PLANKTON OF THE GULF OF MAINE 87 
Scotia, but in 1914 the neighborhood of Lurcher Shoal proved far less productive 
than the deeper basin near by. 
Were all parts of the gulf equally favorable for the existence and multiplication 
of animal plankton, the catches of the vertical hauls might be expected to vary in 
direct ratio to the depth — that is, to the amount of water filtered by the net — and, 
speaking broadly, there usually is more plankton below any given unit of the sea’s 
surface in moderately deep water (say 50 meters or more) than in very shoal water. 
Notwithstanding the comparative barrenness of the greater part of the coastal zone, 
however, the regional differences in the abundance of plankton in the Gulf of Maine 
do not correspond closely to the depth; nor can they be correlated with the distance 
from the coast, per se, because we have repeatedly found the plankton very plentiful 
in moderate depths both near land, as in Massachusetts Bay, and close in to Cape 
Sable, and as far offshore as Georges and Browns Banks, while, on the other hand, 
some of our deep hauls have proved unproductive in spite of the considerable length 
of the column of water fished through. Such, for example, was the case in the Eastern 
Channel and the neighboring part of the basin in July, 1914. In fact, the vertical 
hauls made in the southeastern deep of the gulf in summer (July 23, 1914, station 
10225, and June 25, 1915, station 10298), have both proved extremely barren, with 
only 30 to 70 cubic centimeters per square meter in spite of the considerable depths of 
the hauls (175 to 260 meters), showing that both in June of 1915 and July of 1914 the 
rich zone was bounded on the east by much less prolific waters. It is on the strength 
of these hauls that I have laid down the demarcation between the two zones on the 
accompanying chart (fig. 38), but the volume of plankton present in the water varies 
so widely from season to season and from year to year that the lines must not be 
drawn too finely in plotting its regional variations, and the future alone can show 
whether it is regularly characteristic of the summer season for such a barren wedge 
to separate the rich waters to the north from the equally prolific shallows of Georges 
and Browns Banks. 
The presence of more than 200 times as much animal plankton beneath each 
square meter of the surface of the sea at the mouth of Massachusetts Bay on July 20, 
1916, as in water nearly twice as deep in the Grand Manan Channel on August 19, 
1912 (only a trace), and the fact that there were 200 cubic centimeters per square 
meter in 85 meters of water on the northeastern edge of Georges Bank on July 24, 
1914, but only 50 cubic centimeters per square meter that same day in the Eastern 
Channel, 15 miles distant, where the depth was 220 meters, illustrate the contrast 
between productive and barren waters. 
Vertical hauls in the Massachusetts Bay region, the only part of the gulf where 
our data warrant even a tentative account of the quantitative fluctuations that take 
place during late summer and autumn, suggest a diminution in the volume of zoo- 
plankton during the late summer followed by an autumnal increase, which was so 
considerable in 1915 that there was over twice as much plankton per square meter 
in water only 80 meters deep by the end of October as we had found at a neighboring 
station in 140 meters depth two months previous. 
