Fishery bulletin of the Fish and Wildlife Service - NOAA

BIOLOGY ОБ 1 THE ATLANTIC MACKEREL 183
DRIFT AND MIGRATION
The current system in the waters overlying the continental shelf between Cape
Cod and Cape Hatteras has yet to be studied. Evidences collected during this investigation
from releases of drift-bottles and computations of dynamic gradients, the
latter subject to large errors of interpolation, were not sufficiently conclusive to
deserve publication. They indicated slight tendency for movement in a southwesterly
direction parallel to the coast, probably not strong enough to transport eggs
and larvae of the mackerel important distances.
On the other hand, evidence from the distribution of mackerel eggs and larvae
themselves leads to definite conclusions. From the growth curve of larvae, figure 8,
or from the position of homologous modes hi the deviation curves, figure 7, it is possible
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1.4
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а
оо 1.0
0.8
0.6
0.4
NORTHERN
PIKE
10 го 30 40 50 60 70 80 90 100
AGE, D AYS
FiOTTBi 12.—Growth of northern pike, herring, mackerel, and haddock.
50
40
30
20
10 Ê о
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to ascertain the lengths attained by certain groups of larvae at each successive cruise.
By plotting the geographical distribution of larvae of these particular lengths in successive
cruises, as in figure 13 based on the S series, then: movements may be followed.
In general, this series represents a population spawned over the continental
shelf off the New Jersey coast. Larvae hatched from these eggs remained in this
area until they reached a length of 8 mm. about a month later. Thereafter, there
was a northeasterly shift which brought the population to the region just south of
Long Island at the end of their second month when they were about 20 mm. long.
Movement toward the northeast probably persisted still longer, for the only individuals
large enough to have been members of this series were taken at stations along the east
coast of Massachusetts (Chatham II and Cape Anne II in table 20) durjng the cruise
of July 14 to 28. Although there is local spawning hi Massachusetts Bay, it is unlikely
that it was responsible for these large individuals, because spawning usually is later
in Massachusetts Bay, and the locally produced larvae could not have grown to as
large a size as the 37- and 51-mm. post-larvae taken on July 22.