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, when 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 larvse, 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 



