PLANKTON OF THE GULF OF MAINE 77 



deeper, and of young haddock still deeper currents, but to what extent this differen- 

 tiates the dispersal of their fry in the gulf from those of the pollock can not be stated 

 until a sounder knowledge of the circulation of the waters of the gulf has been 

 gained. 



It has long been known that the larval and post-larval stages of the hakes (genus 

 Urophycis) are apt to be right at the surface in the Gulf of Maine in summer. They 

 might therefore be expected to follow very closely the tracks of the drift bottles 

 released at that season. Silver-hake (Merluccius) larvas, on the contrary, which are 

 among the most abundant of young fishes in the southwestern part of the gulf in 

 July and August, usually have been taken in hauls from 40 meters or deeper (seldom 

 at the surface), and it would seem that they must -therefore travel with the under- 

 current. In the case of silver hake it is not improbable that some of the larvae that 

 journey down past Cape Cod drift on past Nantucket Shoals toward the south- 

 west. Consequently, eggs spawned in the Gulf of Maine may contribute to the fry 

 found west of Nantucket in summer, though most of these are the result of local 

 propagation (Bigelow and Welsh, 1925, p. 395). 



It is equally possible that part of the young silver hake circle eastward over 

 the northern part of Georges Bank, and so northward into the gulf again, for drift 

 bottles released on a line running southwest from Cape Cod have shown a division 

 in this respect, many of the outer ones having gone westward and some of the inner 

 ones eastward, but we have found no Merluccius larvae in any of our July towings 

 over the banks, although they are abundant off Cape Cod during that month. 



I have previously (Bigelow, 1917, p. 279) suggested the possibility of a passive 

 migration of cod and haddock from the western part of the gulf out onto Nantucket 

 Shoals and to the western parts of Georges Bank, where we have since found young 

 haddock in some abundance floating commensal with medusae in July (Bigelow and 

 Welsh, 1925). 



The drift of the haddock eggs that are spawned in enormous numbers on the 

 eastern part of Georges Bank in spring (p. 37; and Bigelow and Welsh, 1925, p. 439), 

 and of the resultant larvae, is a question of great interest. A considerable propor- 

 tion of these may take to the bottom on more westerly parts of the bank, because 

 the northern part of this spawning ground seems to be affected directly by a set 

 from the northeast during the critical season; but at the time of our Marcli and 

 April visits thither in 1920 the presence of newly spawned eggs in abundance right 

 out to the 1,000-meter contour proved that a drift out to sea was then taking place 

 from the southern point of the bank. 



Eggs subject to this drift must suffer one of two fates. Probably they would be 

 caught up in the band of cool mixed water along the continental slope, in which case 

 the eggs and larvae might again be swept in on the shelf somewhere to the westward 

 by some incurving swirl in the complex interaction of warm and cold waters, or, 

 circling to and fro, come in again on Georges Bank. If they drifted farther offshore, 

 but still not far enough out to reach water of fatally high temperature, they would 

 probably tend to travel to the northeast. Therefore, as Doctor Huntsman suggests 

 in a recent letter, it is possible that the Georges Bank spawning ground, which is 



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