PLANKTON OF THE GULF 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. 

 finmarcliicus 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 



