188 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



confined to the upper stratum (p. 172); it could and probably did carry a few that 

 happened to be near the interface as indicated by the light spread of larvae southward 

 and outward to Chesapeake II and III and Winterquarter III. 



While this accounts for the halting of southerly drift of the southern center and 

 its increase in relative numbers, there is still to be considered the apparently too rapid 

 drift of this center northward when the wind direction was reversed. Let it be sup- 

 posed that the aforesaid piling-up of surface waters took place more rapidly than could 

 be counterbalanced by subsurface flow. Then the sea surface would actually have 

 risen and remained at a higher level as long as the wind continued to transport surface 

 water to the area faster than the subsurface water could flow away. Then when the 

 wind reversed its direction, the energy so stored would be released and act in the same 

 direction as the wind. The two forces together would produce a faster drift than 

 could result from the wind force alone, and thus account for the high rate of move- 

 ment of the southern center between May 22 and June 3. 



Whether the interactions of the wind forces and water movements here postulated 

 were theoretically probable from dynamic considerations must be left to the physical 

 oceanographer. He can find here an example of biologically marked water probably 

 of considerable aid in the deciphering of the pattern of circulation in shallow water, 

 where difficulties of dynamic analysis are heightened by topographical features, and 

 where a better understanding would be of greatest practical use in dealing with fishery 

 problems. 



Whatever the outcome of any future examination of the dynamics of this situa- 

 tion, the outstanding resemblance of the main features of wind movement to larval 

 drift, together with the fact that deviations from the parallelism between the two 

 have a plausible though not proved explanation, leaves no doubt that the larvae 

 (and the water with which they were surrounded) were drifted from place to place 

 by the wind's action on the water, and that this alone accounted for their movements 

 until they reached the end of the larval stage at a length of about 8 to 10 mm. and 

 entered upon the post-larval stage. 



Subsequently the movement of larval concentrations corresponded less perfectly 

 with that of the wind (fig. 16). Between cruises VI and VII, when there was a gentle 

 easterly wind movement, the post-larvae also moved eastward, but proportionately 

 father than might have been anticipated from the moderate wind movement. Between 

 cruises VII and VIII, when there was a northeasterly wind movement, they moved 

 northwesterly. After cruise VIII it is difficult to be sure of the homology of the 

 group under consideration, but the only post-larvae (lengths 37 and 51 mm.) of 

 cruise IX identifiable as belonging to this group were caught at Chatham II and Cape 

 Ann II, off eastern Massachusetts. The indicated movement was in the same general 

 direction as the prevalent strong winds, but again sufficiently divergent to indicate 

 some independence. Since the drift of water under impulse from the wind accounts 

 for only a portion of their movement and since such evidence as is available on 

 residual surface flow in this region 18 indicates water movement westerly, hence in a 

 direction contrary to the movement of the post-larvae, the evidence does not favor the 

 transport of the post-larvae as purely passive organisms, and it must be concluded 

 that they moved to an important extent by their own efforts. 



This is in complete harmony with their developmental history. As larvae, 

 without swimming organs other than the rather flaccid finfold, they drifted with the 



'• Drift-bottles set out by Wm. C. Herrington (unpublished data) in connection with his haddock investigations in the spring 

 of 1931 and 1932 drifted westward past Nantucket shoals, fetching up on beaches of southern New England and Long Island. 



