MIGRATIONS OF COD 109 
Table 40. — The number of circuli formed on the scales of Nantucket Shoals cod within the first zone of 
growth ( presumably the first year's growth), segregated according to the size of the fish 
Length of fish, inches 
Number of 
fish 
Average 
number of 
circuli in 
first zone 
of growth 
Length of fish, inches 
Number of 
fish 
Average 
number of 
circuli in 
first zone 
of growth 
20 
22.0 
31 
17 
19.9 
21 
4 
18.5 
32.. 
17 
18.8 
22 ___ 
11 
20.4 
33 
2 
18. 0 
23 
12 
19.0 
34 
5 
21.2 
24 
19 
20.3 
35_ 
5 
21. 6 
25 
35 
19.7 
36_ 
8 
18.9 
26 
66 
19.7 
37 
27 
79 
20. 1 
38 
4 
19.0 
28 
63 
20 8 
29 . 
55 
20.9 
Total 
438 
20. 2 
30. 
30 
20.7 
As the scales of this sample of adult Nantucket Shoals cod had an average of 
about 20 circuli in the first growth zone of their scales, or about the same number as 
the 156 to 197 millimeters yearling cod just mentioned, it is evident that approxi- 
mately this number is formed when the fish have completed their first year. Therefore 
when the first growth zone contains relatively few circuli, say 10 to 15, it is apparent 
that these represent less than one year’s growth, and when the number is large, say 
over 25, it is probable that they are the result of more than one year’s growth. 
One striking result brought out by the tabulation given in Table 40 is that the 
average number of circuli in the first growth zone on the scale is about the same, 
regardless of whether the fish were as small as 22 or 24 inches long or whether they 
were as large as 36 or 38. This is as it should be if we are to believe that cod do not 
shed their scales but retain them from the time they first form, throughout their 
lifetime. Regenerated scales which take the place of those which are lost (through 
injury) can always be easily detected by a central area without circuli, which often 
takes up about one-half of the entire scale. Creaser (1926) and Van Oosten (1929) 
have established experimentally the correctness of this interpretation of these central 
areas devoid of circuli. 
Segregation of cod stocks as shown by scale structure .- — Perhaps the greatest value 
to be obtained from a study of the first-zone circuli is the light which it throws on the 
origin and migrations of the cod, for it seems apparent that if the growth of the scales 
from two separated grounds should differ, then no general intermingling of the cod 
dwelling in the two regions in question will have occurred. The fact that Winge 
(1915, p. 15) found that cod living around the Faroe Islands usually form only about 
12 circuli on their scales during their first year of life, much fewer than Nantucket 
cod, led to an examination of cod scales from various localities along the New England 
coast. The chief object of this was to determine whether there was a noticeable 
difference in the first-zone circulus count, on the average, between the cod living to the 
northward of Cape Cod and those living to the southward; and, if so, whether the 
difference was great enough and consistent enough to separate the New England 
cod into two or more great stocks of fish. 
