138 BULLETIN OF THE BUREAU OF FISHERIES 



the gulf, as well as close up to the land off Cape Sable and in Eastport harbor during 

 the warm months, shows that it is not the shoalness of the water which holds it 

 offshore, but either some influence of the coast line itself or the physical state of the 

 water. Thus it is rather more oceanic in the gulf than its omnipresent and much 

 more plentiful companion, the copepod Calanus finmarchicus, for the latter thrives 

 right up to the outer islands and headlands, though its adults are seldom abundant 

 in inclosed waters. 



The term "oceanic," however, as applied to Thysanoessa inermis, does not imply 

 that it reaches the Gulf of Maine from the warm water of the Atlantic Basin to the 

 east and south. On the contrary, we have never found it in our hauls outside the 

 continental edge, either east or west of Cape Cod, except at one station (10349, July 

 24, 1916), where low temperature proved that the inner edge of the "Gulf Stream" 

 lay some distance farther offshore. Nor did Hansen (1915) find it in gatherings 

 taken over the slope abreast of the gulf, where other euphausiids — e. g., Nemato- 

 scelis — occurred in abundance, though he records it from various localities over the 

 outer part of the continental shelf within the limits of the gulf — e. g., off Marthas 

 Vineyard, near Browns Bank, and south of Nova Scotia. It is evident from this that 

 the warm and highly saline tropical water, which is never far out beyond the edge 

 of the continent in these latitudes, is an effective barrier to the offshore dispersal of 

 Th. inermis off the eastern United States, although it ranges southward regularly to 

 southern New England every summer, and even accompanies the Calanus com- 

 munity as far south as the latitude of Chesapeake Bay in cool summers (e. g., 1916) 

 and probably every winter. 



In all this its occurrence in American waters parallels its distribution on the 

 other side of the Atlantic, where it is distinctively arctic-boreal, as Kramp (1913, 

 p. 544) points out, occurring chiefly in the northern Atlantic and in the adjacent parts 

 of the Arctic Ocean from Franz Josef Land to West Greenland, and southward as 

 far as the North Sea and the waters around Ireland. 



Thysanoessa inermis is present in the Gulf of Maine throughout the year, as 

 proven by the fact that we have taken it there throughout the spring and summer, 

 at several stations in September and October of 1915, twice (out of five stations) in 

 November in 1916, and at about half the stations occupied during our midwinter 

 cruise of 1920 and 1921. As I have just pointed out, winter is its season of greatest 

 abundance at St. Andrews, but it shows no apparent tendency to work inshore off the 

 coasts of Massachusetts at that season, for we did not detect it at all in tows taken 

 near Gloucester every two weeks throughout the winter of 1912 and 1913. 73 



The most notable seasonal fluctuation in the distribution of Th. inermis within 

 the gulf (supposing its status in 1920 to be representative) is that it almost totally 

 disappears from the southern deeps, from the eastern channel, and from Georges 

 Bank in March and April, although it occurred at about 50 per cent of our stations 

 around the coastal belt at that season (fig. 49). Our failure to find it over the eastern 



« For its occurrence from 1912 to 1916 see Bigelow, 1914a, p. 411; Bigelow, 1917, pp. 282 and 283; and Bigelow, 1922, pp. 133, 136, and 

 150. In the spring of 1920 it was detected at Stations 20046, 20049, 20054, 20057, 20059, 20060, 20070, 20073, 20075, 20079, 20080, 20085, 20086, 

 20088, 20092, 20093, 20094, 20097, 20099, 20100, 20101, 20102, 20105, 2O100, 20116, 20119, 20122, 20125, and 20126; as well as at the following 

 stations from December, 1920, to January, 1921: 10490, 10494, 10497, 10499, 10500, 10502, and at stations 10507, 10508, 10509, and 10510 

 in March, 1921. 



