262 



BULLETIN OF THE BUREAU OF FISHERIES 



These average numbers of this copepod per square meter, calculated from the 

 vertical hauls, do not suggest that the strata of water below 150 to 200 meters added 

 appreciably to the catches, although not enough deep hauls were made for a positive 

 assertion. 



Local breeding and immigration. — No direct observations have been made on 

 whether or to what extent M. lucens spawns in the Gulf of Maine. Consequently, its 

 geographic and seasonal distribution is the only basis on which to judge whether 

 the local stock is chiefly the result of local reproduction or depends upon immigration 

 from richer centers of propagation for its maintenance. The regularity of occur- 

 rence and comparative abundance of the species within the gulf is a strong argument 

 that it is regularly native there. Its regularly increasing numbers during the spring 

 and the pronounced augmentation in its numerical strength in September and 

 October likewise point to vernal and autumnal waves of propagation. However, 

 no definite areas of abundance which might be looked upon as local centers of repro- 

 duction have yet been demonstrated for this species in the gulf, notwithstanding the 

 large numbers of locality records and counts of actual abundance which the Grampus, 

 Albatross, and Halcyon cruises have afforded. The fact that it has been found most 

 regularly in the eastern and southern parts of the gulf points to a certain amount of 

 immigration via the two channels and across Browns Bank from the continental 

 shelf off Nova Scotia, where the Canadian fisheries expedition found it widespread 

 (Willey, 1919). 



Until its status is better understood in the gulf the latter may be looked on as a 

 regular and important breeding center for it, but with the local stock augmented by 

 immigration. 



Relationship to physical conditions. — In other seas M. lucens has been found over 

 a wide range of temperatures from 4.83 to 20.5°, usually upwards of 5.5°; and 

 in salinities ranging from 28.1 to 35.4 per mille, most commonly in 33.3 to 35.3 per 

 mille (Farran, 1910; Esterly, 1912). The Gulf of Maine records bring the lower 

 limit of temperature down to 0.33 to 0.78° (station 20062, March 5, 1920); and its 

 presence on the surface in the coastal waters of the gulf in late winter and early 



