90 
BULLETIN OF THE BUBEAU OF FISHERIES 
Volumes of 'plankton per square meter, western basin 
Date 
Cubic centi- 
meters of 
zooplank- 
ton per 
square 
meter 
Date 
Cubic centi- 
meters of 
zooplank- 
ton per 
square 
meter 
Feb. 23,1920 
175 
June 26,1915 
250 
Mar. 24, 1920 
95 
July 15, 1912. 
65 
Apr. 18^ 1920 
150± 
Aug. 22,1914 
200 
May 5,1915 
250 
Aug. 31,1915. 
165 
There is, likewise, less fluctuation with the seasons on the western part of Georges 
Bank than on the eastern. The largest volume of plankton per square meter yet 
recorded for the Gulf of Maine was 425 cubic centimeters in the eastern side of the 
basin on September 1, 1915 (station 10309), while the smallest was a bare trace. 
In fact, the animal population may be so sparse locally that a vertical haul may catch 
nothing at all, as has been our experience at several stations along the coast of Maine 
and in the Grand Manan Channel (p. 84) ; but even then, a half hour’s tow with the 
horizontal net has invariably yielded a few copepods or other animals, proving that 
although the planktonic community may fall to a very low ebb, indeed, at its season 
of scarcity, it never vanishes wholly from any part of the gulf at any time of the year 
DENSITY OF ASSOCIATION OF THE ZOOPLANKTON 
A statement of the volume of zooplankton existing in the total column of water 
below any chosen unit of sea area — e. g., each square meter — serves to illustrate the 
total regional and seasonal production of the gulf ; but unless the water in question 
be very shallow, it throws little light on the density in which the animals concerned 
are congregated, because the catch of the vertical haul may be distributed generally 
over a column so long that even a considerable volume of plankton might mean only a 
sparse population. To meet this need, another unit of measurement is required, the 
one usually employed in other seas, and of which I have made use in previous re- 
ports (Bigelow, 1915 and 1917), being the volume of plankton present in each cubic 
meter of water. This, of course, is simply the product of the volume per square meter 
of sea surface divided by the depth (in meters) covered by the haul in question. 
Were the zooplankton of the gulf uniformly distributed from the surface down 
to bottom, this simple calculation would not only "establish the relative richness of 
different regions in plankton, and hence in food for the pelagic fishes ” (Bigelow, 1915, 
p. 327), a question naturally of much importance in the economy of the gulf, but go 
far to explain many biologic problems even more far reaching. Unfortunately for 
the statistician, however, such is not the case, all our experience tending to show that 
the zooplankton is often more or less stratified and that the degree of stratification, 
varies widely from place to place with the time of day and with the change of the 
seasons. Consequently, the results always require analysis in the light of any 
information bearing on the vertical distribution of the planktonic communities 
represented in the catches in question. Otherwise one is apt to be led to conclusions 
so widely astray as to be worse than none. 
