BIOLOGY OF THE ATLANTIC MACKEREL 



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 main 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 was a 

 spread to Chesapeake II and III and Winterquarter III, probably consisting of only 



76 



— r— 



75 



— r~ 



73 



70 



69 



(7-23) IX O 



WIND 

 MOVEMENT 



~3X O *■ nVTT 



(6-6) (6' 



76 75 74 73 72 71 70 69 



Figube 16.— Drift of post-larvae of the S group compared with wind movement, as recorded at Nantucket 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. 



