248 



BULLETIN OF THE BUREAU OP FISHERIES 



when the temperature was near the maximum for the year, and at localities as 

 widely separated as the eastern basin (station 10304), the mouth of Massachusetts 

 Bay (station 10306), and the western basin (station 10307), is an interesting and 

 an unexpected find, for we have seldom found more than two or three thousand 

 per square meter even during its years of abundance. 



The numbers per square meter can not be stated for December, 1920, and 

 January, 1921, when M. longa was nearly universal in the northern parts of the 

 gulf, for want of vertical hauls; but although the percentages of M. longa among 

 copepods as a whole averaged larger then than in any other month except August 

 (table, p. 304), the total catches of copepods were so scanty that the number of speci- 

 mens concerned was small. Even during its periods of maximum abundance M. 

 longa has never been more than a minor element in the total copepod population 

 of the gulf, the average percentages in the vertical hauls for 1915 and 1920 combined 

 being as follows at the stations at which it occurred: 



Months 



February 



March 



April 



May 



Average 

 percentage 



Months 



June 



August 



September 

 October. .. 



Average 

 percentage 



17 



4 



If the stations at which it was not taken be counted in, the February percentage 

 is thereby reduced to 2 per cent, August to 12 per cent, and percentages for all the 

 other months by 1 to 3 per cent. The table suggests that in its years of abundance 

 in the gulf M. longa is relatively least important in the plankton at seasons when 

 the Calani are most plentiful, irrespective of fluctuations in its own numerical 

 strength and in the generality of its distribution over the gulf. 



Vertical distribution. — In the polar basin north of Europe and Asia M. longa 

 seems indifferently distributed from the surface downward to 300 meters (Sars, 

 1900), and Nordenskiold (1882) has given an interesting account of its occurrence 

 in great abundance along the tide line in water-soaked snow in Spitzbergen. 



Passing southward in the eastern Atlantic, European observers have described 

 this species as tending to keep deeper and deeper. Thus, it occurs chiefly between 

 50 and 200 meters in the seas between Spitzbergen and Greenland, though to some 

 extent at the surface (Damas and Koefoed, 1907); in the Norwegian seas (Damas 

 and Koefoed, 1907) and fjords (Sars, 1903) it has been taken in greatest number 

 below 200 meters, rarely at the surface; chiefly below 300 meters between the Faroes 

 and Iceland (Damas and Koefoed, 1907) ; and its most southerly record — west of 

 Ireland — was from 540 to 720 meters (Wolfenden, 1904). 



It likewise occurs more regularly in the deeper levels than at the surface off 

 the American coast, figuring in only 30 per cent of the surface hauls in the Gulf 

 of Maine for the spring of 1920, contrasted with its presence in 46 per cent of the 

 verticals during that same period; but it is worth noting that at two stations it 

 was taken in the surface but not in the vertical hauls (stations 20081 and 20092), 



