208 BULLETIN OF THE BUREAU OF FISHERIES 



by Dr. C. B. Wilson (table, p. 305), but the fact that no decided multiplication of the 

 later stages of Calanus takes place during late winter (p. 39) suggests that these 

 belonged to some other species of copepod and that C. finmarchicus breeds little, if 

 at all, in the gulf from September or October until the following April. 



In north European seas generally, where the biology of this copepod has attracted 

 the attention it deserves, it is primarily a spring or summer breeder, the spawn- 

 ing season commencing soon after vernal warming of the water is appreciable and 

 consequently varying with latitude and with oceanic conditions. Thus Gran 

 (1902) found it in full breeding condition on the northwestern coast of Norway 

 (latitude about 67° N.) in April and May; Damas (1905) in June in the Norwegian 

 sea, where the Arctic and Atlantic currents meet, and in May and June around the 

 Faroes. Paulsen (1906) states that the reproductive season south of Iceland lasts 

 from March into June; Damas and Koefoed (1907) describe this copepod as spawning 

 in late June along Norway and in the fjords of Spitzbergen; while With (1915) found 

 it in breeding condition in June in Denmark Strait, in May south of Iceland, in June 

 and July off West Greenland, and as late as the last days of July off eastern Greenland. 

 Thus With justly interprets the term "spring," as descriptive of the chief breeding 

 period of C. finmarchicus, to mean the period at which the waters reach a certain 

 temperature and salinity, and which varies according to the latitude from March 

 (February?) to August (east Greenland). The AprU to June spawning in the Gulf 

 of Maine thus parallels the breeding period of this copepod in the southern parts 

 of the northeastern Atlantic area. 



Although most European authors have credited C. finmarchicus with one com- 

 paratively brief period of reproduction annually, Paulsen (1906), with whom With 

 (1915) agrees, has pointed out that it probably breeds to some extent at other seasons 

 also in Norwegian and Icelandic waters, just as it certainly does in the Gulf of Maine, 

 because adults of both sexes have been found at other times of year almost every- 

 where in northern seas where towing has been carried out at appropriate depths. 



If it proves characteristic of C. finmarchicus to have two distinct periods of 

 active reproduction in the Gulf of Maine — a major in spring and a minor in autumn — 

 as a preliminary study of our samples suggests, and only one in north European 

 and Arctic seas, the difference may simply be one of latitude, the first spawning 

 occurring so early in the year in the gulf and autumnal cooling commencing so late 

 that there is opportunity for a part of the product of the spring hatch to mature and 

 breed before the temperature of the water falls too low for sexual development. 

 Thus, it is probable that for most of the stock breeding is an annual event and the 

 individuals survive for a year; for others it is biennial, with the autumn hatch passing 

 the winter in the late postlarval stages, as Paulsen (1906) suggests, and enough 

 irregular reproduction taking place at any time from early spring until well into the 

 autumn to maintain the variety of stages in development that have been seen though- 

 out the year. More intensive study of the Gulf of Maine samples may be expected 

 to throw light on this question that would be important not only as bearing on the 

 life history of the species but with regard to the natural economy of the gulf, of 

 which C. finmarchicus is the most important planktonic inhabitant. 



