PLANKTON OF THE GULF OF MAINE 277 



We have found it at 77 per cent of the stations on Georges Bank and the shelf 

 off Marthas Vineyard, 72 per cent of the stations in the basin as inclosed by the 100- 

 meter contour, S6 per cent in the coastal zone inside 100 meters from Cape Cod to 

 Grand Manan, 77 per cent in the coastal zone along western Nova Scotia, 86 per cent 

 in the eastern and northern channels, but at only half the stations on Browns Bank 

 and 65 per cent of the stations outside the continental edge. 



Thus, on the whole, Pseudocalanus elongatus is somewhat more nearly universal 

 close along shore than out at sea in the gulf (fig. 83) ; but the regional difference 

 is so small inside the continental edge that it may be of no general significance and 

 merely the result of one haul chancing to pick up and another to miss scattered 

 specimens at times and places where the species is scarce. Probably the apparent 

 infrequency of this copepod on Browns Bank is to be explained in this way. 



Although P. elongatus is so nearly universal, the numbers actually present at 

 any given time have usually averaged larger in the basin, in the entrant channels 

 (northern and eastern), and along the offshore slope than anywhere in the coastal 

 belt of the gulf inside the 100-meter contour. The locations of the stations where 

 the number of specimens per square meter has been larger than the average for the 

 respective month and year afford a graphic illustration of this localization of the 

 rich catches in the deeper parts of the gulf, for 22 out of 36 have been outside 

 and only 14 inside the 100-meter contour (fig. S4). Otherwise expressed, only 20 

 per cent of the shoal catches have been above average, as contrasted with 40 per 

 cent of the deep hauls. 



The "rich" catches in the basin have been distributed indifferently from the 

 west side to the east; but this correlation between the abundance of Pseudocalanus 

 and the topography of the bottom does not apply in the southern part of the area, 

 for rich hauls have been made over the outer part of Georges Bank and on the con- 

 tinental shelf off Marthas Vineyard, while all records of the species so far obtained 

 from farther west and south than this along the coast have been well inside the 

 100-meter contour. 



Vertical distribution. — In the northerly part of its range P. elongatus has been 

 found commonly at the surface in other seas as well as at various deeper levels, and 

 its presence is established down to about 900 meters by the use of the closing net 

 (Wolfenden, 1904), but its chief zone of abundance lies above 200 meters. The 

 Canadian fisheries expedition took it as regularly at the surface in the Gulf of St. 

 Lawrence as in deep tows down to 150 meters, and apparently about as abundantly. 

 The great majority of records for this species in the Gulf of Maine have been 

 based on hauls from depths greater than 50 meters, not so much because of a con- 

 centration in deeper water as because the deeper hauls, horizontal or vertical, have 

 been the basis for most of the fists of copepods. During the Albatross cruise of 1920 

 Pseudocalanus was found regularly at the surface as well as at deeper levels from the 

 last week in February until the last week in March (about 90 per cent of the stations), 

 irrespective of locality, but less frequently (only about 42 per cent of the stations) 

 through April and May (table, p. 303). It is probable that this change resulted from 

 a general tendency on its part to desert the uppermost stratum as the season advances. 

 It was detected at only three of the six stations where the surface net yielded enough 



