PLANKTON OF THE GULF OF MAINE 
203 
Date 
March. 
April... 
May... 
Percent- 
Percent- 
age in 
age in 
surface 
vertical 
hauls 
hauls 
53 
58 
63 
57 
76 
80 
It is probable that a certain number of C. finmarchicus exist right down to the 
bottom of the trough of the gulf in spring, as they do in summer, though no direct 
proof of this is yet at hand. However, were it as plentiful below, say, 175 meters 
as it is above that level, the deepest vertical hauls — that is, those filtering the longest 
columns of water — would on the average have yielded the largest catches of Calanus, 
which was not the case. Actually, the average numbers (about 11,000 per square 
meter) taken in 15 vertical hauls from depths of 200 to 340 meters in the basin, and 
in one off the southeastern face of Georges Bank from 1,000 meters, 3 during Feb- 
ruary, March, and April, 1920, were less than the yields of 20 shoaler vertical hauls 
from depths of 100 to 175 meters (average approximately 18,000 O. finmarchicus 
per square meter) — evidence that there were not enough Calanus below 175 to 200 
meters to add appreciably to the catches. The two richest catches for March and 
April 4 were in hauls from depths of only 150 and 125 meters, respectively. 
With the increasing intensity of the sunlight and progressive warming of the 
water which accompany the advance of the season, the surface stratum evidently 
becomes less favorable for Calanus, for in summer it is usually decidedly scarce or 
even wanting in the surface hauls, even at localities where it swarms a few meters 
down; but at other summer stations it has been taken in abundance at the surface. 
I have already pointed out (Bigelow, 1915, p. 290) that its absence on the surface 
in the regions where it swarms in deeper water is not caused altogether by sunlight, 
for while it probably does tend to descend during the most brilliantly illuminated 
hours, on several occasions we have made rich catches on the surface when the sun 
was high in the sky. Such was the case off the entrance to Gloucester harbor on 
July 22, 1912 (station 10012), when nearly a liter was taken in the 4-foot net on the 
surface at about 3 p. m. Again, on August 14, 1914 (station 10251), we made a 
rich surface catch of Calanus at about 2 p. m. off Cape Elizabeth; in July, 1916, a 
month when C. finmarchicus was notably abundant, surface hauls yielded considerable 
numbers off Cape Cod at 4 p. m. (station 10345), and off Marthas Vineyard at 5 
p. m. (station 10351). Willey (1919, p. 181) records the presence of this copepod 
in abundance on the surface in the Bay of Fundy between 3 and 4 p. m. under a 
bright sun; but, as he further remarks, this is unusual. Willey suggests that in the 
Bay of Fundy the active stirring of the water by tidal currents may be instrumental 
in bringing the Calanus up at an hour when they ordinarily shun the surface, an 
explanation that may apply to the particular case in point but not to the other in- 
stances just mentioned, which were in regions of weak vertical circulation and cer- 
tainly not of upwelling. 
3 This station touched the swarm of Calanus already described for that location. 
1 103,300 and 78,000 per square meter, stations 20068 (southeast slope of Georges Bank, Mar. 12) and 20105 (Northern Channel, 
Apr. 15, 1920, station 20078L 
