94 



BULLETIN OF THE BUREAU OF FISHERIES 



nearly correct picture of the summer state results from the assumption that the 

 entire catch of zooplankton in the vertical net at that season was taken below 10 

 meters at each station, but that it was only one-third as dense as the ostensible 

 volume per cubic meter below 100 meters, and correspondingly concentrated above 

 that level. The results of such a calculation for 1914 are given in the following table: 



Volumes of plankton per cubic meter (in cubic centimeters) between the depths of 10 and 100 meters, 



July to August, 191 4 1 



i For tables of the volume per cubic meter for July and August, 1913, and for May to October, 1915, see Bigelow, 1915, p. 328, 

 and 1917, p. 314. 



The most instructive feature of this table is its demonstration that, although 

 the total amount of plankton present below any given unit of the sea's surface rules 

 larger in the deeper parts of the gulf than in the shallower water, as a rule it is most 

 densely aggregated in the coastal belt within the 150-meter contour and in the 

 shallows of Georges Bank, no. matter which calculation be employed. This was 

 true, also, in the summer of 1913. In fact, the northeastern part of the deep basin, 

 where the water has proved very productive on several occasions in summer and 

 early autumn, as well as in late spring, has been the only exception to this rule for 

 any time of year. 



Enough hauls have now been made to show that the zooplankton (especially 

 the Crustacea) is usually most densely congregated, summer after summer, in four 

 rather definite areas — (1) over the eastern end of Georges Bank, (2) in the shoal 

 water south of Cape Sable, (3) in the deep northeastern basin, and (4) off Massachu- 

 setts Bay out to the 100-meter contour (fig. 39). At the other extreme the western 

 and southern parts of the deep basin and the coastal belt inside the 100-meter contour 

 east of Penobscot Bay have never yielded as much as 2 cubic centimeters of plankton 

 to the cubic meter of water at any season by either mode of calculation, nor has the 

 water over the coast bank west of Nova Scotia proved productive except for the 

 Pleurobrachia swarms so characteristic of that locality (p. 19). 



