118 
BULLETIN OF THE BUREAU OF FISHERIES 
It would be natural to look to the scales of the 15.1 -inch D cod as a means of 
ascertaining the early growth of this group of fish. (Table 46.) But this may have 
given an erroneous result, because these fish centering around 15 inches were probably 
the largest individuals of their class on account of the selectiveness of hook-and-line 
gear. However, lengths calculated from the scales of older fish showed that at the 
completion of the first growth zone the C cod were 8.1 inches long, while the D cod 
were but 6.3 inches, and that therefore much of the 3-inch difference in size between 
the C and the D cod at 2% years of age had already been made early in the life of the 
fish. 
It was considered that the D cod possibly were genetically or inherently a slow- 
growing group. Such might be the case if they originated from eggs spawned in 
northern waters where cod presumably grow more slowly than they do to the south- 
ward. It is possible that under unusual circumstances the larvae and fry from such 
eggs might reach the Nantucket region, but that this happened in the present instance 
is not likely. It is more probable that the difference in growth was due to unusually 
favorable conditions which may have obtained during 1 923 when the C cod hatched 
as compared with 1924 when the D brood originated. 
These various growth and age determinations might be summed up as follows: 
1. Length frequencies obtained from time to time from what were presumably 
the same stocks of fish indicate that on Nantucket Shoals cod 15 to 26 inches long 
increase in length about 2j/£ to 4 inches a year. 
2. Recaptures of tagged Nantucket Shoals cod have shown that fish 17 to 24 
inches long grow about 4 inches a year, while fish 25 to 35 inches long grow about 
2 y<i inches a year, the smaller fish in each of their length groups and those in the 
preceding paragraph showing a somewhat greater increment than the larger. 
3. Giowth was somewhat faster during the summer than from fall to spring. 
Table 48 .—Age with respect to size 
i 
II 
III 
IV 
V 
Estimated from length-frequency distributions 
Calculated size, according to scale growth 
Size. according to acre determinations from scales 
Inches 
7-8 
7 
Inches 
14-16 
15 
16-17 
Inches 
19-22 
21 
22 
Inches 
23-25 
25 
25-26 
Inches 
27- 2 
28- 2', 
i 
RESUME OF CONCLUSIONS 
1. Cod are to be found on Nantucket Shoals throughout the year, but are most 
abundant there from spring to fall. 
2. The stock of cod living on Nantucket Shoals, consisting chiefly of young 
adult and nearly adult fish, is for the most part distinct from that living to the 
north and east of southern Massachusetts, for there is no general intermingling of 
the fish belonging to these regions. This conclusion is supported by the recapture 
records of tagged fish and by scale studies. According to the first named, only a 
very small percentage of the Nantucket cod stray to the north and east annually, 
and, conversely, only a few cod tagged to the north and east stray to Nantucket 
Shoals. 
3. A large part of the Nantucket Shoals cod population make a fall migration 
into the Rhode Island-North Carolina region, where most of them remain until the 
spring. These fish are joined by others from the north and east of Cape Cod; but 
