PLANKTON OF THE GULF OF MAINE 75 



Desert fish may well reach Massachusetts Bay in their journey by the time they 

 are 10 to 15 millimeters long, if they remain in the superficial water layers. If 

 they sink to lower levels, as it is practically certain that many of them do, their 

 involuntary migration during this stage probably is not so extensive, there being 

 reason to believe that the general set is more rapid above than below 40 to 50 meters ; 

 but whatever depth they seek within the 100-meter contour (which in general limits 

 the offshore dispersal of both eggs and larvre in this side of the gulf), the majority 

 of them will tend in the same general direction. Similarly, the larva? hatched from 

 buoyant fish eggs spawned off Machias, where considerable numbers are produced, 

 might well travel as far as Cape Elizabeth before attaining the sizes we have recog- 

 nized in the tow nettings. 



The distribution of the buoyant eggs of the cod and flatfish families in the 

 gulf bears precisely the relationship to that of the older larval stages (fig. 35) which 

 involuntary migration of this sort would produce. In fact, something of the kind 

 might safely have been prophesied from what is known of the circulation of the 

 gulf; and I believe it safe to assert that the great majority of the larval fishes 

 hatched from buoyant eggs spawned in the zone from 10 miles or so outside the outer 

 islands out to the 100 or 150 meter contour, between Cape Elizabeth and the Bay of 

 Fundy, drift a greater or lesser distance around the periphery of the gulf toward the 

 west and southwest (if they survive as long as three weeks or a month), though this 

 drift may be interrupted or even reversed on any given day or over a period of several 

 days. They may tend to hug the coast, as it seems Mavor's (1920) first series of 

 drift bottles did in 1919 (this probably is the usual event in spring), or swing more 

 offshore, and so, if they live pelagic long enough, come around to the northeastern 

 corner of the gulf as other drift bottles released in the summers of 1922 and 1923 

 have done. The variations in the dominant set are not well understood, but in any 

 case they will tend to follow an anticlockwise and eddying course. 



Thus, fish eggs and larva?, and for that matter every member of the plankton, 

 animal or vegetable, tend to follow the same peripherical migration zone as do the 

 immigrants that enter the eastern side of the gulf in the upper 50*meters (p. 64). 

 Only such buoyant eggs as are spawned among the islands, in bays, or close in along 

 shore (as most of the dinners are) are likely to escape this dominant set. 



At the times when the dominant drift of the surface water follows the coast 

 line closest, south toward Cape Ann, Massachusetts Bay probably acts to some 

 extent as a catch basin for all sorts of flotsam from the north, living, of course, as 

 well as dead, as it did for certain of Mavor's drift bottles. The chart (fig. 35) sug- 

 gests that larva? that pass Cape Ann tend to be caught up in the back water of the 

 bay, to remain there until they abandon the pelagic life for the bottom. Thus, it 

 is probable that the rich fish fauna of the bay and its adjacent waters is regularly 

 recruited from the north and east. 



Similarly, the abundant occurrence of young pollock at Woods Hole in late 

 spring (fry so small that they are evidently the product of the previous winter's 

 spawning) is clear evidence of a migration southward along and around Cape Cod 

 from the very productive spawning grounds at the mouth of Massachusetts Bay, 



