MIGRATIONS OF COD 
119 
that southern New England cod form the bulk of the fish which occupy these 
wintering grounds is indicated by the paucity of recaptures there of fish tagged to 
the northward and eastward of Cape Cod and by the general similarity in length 
frequencies between the population in this wintering region and the summer cod on 
Nantucket Shoals. In the spring the fish return eastward, the majority of them 
stopping to summer on Nantucket Shoals, but others, chiefly the larger fish, most 
of which probably came from the north and east of Cape Cod, continue on to deeper 
water. 
4. The number of cod which take part in this migration must be large, for the 
catch made each winter between Rhode Island and Delaware has ranged between 
three and five million pounds. 
5. Many of the cod spawn on these wintering grounds, but whether most of the 
resultant larvae are carried southward by the currents and are lost or whether many 
return to New England waters and thus help replenish the stock there is not known 
at this time. 
6. The earliest migrants go west from Nantucket Shoals about the middle of Octo- 
ber the movement of fish reaching its height during November and subsiding toward 
the end of December, after which it virtually ceases. The migration back to the 
eastward occurs chiefly during March and April, although a few fish may return as 
early as December and a few as late as May. 
7. Temperature, either directly or indirectly, may be the cause of this migration, 
for the cod leave in the fall when the water begins to cool and return eastward in 
the spring when it begins to warm, although there seems to be no correlation between 
a particular temperature and the coming or going of the fish. 
8. During the summer a cod is rarely caught west of Rhode Island and relatively 
few even off the latter coast, although the summer bottom temperature in the New 
York-Delaware region is as low or lower over certain of the grounds frequented by 
the cod in winter than it is on Nantucket Shoals. 
9. Part of the cod living on Nantucket Shoals emigrate eastward to the Chatham- 
South Channel region during certain summers. This emigration was most apparent 
during the three years from 1923 to 1925, when most of the Nantucket cod averaged 
upward of 25 inches in length, and was scarcely noticeable, by means of tagged fish, 
during the three years from 1926 to 1928, when the fish were smaller. Not only 
the size of the fish but temperature, too, appears to influence this emigration, for it 
was largest during that year (1925), which was somewhat warmer on Nantucket 
Shoals than any of the others. 
10. Fewer cod took part in the summer eastward emigrations than in the fall 
westward migrations, for length-frequency distributions, recaptures of tagged fish, 
and the abundance of the fish as shown by tbe catch per unit of effort, showed that 
a large part of the cod population on the shoals remained localized throughout the 
summer. 
11. The average summer cod population on Nantucket Shoals from 1923 to 1928 
might be roughly estimated as between three million and four and one-half million 
adult and nearly adult fish. 
12. Tbe number of grown cod which live on Nantucket Shoals appears to be fairly 
uniform from year to year. Losses are caused by (a) deaths from natural causes, 
(b) fish taken by the fishery not only on Nantucket Shoals but also on the wintering 
grounds to the westward, and (c) emigrations to other regions. The gains are brought 
