PLANKTON OF THE GULF OF MAINE 
197 
about 1,000 per cubic meter, with 2,300 and 3,700 at two stations at the mouth of 
Massachusetts Bay, these being among the densest aggregations of the species yet 
demonstrable from our vertical hauls. 
In marked contrast to this rich region and to a second center of abundance in 
the eastern basin (1,900 per cubic meter), there was a sparse stock of Calanus along 
the coast of Maine east of Penobscot Bay (40 to 100 per cubic meter) in June, and 
it was only moderately abundant on Browns Bank (120 per cubic meter, station 
10296). 
In the cool year of 1916, when it is probable that the vernal cycle in the lives 
of planktonic animals lagged behind its normal schedule, Calanus was extremely 
plentiful in the Massachusetts Bay region and off Cape Cod in July, as already 
described (p. 195); and while the numbers per square meter fell somewhat short of 
the maximum for May, the numbers per cubic meter — both maximum and average — 
were slightly greater because of the shoalness of the localities where the vertical 
hauls were made. 
Numbers of copepods and Calanus finmarchicus per cubic meter, assuming the latter to average 70 per 
cent of the former, July 19 to 22, 1916 1 
Station 
Depth in 
meters 
Copepods 
per cubic 
meter 
Calanus 
per cubic 
meter 
Station 
Depth in 
meters 
Copepods 
per cubic 
meter 
Calanus 
per cubic 
meter 
10340 
45 
2, 066 
3,312 
1,446 
2,318 
4, 301 
1, 568 1 
10345 
150 
930 
651 
10341 
80 
10346 
62 
2, 987 
2,791 
1 0342 
6, 145 
2,240 
10344 
80 
Average. 
3,113 
2,179 
1 The exact proportions of the several species of copepods have not been determined as yet for these hauls, but preliminary 
examination suggests at least 70 per cent Calanus and probably more. 
The copepod population being confined largely to the deeper layers, as evidenced 
by the comparative poverty of the surface catches, Calanus finmarchicus was evidently 
more densely aggregated locally than even these amounts per cubic meter would 
suggest. For example, the haul at 40 meters (station 10344), with the 1-meter net, 
yielded about 6 liters in 15 minutes, chiefly copepods, and contained upward of 
2.500.000 large Calanus (Bigelow, 1922, p. 136). This compares favorably with 
200.000 in a five-minute haul near Iceland, listed by Paulsen (1906) as one of his 
richest. 
In the daytime the stock of Calanus at, say, the 10 to 30 meter level, becomes 
to some extent enriched by the tendency of this little crustacean to sink when the 
sun is high; at night it is correspondingly impoverished. 
The July hauls for 1916 represent the richest Calanus pasture for mackerel, 
herring, etc., that has come to our notice, and hence may be regarded as containing 
about the maximum number per cubic meter to be expected in any part of the gulf 
at any season, except in years for some reason unusually productive. When and 
where this crustacean food supply is at its best, therefore, a plankton-feeding fish 
finds at least 2,000 Calanus per cubic meter at some level, and probably many more 
at others, for this copepod has often been reported in shoals. On such occasions 
every few mouthfuls of water taken by an adult mackerel, herring, alewife, or shad 
8951—28 14 
