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BULLETIN OF THE BUREAU OF FISHERIES 
regularly endemic there and that the maintenance of the local stock is primarily by 
local reproduction. The seasonal fluctuations in the numerical strength of the stock 
point to breeding as taking place most actively from June until September and to 
the entire gulf as its site. 
Relation to temperature and salinity. — P. elongatus has been taken over a wide 
range of temperature. Judging from its abundance in polar seas, it thrives in temper- 
atures close to the freezing point; but, on the other hand, notwithstanding its north- 
erly distribution (p. 275), it has been found living in the warm Mediterranean and in 
upwards of 20° in the Gulf of Suez. However, the species reaches its maximum 
abundance and frequency in seas and at levels where the water is cooler than 
about 15°. 
In the Gulf of Maine its presence has been definitely established in water as warm 
as 20° (surface, station 10254, August 22, 1914) and 19.56° (surface, station 10256, 
August 23, 1914); but its usual scarcity at the surface during the warmest months 
(pp. 24, 277) and the great preponderance of records (vertical and subsurface horizontal 
hauls) from temperatures below 12 to 15° would seem to set this as the upper limit 
for its optimum environment, even though much warmer water is not fatal either to 
its existence or even to its reproduction — witness its Mediterranean range. If the 
rising temperature of spring is actually the factor which tends to drive Pseudocalanus 
down into the deeper and cooler water in summer, this does not take place until the 
uppermost stratum of water has warmed from its winter minimum to warmer than 
7 to 8°, for Pseudocalanus occurred rather more frequently on the surface in May, 
1920, when the surface temperature averaged about 7.9° at the Albatross stations, 
than in April at an average temperature of about 3.5°. 
Any species living indifferently in the inner Baltic, on the one hand, and in the 
open Atlantic and Mediterranean, on the other, necessarily exists over a much wider 
range of salinity than obtains in the Gulf of Maine. Therefore, it is not likely that 
the details of distribution of Pseudocalanus in the gulf are governed by the local 
and temporal variations in salinity obtaining there, nor does any parallel between 
the two appear from what is known so far. 
Economic importance. — In the English Channel, Lebour (1919, 1919a, and 1920) 
found that Pseudocalanus was, on the whole, the copepod chiefly preyed upon by 
all kinds of larval fishes and young fish fry; and since it may be expected to play the 
same r61e in the Gulf of Maine (though there are no local observations bearing on 
this point) , probably it ranks next to Calanus finmarchicus in its importance in the 
natural economy of the gulf. Granting Pseudocalanus second rank in this respect, it 
must still fall far behind Calanus, not only because its individuals are much smaller 
but because it is seldom as numerous anywhere in the gulf. Thus, Pseudocalanus 
outnumbered Calanus in only eight out of 139 vertical hauls between the longitudes 
of Marthas Vineyard and Cape Sable during the years 1913, 1915, and 1920, and 
equaled it in three others. As a rule there have been from five to ten times as many 
Calanus as Pseudocalanus at any given station. Taking the vertical hauls together 
for all years, for all localities west of Cape Sable, and for all seasons, Pseudocalanus 
has averaged about 11 per cent of the copepods. Assuming the Pseudocalanus to 
