PLANKTON OF THE GULF OF MAINE 145 



Th. lorujicaudata, a species equally northern in its faunal status, then extended south- 

 ward beyond the latitude of Delaware Bay. In short, the Gulf of Maine and the 

 continental shelf abreast of Marthas Vineyard and Nantucket together form the 

 southern outpost of Th. raschii in summer. 



Thysanoessa raschii is apparently no more plentiful in the gulf in autumn, 

 for we have not noted it either in October or November and only twice during our 

 December-January cruise of 1920-1921 (occasional specimens off Cape Elizabeth 

 on December 30, station 10494, and off Lurcher Shoal on January 4, station 

 10500). Neither did we detect Th. raschii in any of the tows made off Gloucester 

 from November, 1912, until March, 1913, but it swarmed a few miles north of 

 Cape Ann during that April. The first specimens were noted on the 22d in the 

 neighborhood of the Isles of Shoals; on the 23d (when, as it chanced, none were 

 taken) Mr. Welsh wrote in his field notes of " the pollock schools feeding on shrimps, 

 which were also in dense schools" (Bigelow, 1914a, p. 408); and a large catch of 

 them made off Boon Island on the 25th, when Welsh saw "the feed (shrimps) 

 breaking water trying to get away from the pollock, which are after them," estab- 

 lished their identity as this species. At that time the shrimp, as he noted, were 

 concentrated "in dense swarms apparently 6 inches to a foot below the surface," 

 and although these schools had dispersed by the first week in May, so that they were 

 no longer in evidence from the vessel, he still found them near the Isles of Shoals 

 in abundance on the 12th and 13th of the month. There is no knowing how much 

 longer they persisted there, for we did not revisit that region until the following 

 August, when they had disappeared. 



We have never found this species so plentiful in the gulf since then, but in 1920 

 it appeared at about 25 per cent of the stations occupied by the Albatross in March 

 and April, 78 twice in considerable numbers — that is, off Cape Elizabeth on March 4 

 (station 10059), and a few miles north of Cape Ann on May 8 (station 20122). 

 It again appeared in abundance in this same general region in the spring of 

 1925, when tows from the Fish Hawk at two stations 5 to 7 miles southwest from 

 the Isles of Shoals yielded large catches of Th. raschii on April 7, with a few Th. 

 inermis. 



The facts just outlined are enough to show that the spring is the period of 

 maximum abundance, the summer and autumn of minimum abundance, for Th. 

 raschii in the Gulf of Maine, and the coastal zone between Cape Ann and Cape 

 Elizabeth a center of abundance for it. Most of our records for it have been 

 located either around the periphery of the gulf within or close to the 100-meter 

 contour or in the shoal waters over Georges Bank (fig. 52) , but more data are needed 

 to show whether this apparent concentration in the coastal zone is significant. 



Most of the specimens of Th. raschii that Welsh took during its period of abund- 

 ance in April and May, 1913, were large, and we again found large adults in Ipswich 

 Bay — that is, in the same general region — on May 8, 1920 (station 20122); but 

 with this species so rare in the gulf in summer, few, if any, of the larvae resulting 

 from such local centers of reproduction can survive there. Thus it is chiefly as 



"Stations 20044, 20059, 20060, 20070, 2O073, 20075, 20080, 20085, 20092, 20093, 20096, 20097, 20099, 20102, 20105, 20116, 20122, and 

 20125. 



