164 
BULLETIN OF THE BUREAU OF FISHERIES 
The last of these records is especially instructive, because there were very few, 
if any, Euthemisto in the icy water below the surface at that station. The autumnal 
augmentation of the stock of Euthemisto in the coastal belt of the gulf likewise 
takes place in comparatively high temperatures (e. g., 7 to 11° on October 26 and 27, 
1915, in Massachusetts Bay, stations 10337 to 10339), and our largest November 
catch was on the surface in water of about 10.3° (station 10404). Thus, whether 
or not the relation be a causal one (and this is not safe to postulate, in view of the 
wide distribution of Euthemisto in northern seas), the maximum abundance of 
Euthemisto in the Gulf of Maine coincides with rather high temperature, both in 
season and in the depth at which it congregates, corroborating Le Danois’s (1921) 
observation that off the French coast E. bispinosa is common only in water as warm 
as 14°. The adults, however, whether of compressa or of bispinosa, certainly show 
no tendency to accumulate in the warmest waters of the gulf, which they could 
easily reach by swimming upward for a few meters. On the contrary, Avhen they 
have been found in any number on the surface it has been at times and places where 
the water was at least no warmer than 15°. Only once have we found large Euthe- 
misto in any number at a temperature higher than 14°. 
For the adult, then, the optimum range of temperature in the Gulf of Maine 
is from 4° to about 12°. We have no evidence that any considerable reproduction of 
Euthemisto takes place in the gulf in temperatures lower than 5° or higher than 12 
to 14°, but the fact that we towed occasional very small specimens in February, 
March, and April, 1920, both off Massachusetts Bay, in the western basin, near 
Cape Sable, on Browns Bank, and on the southwest part of Georges Bank (stations 
20045, 20048, 20050, 20072, and 20104), proves that a certain amount of breeding 
takes place in water as cold as 2 to 3°. The larvae, however, are most often abun- 
dant in considerably warmer water, thanks to the fact that summer is the chief 
breeding season, and to their habit of rising to the surface. Here, again, we hesitate 
to assume any causal connection between temperature and the depth which they 
seek, it being as likely that their tendency to congregate at the warmest level is 
due to some quite different cause; such, for example, as the available supply of 
food, the density of the water, or the influence of sunlight. 
Within the Gulf of Maine Euthemisto is usually most numerous in compara- 
tively high salinities, say, upwards of 32.5, per mile, and while we have made very rich 
catches in water as little saline as 31.6 per mille along the Nova Scotia coast, this is 
the lowest salinity in which we have found it in any numbers. Hence, 31.5 per mile 
may be set arbitrarily as the lower limit to its common occurrence in the Gulf of 
Maine. When the superficial layers of the coastal zone of the gulf are fresher than 
this — that is, throughout the period of spring freshets and in early summer — Euthe- 
misto is usually rare there, if not absent; but it would be no surprise to meet excep- 
tions to this rule, for Euthemisto has been found swarming off the English coast in 
water of only 30.26 per mille (Tesch, 1911). 
It is questionable whether high salinities ever act as a barrier to the migrations 
of Euthemisto in the one direction as low salinities do in the other. It certainly 
occurs regularly in water as saline as 35 per mille in the eastern North Atlantic, 
and while it is not a characteristic inhabitant of salter seas (the highest salinity 
we have actually found it in was about 35.2 per mille (Bigelow, 1915, p. 283) ) it is 
