BIGELOW: COAST WATER EXPLORATION OF 1913. 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 may 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 searcity 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. (Foran 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- 
_jcause the calculations take no account of the failure of the net to filter 
ithe water completely. 
| The only species which vied with Calanus finmarchicus in abundance 
in the Gulf of Maine was Pseudocalanus elongatus; though it was far 
(ess important in the economy of the Gulf because of its small size. 
Pseudocalanus outnumbered Calanus on German Bank (Station 
¢ bone and in the northeast corner of the Gulf (Stations 10097, 10098) ; 
ind it was taken in large numbers in every haul of the quantitative net; 
hough Calanus was usually the more abundant of the two. But the 
| 
| 
: 
