^76 DEl'ARTMENT OF THE NAVAL SERVICE 



noptera borealis. ' On account of the up-and-down movements referred to in the 

 preceding paragraph, it becomes important to note the time of day when the hauls are 

 made. The total quantity of Calanus present in the column of water filtered through 

 the vertical net at a given station is of more practical concern than the quantity at 

 any particular depth. Esterly found that the maximum abundaaice (" plurimum ") 

 at the surface occurred during evening twilight. The surface, in a quiet sea, is prac- 

 tically deserted during the daylight hours, the plurimum between 6 a.m. and 6 p.m. 

 being located at about 200 fathoms. J. I. Peck (1896) found in Buzzards bay that 

 from sunrise to sunset the copepods desert the surface almost completely. The fac- 

 tors which operate in causing this daily rhythm have been analysed in the case of 

 Lahidorera aestiva by G. H. Parker (1902). Other cases have been discussed by J. 

 Loeb (1894). At station 48 of the Michael Sai^s, between the Canary islands and the 

 Azores, on May 31, 1901, Dr. Hjort states that " the tow-net at 40 metres contained 

 a mass of red copepods, which were not observed at the surface during the daytime, 

 but suddenly appeared as soon as it grew dark soon after 6 p.m." 



In addition to the diurnal there are seasonal migrations. Gran (1902) found off 

 the Norwegian coast from Romsdal to Lofoten, females swarming in April and May 

 over the coastal banks. In August and September great quantities of the young stages 

 (II to IV) are found at the surface. In winter Calanus descends into deep water. 

 Gran supposes that the autumnal juniors sink into deep water where they slowly com- 

 plete their growth and rise again to the surface as the spring adults which then spawn, 

 in Norwegian waters. On the other hand the first haul made by the " Princess " on 

 May 11, 1915, between Prince Edward Island and the Magdalen Islands contained 

 both adults and juniors amidst a swarm of Pseu do calanus (see table 1). 



According to Giesbrecht's faunistic observations, the distribution of pelagic 

 copepods does not conform to the oceanic currents although these are factors in their 

 dispersal. Beyond a certain point the distribution of Calanus -finmarchicus does not 

 seem to be determined by ordinary physical factors. In the gulf of Maine this species 

 was taken by the Grampus in water at temperatures ranging from 42° to 76° F., but 

 was most abundant between 42° and 50° F. (5-5° to 10° C). The density of the water 

 in which it was living in swarms varied from 1024 to 1-027. It was wholly absent 

 in pure Gulf Stream water and in the very fresh water at the mouth of Chesapeake 

 Bay. Bigelow adds that none of the physical constants which were determined in his 

 exploration of 1913 will account for " the scarcity of Calanus in the waters south of 

 New York in July, for the subsurface salinities, temperatures, and densities of many 

 of those stations were well within the range occupied by the species in the gulf of 

 Maine. What the limiting factor is, is one of the numerous questions raised, but not 

 answered, hy our cruise." (Bigelow, op. cit. 1915, p. 290-291). That the Gulf Stream 

 is no barrier to C. -finmarchicus in the proper latitude, is shown by the records of 

 Acadia station 16, June 1, 1.45 a.m., where the surface copepod haul contained 82 per 

 cent of this species, the temperature exceeding 12° C, and the salinity 35 per thousand. 



The factor which determines the limit of southern dispersion of C. -finmarchicus 

 is clearly neither a simple physical constant nor a single organic tropism. It can only 

 be explained at present in terms of endemicity, which includes the biological factors 

 of food-supply and propagation. The Calani which swarm in and about the gulf of 

 St, Lawrence have not been brought there by the Labrador current but are endemic in 

 the Canadian waters. This is shown not only by the presence of the different stages 

 but by the occasional capture of spawning females, taken in the act of extruding an 

 egg or before the latter has had time to become detached from the body of the parent. 

 This is not a frequent observation but was noted in several instances, viz.. Princess 

 stations 9 and 17; Acadia stations 3, 35, 65, 66, 88; No. S3 stations 13, 14, 25, 26. 

 Females with spermatophore were seen at Princess station 20; Acadia stations 66, 79, 

 85, 86, 87, 89 ; No. 3S stations 13, 25, 58, 59, 64. 



The endemicity of C. finmarchicus in the gulf of St. Lawrence being thus proved, 

 it remains to consider its habit of assembling in swarms, in other words its gregarious 



