84 
BULLETIN OF THE BUREAU OF FISHERIES 
It is a general belief that it requires about six to eight weeks from the time cod 
eggs are hatched until the fry reach the permanent bottom-dwelling stage, though 
there is certainly much variation in this respect. 
LOCAL PRODUCTION OF COD ON NANTUCKET SHOALS 
Cod spawn on Nantucket Shoals from November to April, but chiefly during 
December and January. As the circulation of the water and to some extent its 
temperature on and near Nantucket Shoals, govern the destiny of the cod eggs 
spawned there, it will be of interest to consider whether many of the resultant eggs 
and larvae may be expected to remain there in large numbers and so to maintain the 
stock of Nantucket Shoals cod by local production, or whether they tend to drift 
away. 
For the winter period we have almost no data on the nontidal current for the 
Nantucket Shoals region that would bear on the drift of cod eggs spawned there 
other than that compiled by Bigelow (1927, p. 864) from the current measurements 
made by the United States Coast and Geodetic Survey in 1913-14 at Nantucket 
Lightship. These measurements, each of 29 days’ duration, showed a dominant set 
averaging 5.3 miles per 24 hours N. 86° W., during October, when very few cod spawn 
on the shoals, while during each of the months from November to March, with the 
exception of January, covering the chief spawning season, the set was toward the 
east and south quadrant, its mean direction S. 51° E.; its mean velocity 2.6 miles 
per day. In the spring, by which time nearly all the local spawning has been com- 
pleted, the set was again toward the north and west, the average for April being 
N. 75° W. at 1.4 miles and for May N. 62° W. at 4.3 miles per 24 hours. 
It is true that in the summer Bigelow (1927, fig. 174) found that the dominant 
drift divides on Nantucket Shoals, one part going in a general westerly and the 
other in a general easterly direction. But as we have no proof that this condition 
obtains in winter, and some indication that it may be altered, no sound discussion 
on the subject, for that season, can be given at the present time. 
A good series of winter temperatures is lacking for Nantucket Shoals, but, judging 
from the 10° to 12° C. surface records obtained in October, it is probable that they 
would range from an average of about 8° C. for November to the 2° to 3° C. obtained 
in late February (1929) by the Albatross II. The incubation period for cod eggs 
at these temperatures ranges from about 11 to 23-28 days. 
If the Nantucket Lightship winter-current measurements are typical for most 
of the shoals each year, then it is apparent that the southeastward drift of 2% to 3 
miles per day would carry off most of the cod eggs spawned there before they hatch 
and that the resultant fry would travel considerably farther before reaching the 
bottom stage. Consequently, it may be accepted that only a negligible part of the 
cod living on Nantucket Shoals grow up there from eggs produced locally. Hence, 
we must look elsewhere for the source of the small cod fry that are known to be present 
on Nantucket Shoals in the summer (p. 91). 
THE PROBABLE DRIFT OF COD FRY FROM OTHER REGIONS TO NANTUCKET SHOALS 
It is probable that during most of the winter almost every square mile of water 
off the New England coast contains some cod eggs, larvae, and fry; for spawning 
occurs on suitable grounds, both* inshore and offshore, over a large part of the Gulf 
of Maine and through a period extending from October to April or May. The 
number of fish which spawn in this region each year is very large and the number 
of eggs produced is enormous. 
