PLANKTON OP THE GULP OF MAINE 
209 
The chief value of the foregoing notes on the reproduction of Calanus is their 
demonstration that this copepod is regularly endemic in the gulf just as it is in the 
Gulf of St. Lawrence (Willey, 1919). How far west of Cape Cod Calanus breeds 
in any abundance is still to be determined. Judging from its constant presence 
off southern New England (p. 188) and from the fact that juveniles were numerous 
over the inner part of the shelf off Long Island and off New York on August 1 and 26, 
1916 (stations 10362 and 10396; Bigelow, 1922, p. 143), it is probable that consider- 
able production takes place that far west. The rich catches of Calanus made farther 
south during that summer consisted in the main of very large individuals, which 
apparently did not succeed in reproducing to any extent because young stages were 
scarce or absent west and south of Cape Cod in the following November. 
There is reason to believe that the Calanus stock of the eastern part of the 
Gulf of Maine is recruited to some extent by immigration around Cape Sable from 
more northerly breeding centers. Thus, a swarm of large Calanus with comparatively 
few young stages, in the eastern basin on May 6, 1915 (station 10270), might (so far 
as internal evidence goes) as well have represented an immigration as a late stage 
in a local reproduction cycle, the unmistakable westward extension of the Nova 
Scotian current at the time giving the first alternative an a priori probability which 
our failure to find any great production of young Calanus in this region in April, 
1920, tends to corroborate. The swarm off the southeast slope of Georges Bank in 
March, 1920, had probably drifted thither from the east or northeast. 
At present it is impossible to state how regularly such immigrations into the 
gulf take place, or their precise source, but it is probable that in the maintenance of 
the stock of this copepod existing in the Gulf they are of far less importance than 
local production. 
Such data as are available suggest, furthermore, that the northern and eastern 
parts of the gulf are kept supplied with Calanus chiefly by the dispersal of the swarms 
of young produced in the southwestern side, the general circulation of the gulf 
indicating a general anticlockwise drift eastward along the northward side of Georges 
Bank and thence northward and westward around the gulf. Nor is a drift of this 
sort inherently improbable, for Calanus regularly carries out far more extensive 
involuntary migrations from its chief breeding centers in north European and sub- 
Arctic seas. 
Relationship to temperature and salinity . — Most authors have described C. 
Jinmarchicus as eurythermal, which is certainly true within very wide limits. In the 
Gulf of Maine it occurs regularly over a range of from fractionally above 0° to 20° 
(station 10254, surface, Calanus plentiful). I do not know the highest range in 
which it has ever been found, but on August 30 and 31, 1913, the Grampus took 
occasional specimens (living) in 24.44° on the surface off Delaware Bay, where by 
sinking 20 meters or so it could have found much cooler water of 11 to 12° (Bigelow, 
1915, p. 290). Although apparently it is able to exist in such high temperatures, 
much evidence has been accumulated to the effect that somewhat cooler water offers 
a more favorable environment for it, whether as it effects the growth of the Calanus 
itself, its reproduction, or its food supply. This was unmistakably the case in the 
