MIGRATIONS OF COD 
49 
Table 28.- — Size distribution of all the cod caught on Nantucket Shoals during tagging operations 1928 - 
1929 
Length in inches 
Per cent at each length 
1923 
1924 
1925 
1926 
1927 
1928 
1929 
0. 1 
0.6 
0. 1 
0.7 
14. 
0.1 
.4 
1.3 
0. 1 
. 1 
1.5 
0.0 
15 
.0 
1.8 
1.0 
. 1 
1.9 
.6 
16- 
. 1 
.8 
1.9 
4.3 
.3 
1.5 
2.7 
17 
.3 
.7 
1.9 
13.0 
.7 
2.2 
8.8 
18 
.5 
.4 
3.4 
17.9 
2. 1 
5.2 
10. 2 
19 
1.2 
.7 
6.6 
15.8 
6.4 
5.7 
9.4 
20 
1.7 
1.3 
8.0 
10.9 
13.3 
6.7 
7.2 
21 
2.3 
2.3 
9.0 
6.0 
17.6 
7. 1 
4.0 
22... 
2.5 
5.4 
9.6 
4.3 
15.9 
8.0 
6.2 
23 
2.6 
10.0 
5.0 
3.6 
12.1 
10.7 
8.2 
24... 
3.9 
11.4 
3.8 
4.7 
8.0 
11.6 
10.0 
25 
7.6 
12.8 
4. 1 
5.6 
5.7 
11.9 
0.0 
20 
11.6 
9.0 
5.6 
4.6 
3.7 
8.9 
5.5 
27 
13.9 
6.0 
7.0 
2.7 
2.6 
6.3 
4.3 
28 
13.4 
5.5 
7.4 
1.3 
2.6 
3.4 
4.4 
29 
12.1 
5.5 
5.8 
1.2 
2.3 
2.0 
3.7 
Length in inches 
Per cent at each length 
1923 
192-1 
1925 
1926 
1927 
1928 
1929 
30 
7.8 
5.7 
5.0 
1. 1 
1.9 
1.2 
2.8 
31 
5.0 
6.0 
3.3 
.4 
1. 1 
1.1 
1.3 
32. 
3.6 
5.3 
2.0 
.4 
.7 
.5 
2.7 
33. 
2.5 
2.8 
1.6 
.4 
.6 
.4 
.4 
34 
2.0 
2.7 
1. 2 
.4 
.5 
.3 
.6 
35 
1.6 
1.6 
1.0 
. 1 
.5 
.4 
.2 
36 
1.3 
1. 1 
.8 
. 1 
.4 
.0 
.0 
37.. 
.6 
.9 
.4 
.0 
. 1 
.3 
.3 
38. 
.6 
.2 
.6 
. 1 
. 1 
.0 
.2 
39 
.3 
. 1 
.3 
.0 
. 1 
.0 
.0 
40 
.3 
.2 
.3 
.0 
. 1 
.0 
.0 
Above 40 
.6 
.5 
.7 
.0 
. i 
.2 
.4 
Total 
100.0 
100.0 
100.0 
100.0 
99.7 
99.7 
100. 1 
Number meas- 
ured 
7, 554 
3,102 
4, 142 
1,878 
5, 712 
1,042 
704 
One point which stands out in this table is the small number of cod below 16 
inches and above 32 inches in length. The scarcity of the small fish in our catches was 
due in some degree to the selectiveness of the hook-and-line gear. However, using 
this same gear along the coast of Maine, we have caught many cod as small as 11 
inches and a few of 10 inches in length; hence it would appear that our failure to 
catch small fish on Nantucket Shoals, except at rare intervals indicates either that 
they are not present or that their feeding habits differ from cod inhabiting the more 
northern waters. The latter is not likely. With regard to the larger fish, there are 
strong indications that they tend to move into deeper water and that their scarcity 
on Nantucket Shoals is not due entirely to the local fishing. 
It will be noted that each year from 1923 to 1929 certain size groups were domi- 
nant, as, for example, the 26 to 29 inch group in 1923, the 23 to 26 inch group in 1924, 
etc. The causes for the progressive decline in the dominant sizes which occurred an- 
nually from 1923 to 1926 and the progressive increase which occurred thereafter afford 
an interesting problem. The decline appears to have been caused by the emigration of 
fish away from and the immigration of new fish to the shoals, while the increase 
resulted from the growth registered by the same school of cod which occupied the 
Nantucket grounds for at least three years. These changes will be taken up in 
detail. 
As an aid to a better understanding of the graphs and text which follow, each of 
the six outstanding schools of cod found on Nantucket Shoals from 1923 to 1929 is 
designated by a symbol ( A , B, C, D, E, or F). 
The term “stock” of fish is meant to cover the entire population inhabiting the 
region in question. “School,” “group,” “age class,” and “length class” are used 
almost synonymously to refer to one particular part of the fish population, such as the 
A group in Figure 15. In this case it is obvious that while one age class is outstanding 
among the A fish there is an overlapping of younger and older fish and the term 
“group” or “school” should not be interpreted to refer to only one age class. As 
the analysis of the length frequencies given here is made chiefly to determine the 
migrations of bodies of cod and changes in the population on the various tagging 
grounds, age and rate of growth are mentioned only when necessary as an aid in 
understanding the data. These important subjects “age” and “rate of growth” 
are discussed in a later chapter. 
