294 DISCOVERY REPORTS 



that Farran (1929) found it in the Terra Nova collections as far south as 77° 30' S near 

 Cape Royds and Cape Evans, and Wolfenden (191 1) found isolated specimens in the 

 Gauss collection as far north as 46° S and one from 3000 m. between Tristan da Cunha 

 and Cape Town. The ' Valdivia ' also found very small numbers in the latitude of Cape 

 Town in the Atlantic and South Indian Oceans (Schmaus and Lehnhofer, 1927). The 

 material obtained by the ' Discovery II ' gives a considerably better picture of the dis- 

 tribution of R. gigas in the Falkland Sector of the Antarctic than elsewhere, since ob- 

 servations in that sector were made in the summer months. The stations around the 

 Antarctic Continent, however, were taken during the winter so that the picture they give 

 is that of the winter distribution of the species. 



HORIZONTAL DISTRIBUTION, SEASON 1931-2 

 Falkland Sector, November to mid-January (Table III «) 



The figures for the lines of equal numerical distribution (Fig. 8) and of equal per- 

 centage distribution (Fig. 9) in the Falkland Sector during the first half of the season 

 193 1-2 allow certain broad generalizations to be made. The figures should be studied in 

 conjunction with the isotherm map (Fig. 5), in which, as already explained, the average 

 temperature for the surface 100 m. has been plotted for every station. 



The area of maximum abundance of R. gigas is seen (Fig. 8) to be an area where the 

 combined hauls (250-100 and loo-o m. together) amounted by estimation to over 

 10,000 individuals. In this area R. gigas amounted to 75-100 per cent of the total 

 copepod catch (Fig. 9). This region of maximum abundance is seen to include the waters 

 of the Drake Passage south of the Antarctic convergence, the western Scotia Sea, and 

 the waters of the South Atlantic Ocean south of the Antarctic convergence lying west, 

 north and north-east of the island of South Georgia. In the Drake Passage the area 

 of maximum abundance extends south of the o and — i-o° isotherms, but in the western 

 Scotia Sea and South Atlantic Ocean it lies always north of the 0° isotherm. The 

 Antarctic convergence forms the northern boundary of this area except at St. 746, 

 which is situated practically upon the convergence itself, and at St. 776, which is also 

 extremely near the convergence. At the latter station 86-5 per cent of the total copepod 

 catch was made up of Rhincalanus, although the actual number of individuals in the 

 combined hauls amounted to less than 10,000 (5325 — see Table III a). 



It is thus seen that the area of dominance and abundance lay in the warmer Antarctic 

 water in the South Atlantic and western Scotia Sea, where the temperature (average for 

 the surface hundred metres) was higher than 0° and lower than 3-0° C. This water 

 constitutes that part of the West Wind Drift current in the Falkland Sector which 

 originates in the Bellingshausen Sea and is known as the Bellingshausen Sea current. 

 In the Drake Passage the area of maximum abundance extended into water from the 

 Bellingshausen Sea having an average temperature less than — i-o° C. (St. 739) and less 

 than — 1-5° C. (Sts. 735 and 737). There are no observations in this particular season to 

 show the distribution of the species in the Bellingshausen Sea itself. 



Within the area of abundance certain regions may be distinguished where the popula- 



