56 
BULLETIN OF THE BUREAU OF FISHERIES 
direction. A new school of cod, D, appeared at Round Shoal buoy in August, 1925, 
and the sizes of its individuals formed a small peak at 14 inches. If these small cod 
had passed out of the picture by October they would scarcely deserve passing men- 
tion, but it happened that they were the forerunners of the most dominant group 
of cod, including the largest number of individuals, of any school found on Nantucket 
Shoals during the years 1923-1929. There were, then, three distinct schools of fish 
on the Round Shoal buoy grounds — the dominant C school, the B school of secondary 
importance and fading out of the picture, and the D school just forming and destined 
to become the greatest of all within the next two years. 
The first fishing on the Great Rip grounds in 1925 was not started until Aug- 
ust. Unfortunately, no cod were tagged there during 1924, so that we have fewer data 
to compare than for the Round Shoal-Rose and Crown region. We found, however, 
that the C cod were of secondary importance, the B cod were dominant, and the D 
cod had not yet appeared. (Fig. 18, No. 2.) 
It will be noted that the length frequencies of the B and the C cod at Great Rip 
do not coincide with those of Round Shoal buoy, and the question might justly arise 
as to whether too much dependence is being placed on the length frequencies alone 
as a means of identifying these schools of fish. While the B cod differ very little, the 
peak of the Great Rip C cod lies between 21 and 22 inches instead of between 20 and 
21 inches, as at Round Shoal. A similar situation was found to exist in 1926, when 
18-inch cod were present at Round Shoal and 20-incli cod at Great Rip (fig. 19), but 
an analysis of scale samples of these fish showed that the difference in length was 
caused by an increase in the rate of growth due probably to a more abundant food 
supply at Great Rip rather than to a difference in age (p. 58). 
During October, 1925, two cruises were made to Nantucket Shoals, the first 
from the 1st to the 6th and the second from the 24th to the 30th. On each of these 
cruises fishing was restricted to the Round Shoal to Rose and Crown grounds. 
Although we could have reasonably expected some differences between the length- 
frequency distribution of the late October fish as compared with that of the fish taken 
earlier in the month, due to emigrations and immigrations which are apt to occur at 
that time, the lengths were very much the same on both cruises; hence, they have 
been combined in Figure 17, No. 4. There were, however, somewhat fewer cod 
present late in October, for whereas a catch of 40 fish per hour per unit of effort was 
made early in the month only 30 fish per hour were taken the end of the month. This 
indicated that some of the cod had already started westward by October 24. If 
cod from east or north of Nantucket Shoals were migrating westward by the end of 
October there were not enough of them on the Round Shoal grounds at the end of 
October to materially affect the length-frequency distribution which had obtained 
since the preceding August. A comparison of Figure 17, No. 3, with Figure 17, No. 4, 
will show how remarkably stable the stock of fish was from summer to fall. 
The year 1925 may be summed up as follows: 
On the Round Shoal to Rose and Crown grounds the stock of cod was so much 
the same from month to month that there can be no question but what the major 
part of the fish, as we found them on our first cruise in May, remained in the imme- 
diate vicinity of these tagging grounds throughout the spring, summer, and fall. 
Briefly, the outstanding features of this stock of fish were that the C cod remained 
predominant throughout the period from May to October; the B cod, although 
present at all times, consistently declined in dominance from May to October; and, 
