BIGELOW: COAST WATER EXPLORATION OF 1918. 291 



depths of the Gulf of Maine. Calanus was wholly absent in pure 

 Gulf Stream water, as exemplified by Station 10071, and the deeper 

 layers at Stations 10064 and 10076; and it was likewise lacking in the 

 very fresh water at the mouth of Chesapeake Bay. The possibility 

 that the density of the water ma}^ determine the bathymetric distri- 

 bution of copepods, by its effect on flotation, just as is the case with 

 fish eggs, must be taken into account in geographic studies. The 

 Calanus swarms in the Gulf of Maine were living in water of about 

 1.024 to 1.027. The lowest density in which adults were found 

 abundant was 1.0239 (Station 10093, surface) though larval stages 

 swarmed in water of 1.0231 (Station 10085, surface); the highest, for 

 swarms, was about 1.027 in the deeper parts of the Gulf. None 

 of the physical factors just outlined offer an obvious explanation for 

 the scarcity of Calanus in the waters south of New York in July, for 

 the subsurface salinities, temperatures, and densities of many of those 

 stations were well within the range occupied by the species in the Gulf 

 of Maine. What the limiting factor is, is one of the numerous ques- 

 tions raised, but not answered, by our cruise. Most of the specimens 

 were large adults, as was the case in the summer and autumn of 1912. 

 But the catch off Cape Cod on July 9 (Station 10057) was larval stages; 

 and young stages swarmed in Massachusetts Bay during the early 

 spring of 1913. (For an account of the biology of Calanus finmarchicus 

 in Norwegian waters, see Damas, 1905). 



The results of the quantitative hauls give a rough idea of the abso- 

 lute abundance of Calanus in our Gulf (p. 286). Taken at their face 

 value, they show that the numbers of Calanus in a column of water 

 of one square meter cross section varied from 3750 to 88000, being 

 greatest, as the plankton as a whole was richest (p. 237), off Massa- 

 chusetts Bay and over the eastern basin, least in the northeast corner 

 of the Gulf (Station 10098) and German Bank. The average of the 

 hauls for the Gulf as a whole is 28000 per square meter of surface area. 

 But Calanus must have actually been more numerous than this, be- 

 cause the calculations take no account of the failure of the net to filter 

 the water completely. 



The only species which vied with Calanus finmarchicus in abundance 

 in the Gulf of Maine was Pseudocalanus elongatus; though it was far 

 less important in the economy of the Gulf because of its small size. 

 Pseudocalanus outnumbered Calanus on German Bank (Station 

 10095) and in the northeast corner of the Gulf (Stations 10097, 10098) ; 

 and it was taken in large numbers in every haul of the quantitative net; 

 though Calanus was usually the more abundant of the two. But the 



