PLANKTON OF THE GULF OF MAINE 
199 
mately 300 per cubic meter, paralleling the calculations for August as closely as 
could be expected with an animal distributed so irregularly. 
Numbers of C alarms finmarchicus per cubic meter, September and October, 1915 
Station 
Date 
Depth in 
meters 
Number 
Station 
Date 
Depth in 
meters 
Number 
10309 
Sept. 1 
200-0 
692 
10324 
Oct. 1 
150-0 
225 
10310 
190-0 
482 
10325... 
Oct. 4 
175-0 
634 
10311 
60-0 
205 
10326 
...do 
145-0 
325 
10315 
Sept. 7 
80-0 
264 
10327 
Oct. 9 
60-0 
126 
10316 
Sept. 11 
60-0 
265 
10328 
do 
60-0 
237 
10318 
Sept. 16 
70-0 
63 
10329 
...do 
60-0 
245 
10319.... 
Sept. 20 
35-0 
380 
10336 
Oct. 26 
50-0 
2,050 
10320 
Sept. 29 
70-0 
273 
10338. 
Oct. 27 
80-0 
1, 528 
10321 
40-0 
170 
10339 
...do 
75-0 
343 
10323 
Oet. 1 
80-0 
288 
Six stations between Massachusetts Bay and the mouth of the Grand Manan 
channel gave about the same average (298) for the first week of October, with but 
little variation from station to station (see table above), evidence that, as judged 
by the number per cubic meter — that is, the density of aggregation and availability 
for fishes — Calanus finmarchicus was distributed with comparative uniformity over 
the inner parts of the gulf during the late summer and early autumn of 1915, a year 
probably fairly representative. Vertical hauls off Cape Cod and in Massachusetts 
Bay on the 26th and 27th of the month yielded it in much larger numbers, rivaling 
the denser communities of the species in spring and early summer. 
We have no data on this subject for the months of November, December, or 
January, but the catches of the horizontal nets, at depths of 15 to 240 meters during 
the cruise of December to January, 1920-1921, were so small that Calanus must 
then have been distributed very sparsely, indeed, and probably in no greater numbers 
per cubic meter than in March (if as great), judging from the volumes of the catches 
of the horizontal hauls, which consisted chiefly of copepods (see table, p. 304, for 
percentages of Calanus). Thus the whole Gulf of Maine supports a much sparser 
community of Calanus in winter and until May than it does from late spring to 
October, with the maximum density of aggregation for this copepod falling from May 
to July, the seasonal fluctuations in this respect paralleling those of the actual 
numerical strength of the local stock. 
Percentage of occurrence. — The degree to which Calanus finmarchicus predomi- 
nates over all other copepods in the Gulf of Maine basin may best be illustrated by the 
percentages of this species in the total catches of copepods. The vertical hauls of 1915 
1920, and 1921, combined, averaged about 55 per cent C. finmarchicus, inclusion of the 
surface hauls for the spring of 1920 and the horizontals made during the summers of 
1912 and 1914 bringing theprecentage up to about 60. Furthermore, C. finmarchicus 
is the only copepod that has occurred at every tow-net station in all parts of the gulf 
at all seasons and in almost every haul, vertical or horizontal, and the only one that 
we have ever taken in 100 per cent purity. The three instances of this among the 
surface tows for 1920 (stations 20100, 20111, and 20112, see table, p. 303) are not 
especially significant, the total catch being so small in each case that other less 
common species occurring side by side with Calanus might easily have been missed by 
the net. 
