PROGRESS IN BIOLOGICAL INQUIRIES, 1926 603 
(from October to April) makes it particularly difficult to interpret the first 
year’s growth. To assist in this all young cod, as well as pollock and haddock, 
are preserved. 
According to scale growth, I find that cod from southern Massachusetts, of 
1, 2, and 8 years of age, are about 7, 14, and 21 inches in length; and cod from 
eastern Maine are 6, 12, and 18 inches in length. After the third year, the 
increase in length becomes less with each added year. Our recapture records 
show that the actual increase in growth made during one year by tagged cod 
from Maine was about 4 inches from the third to the fourth year, the same 
from the fourth to the fifth, 3144 inches from the fifth to the sixth, and 2% 
inches from the sixth to the seventh year. Year classes, as determined by 
length frequencies, compare well with the lengths of the fish as calculated from 
the scales, at least up until the fourth year. Little can be done with the length 
frequencies of the older fish. 
The cod problem is a complex one and it is necessary to study the fish in 
many localities and under varying conditions. In general, large fish are found 
offshore and small fish inshore. The smallest cod of 1,000 caught on Georges 
Bank last summer was 20 inches long; whereas, out of the same number of fish 
caught within a few miles of shore, it frequently happens that as many as 80 
or 90 per cent are below 20 inches. Each cod ground affording differing physi- 
eal conditions has its own peculiar stock of fish, and there appears to be no 
general intermingling of fish from the various banks. It is true that large 
numbers of spawning cod collect in the shore waters of New England through- 
out the winter, but I am not prepared to say at this time where they come 
from or where they go after spawning. A few of our tagged fish have been 
caught among these spawners, but only scattering records and not enough to 
indicate a migration from the tagging ground. 
Cod can adjust themselves to diverse living conditions; or at least we find 
them living under differing conditions. Comparing eastern Maine with Nan- 
tucket Shoals, both of which places have a year-round cod population, the 
Maine fish seldom have a bottom-water temperature greater than 11° C., which 
has been considered the upper limit for the cod. Yet Nantucket cod withstand 
as much as 14144° C. Maine cod feed largely on small crustaceans, such as 
shrimp and small hermit crabs, whereas Nantucket fish usually are gorged with 
large Cancer crabs. Maine cod appear to grow more slowly than Nantucket 
cod. The only migration shown by Maine cod has been entirely to the eastward 
to the coasts of Nova Scotia. Nantucket cod, if they migrate, go west and 
south, or to the Chatham grounds a few miles to the northeast. Out of 
thousands of cod tagged in eastern Maine, from 65 to 75 per cent were less than 
18 inches in length; while on Nantucket Shoals, up to 1925, the percentage of 
these small fish was one-fourth to one-half of 1 per cent. 
Another problem arises from the fact that while cod of one locality may 
behave the same for a period of years, an abrupt change may then occur. 
Nantucket cod, as regards the stock of fish and their migrations, were much 
- the same for the three years 1923 to 1925; but in 1926 we found the stability 
of the fish population had in some way become unbalanced. Whereas, fish from 
22 to 32 inches in length largely predominated during the first three years, in 
1926 we found this group in the minority and that a new stock of fish, of 14 to 
20 inches, had taken their place. Where the larger fish went and from whence 
the smaller ones came we have not yet ascertained, but are waiting for our 
tag returns to give some indication of what happened. 
The cod program must continue for some years before we can hope to give a 
comprehensive account of the fish’s life history. 
MR CEO Ricu. What is the age of the small fish that came in this 
year # 
Mr. Scuroeper. There was a combination of two or three year fish. 
The 2-year-olds were extremely scarce the previous three years, but 
in the fall of 1925 we noted a change. Some of these small fish 
came in the fall of 1925. The previous fall some indication was 
noted that the change was about to occur when the small fish com- 
prised about 8 per cent of the total, instead of one-fourth or one-half 
of 1 per cent, and then we thought something would happen. If you 
fish on any offshore grounds you can get absolutely nothing out of 
length frequencies; it seems as though all the lengths are represented, 
