152 
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: 
Station 
Depth in 
meters 
Number 
of speci- 
mens 
Station 
Depth in 
meters 
Number 
of speci- 
mens 
10254 
0 
13 
10256 
0 
8 
45-0 
38 
45-0 
35 
225-0 
50 
Not only have we taken it right down to the bottom of the deepest trough of the 
gulf, 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 
