during 1927 than during any of the other years. 
The wide fluctuations in the October catch are of interest because it is during this 
month that the westward migration commences. Thus it would seem that in October, 
1924, a large part of the fish had already started westward at the time we fished the 
shoals. In October, 1928, this was still more apparent, for although during the 
early and middle parts of the month there occurred one of the best catches of cod on 
the shoals ever made by commercial vessels (Table 24, p. 44), fish were relatively 
scarce at the time we fished there during the end of the month. 
While we can not be sure that the results obtained on the tagging grounds hold for 
all of Nantucket Shoals, it is very likely that they represent the conditions over a 
large part. Numerical data dealing with the catch of fish per unit of effort should 
always be interpreted broadly, because chance is always an important factor in the 
finding of fish, especially when only one vessel is operating, and some variation in the 
catch would occur from this cause alone even though the stock of fish remained 
virtually the same as to numbers from month to month or from year to year. 
Other evidence that cod remain localized on Nantucket Shoals for an extended 
period is shown by the time sequence and. the tag-number sequence of the recaptures, 
for it was noted that many of the marked fish were retaken in almost identically the 
same place where they had been tagged and that often when one fish was recaught 
others woidd follow soon after as long as we fished the same ground. 
Thus the Halcyon recaptured 6 cod on August 20, 1925, at Round Shoal buoy by 
drifting repeatedly over a small spot about one-half mile long during two and one-lialf 
hours of actual fishing. These recaptures were taken at the following minutes of the 
day: 3, 3.15, 3.25, 3.35, 3.40, and 4.10 p. m. Five of these fish had been tagged at 
Round Shoal buoy the previous May and June. In contrast to this we fished 20 miles 
to the southward, around Great Rip, from August 23 to 25, for 18 hours, and caught 
about 1,000 cod, among which there was not one tagged fish. The reason for this was 
apparent, for we had not tagged any cod at Great Rip since 1923, whereas several 
thousands of fish had been tagged around Round Shoal buoy between October, 1923, 
and June, 1925; hence the good return of tagged fish which we obtained there in 
August, 1925. Not only does this show that a large part of the fish remained on the 
shoals but that they did not move far from the immediate vicinity of the tagging- 
grounds, else we probably would have caught some of them around Great Rip. 
Another case of this sort occurred at Round Shoal buoy on October 3, 1925, 
when seven hours’ actual fishing was done there and 6 tagged cod were recaptured by 
the Halcyon, as follows: 8.20, 8.30, 10.40, 10.45, 10.50 a. m., and 1.30 p. m. All these 
fish had been tagged at Round Shoal buoy between April, 1924, and August, 1925, on 
four different cruises. 
Other instances of this kind were found not only on Nantucket Shoals but on 
other grounds in the Gulf of Maine as well. Off the coast of Maine in particular, where 
we have tagged and recaptured many cod close to shore, and thus could take precise 
bearings on our tagging localities, there were many instances where tagged fish were 
recaught in rapid succession and often of nearly consecutive number. There is a good 
example of this off Petit Manan, east of Mount Desert, Me., where on July 13, 1925, 
