MIGRATIONS OF COD 
111 
This conclusion is supported by the results of our tagging both to the north and 
the south of Cape Cod and was much the same conclusion arrived at by Smith some 
25 years before (p. 8), when he found that none of his cod were reported recaptured to 
the northward of Cape Cod. 
As most of the cod given in Table 41 averaged from 22 to 28 inches long and 
were from 3 to 5 years old, it is apparent that up until that age most of them remained 
in the general vicinity of the region where they first took to the bottom as fry. If 
this were not the case and if there were an extensive intermigration of cod between 
Nantucket Shoals and grounds to the northward, then we could expect very little 
difference in the count of first-year circuli between the fish living to the northward 
of Cape Cod and those living to the southward. 
No scale samples were obtained from cod living in the western part of Georges 
Bank, intermediate between the northeastern part of the bank and the Nantucket- 
South Channel region, so we do not know if the fish from there have a first growth- 
zone circulus count that falls somewhere between 15 and 20. But a sample of scales 
taken from 45 cod caught May 3, 1927, on the Chatham grounds 13 miles northeast 
of the most northern tagging ground on Nantucket Shoals had an average of 18.1 
first-zone circuli, which number falls between the averages of 14.9-15.6 obtained on 
Stellwagen Bank and the 19-20.6 found in the Nantucket-South Channel region. 17 
The fact that the scales of cod caught on the Cholera Bank near New York City 
and off Atlantic City, N. J., agree in circulus count with those from the Nantucket 
Shoals region and disagree with those from the north and east of Cape Cod is signifi- 
cant, for we have here further proof that the grounds off southern New England supply 
a large part of the cod which migrate each winter to the Rhode Island-North Carolina 
region. 
Beyond the first growth zone the differences in scale circulus count between the 
cod living north of Cape Cod and those to the southward tend to disappear, so that 
from the third year on the count is virtually the same for both groups of fish. 
Age and rate of growth of cod as determined from their scales .- — Lea’s (1910) method 
of determining the annual growth 18 of fish by means of their scales has been used by 
various investigators with more or less success. It was based on the supposition that 
the scales and body of a fish grow at proportionately the same rate, at least nearly 
enough so that the lengths calculated for each year of life would be essentially correct. 
Other investigators using this method have found that, although it is workable, cor- 
rective factors must be established for each species because, as Lee (1920, p. 21) 
points out, the ratio of length of the scale to the length of the fish changes with age. 
Thompson (1923, p. 75) points out in the case of the haddock that the scales 
first appear along the flank of the body and then only when the fish has reached about 
3 centimeters in length and that the size of the first platelet is proportionately smaller 
than that of the fish, so that about a half centimeter must be added to the calculated 
first-year size. Scales which appear later on other parts of the body may increase 
this error to as much as 2% centimeters. Cod scales, too, appear when the fry is about 
3 centimeters long, and the first ones are found along the sides of the body. 
n The South Channel scales were obtained from fish caught on the extreme western edge of South Channel in about longitude 
69° 24' W., latitude 41° 17' N., which is to the southward of the Chatham grounds and which might, in fact, be termed the eastern 
edge of Nantucket Shoals. 
18 Annual growth is calculated by measuring the growth zones along any convenient radius on the scale and comparing each 
zone with the total length of the radius selected and the total length of the fish. 
105919 — 30—8 
