Fishery bulletin of the Fish and Wildlife Service - NOAA

BIOLOGY OP THE ATLANTIC MACKEBEL 189
current; as post-larvae, with capable fins, they were able to swim and exercised this
faculty. The change in locomotive ability coincided with change in method of
transport.
Thus far, attention has been focused on the mam centers of larval concentration.
It will have been noted in figure 13 that there were indications of a smaller body of
larvae not included in the groups whose centers were followed. This body probably
became separated from the southern center about May 23, when the center was
at its extreme southerly position, and, as previously pointed out (p. 187), there Wfis a
spread to Chesapeake II and III and Wmterquarter III, probably consisting of only
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.—Drift of post-larvae of the В group compared with wind movement, as recorded at Nantuoket Shoals Lightship.
those larvae that were at the interface between the accumulating surface water and the
outward streaming subsurface layer (p. 187). Having been caught in this outward
and perhaps somewhat northerly flow, their northward drift could start sooner and
would take place farther offshore than the drift of the southern center itself. With
this in mind, it is easy to account for the catches at Atlantic City IV on cruise IV
and at Montauk II and No Man's Land II on cruise VI. That they did not appear
on other cruises is not surprising, for their numbers were few (1,1, and 2 were caught
at the respective stations above mentioned) and as the result of chance fluctuations
in random sampling they could easily fail to appear in our hauls.
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