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BULLETIN OF THE BUREAU OF FISHERIES 



These observations make it probable that Megancytiphanes deserts the shallow 

 coastal zone as winter draws to its close, in order to avoid the extreme chilling to 

 which this part of the gulf is subject; but data for a single year, and especially for 

 one as cold as 1920, are not enough to settle this point definitely. On the other hand, 

 the great majority of our captures of Meganyctiphanes have been from water colder 

 than 12°, both in the offshore parts of the gulf and on the surface about Eastport 

 and St. Andrews. But off Cape Cod, on August 23, 1914 (station 10256), we found 

 it indifferently on the surface at a temperature as high as 19.5° and in the much 

 cooler (5 to 6°) layers deeper down, and probably the Massachusetts Bay swarm 

 mentioned below (p. 153) was likewise living in water at least as warm as 16°. 



Evidently the highest temperatures that ever obtain in the open waters of the 

 Gulf of Maine are not immediately fatal to Meganyctiphanes, though it is doubtful 

 whether it could long survive water so warm; nor does it always avoid it, although 

 it may cease its upward swimming to do so or sink a few fathoms to escape it once it 

 has come up to the surface. Nevertheless, judging from the distribution of Mega- 

 nyctiphanes in other seas, it is probable that a constant high temperature is not 

 favorable for it, and I think it safe to set 12 to 15° as the upper limit for its per- 

 manent existence, and especially for its reproduction. Within the limits of 3 to 15° 

 it is practically eurythermal in the Gulf of Maine, both horizontally and vertically, 

 and its distribution there is equally independent of local and vertical differences in 

 salinity, for it occurs indifferently over the whole range — that is, from 31 per mille 

 or less to 34 per mille — except perhaps in the very freshest water at the time of 

 the spring freshets. This parallels its distribution in European seas, where it is 

 common in the Skager-Rak in salinities ranging from as low as 28 to 30 per mille to 

 as high as 34 to 35 per mille at different seasons (Kramp, 1913). 



Apparently there is nothing in the physical state of the water over Georges 

 Bank to account for the scarcity or absence of this euphausiid there, nor can a cause 

 be assigned for this apparent anomaly in its distribution until its life history has 

 been traced in more detail. 



The bathymetric distribution of Meganyctiphanes in the Gulf of Maine remains 

 puzzling. Most of our summer records for it in the offshore parts of the gulf have 

 been from deeper than 40 meters or so, and when this shrimp has occurred on the 

 surface at that season it has usually been represented more numerously at some 

 deeper level, a rule Illustrated by two stations in the western basin (August 22 and 23, 

 1914), when the number of Meganyctiphanes taken in the several hauls was as 

 follows : 



Not only have we taken it right down to the bottom of the deepest trough of the 

 guff, but it is only in the lowest strata of the latter that it occurs regularly and in 

 numbers throughout the year, except in the Eastport region. To balance against 



