MIGRATIONS OF COD 117 
Table 46 .— Estimated ages of Nantucket Shoals cod, based on season of capture and lengths of the fish 1 
Estimated age in years 
Average length of dominant 
size group 
Estimated age iu years 
Average length of dominant 
size group 
B group 
C group 
D group 
B group 
C group 
D group 
m 
15. 1 
3 H 
23.9 
21.0 
2J4- 
19.0 
3H 
24.6 
24.4 
21.6 
2 Yi 
20.2 
4J4 
25.6 
2Vi 
21.3 
18.3 
4J4- 
24.0 
SU 
20.4 
i These data were obtained from Table 37. 
All these fish were caught in the same immediate locality (between Round Shoal 
and Rose and Crown buoys), and while the B and C cod were dominant during the 
years 1924 to 1926, the D fish were dominant during the years 1926 to 1928. This 
is perhaps the first time that observations dealing with the growth of the cod have 
been made over a period of years on the same stock of fish living in a particular 
locality, and to do this it was necessary, of course, that a good part of the population 
remain localized from one year to the next. 
That these estimated ages are approximately correct is shown by the agreement 
of the B and C groups with the growth curve, and this would seem to lend con- 
siderable weight to the correctness of the calculations. The D cod, however, suggest 
a rate of growth that is much different than that of the B or the C groups, for in effect 
the former required a year longer to reach a certain length than did either of the 
latter. Because of this, an examination of some of the scales was made in order 
definitely to locate the fish in their correct age classes. The results are given in 
Table 47. 
Table 47. — Age, according to scales, of certain groups of cod listed in Table 46 
Group 
Average 
length, 
inches 
Age 1 
Total 
number 
exam- 
ined 
Group 
Average 
length, 
inches 
Age 1 
Total 
number 
exam- 
ined 
I 
II 
III 
IV 
I 
II 
III 
IV 
B 
24. 8 
16 
16 
D 
15. 1 
49 
3 
52 
B 
25.6 
2 
11 
13 
D... 
18 3 
48 
9. 
C... 
21.3 
50 
50 
D ._ __ 
20. 4 
25 
25 
C-.- 
24.4 
1 
21 
22 
D 
24.0 
10 
45 
55 
1 The age given here represents completed years of growth. For example, the Ill-year old fish had 3 annuli on their scales and 
were in their fourth year. 
The segregation of ages given in Table 47 seems to prove conclusively that the 
distribution given in Table 46 is essentially correct, hence it appears that the D 
cod grew more slowly than the fish belonging to either of the other groups. 
The cause of this difference in the rate of growth of the D cod, as compared with 
the other two groups, is not definitely known. It was thought that perhaps they 
would exhibit some peculiarities of scale growth that would set them apart from the 
other groups, but an examination showed that the circulus count was in general 
agreement with all the other samples of southern New England cod whose scales 
have thus far been studied, for those D cod listed in Table 47 had an average of about 
21 in the first growth zone. 
