BIOLOGY OF 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 in- 

 vestigation 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 south- 

 westerly 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 in the deviation curves, figure 7, it is possible 



50 

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(9 



8 uj 



0.4 



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70 



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AGE, DAYS 

 Figure 12.— Growth of northern pike, herring, mackerel, and haddock. 



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 suc- 

 cessive cruises, as in figure 13 based on the S series, their 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) during the cruise 

 of July 14 to 28. Although there is local spawning in 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. 



