282 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 teniporal 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 role in the Gulf of Maine (though there are no local observations bearing on 

 this point) , probably it ranks next to Calanus finmardiicus 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 



