314 



DISCOVERY REPORTS 



than the season 1932-3, and this has been suggested as a possible explanation of the late 

 ascent of Rhincalaniis to the surface in the former season. We now see that this same 

 cause may account for the difference in the composition of the copepod fauna generally 

 at the beginning of the second season of the commission. The higher proportion of cold- 

 water Weddell Sea species at St. 1029, however, may be accounted for by the fact that 

 St. 1029 w^s taken in the tongue of Weddell Sea water which pushes northwards west 

 of South Georgia towards the Falklands (Fig. 6), while St. 788, in December 1931, was 

 taken in the Bellingshausen Sea current. St. 1066, taken in the middle of December 1932 

 near the western end of South Georgia, and the three stations, 1083, 1085 and 1088 

 (Fig. 2fl), taken at the end of that month between South Georgia and the South 

 Orkneys, seem to show that the proportion of R. gigas increased in the copepod fauna 

 towards mid-summer in the region west and south-west of South Georgia. This is 

 indicated in Fig. 15 by a repetition, farther east, of the 75 per cent line. A comparison of 

 the isotherm charts for the first and second halves of the season 1932-3 (Figs. 6, 7) 

 reveals a southward and eastward movement of the isotherm lines in this region which 

 would, no doubt, be responsible for an increase in the proportion of R. gigas in the 

 fauna and a corresponding reduction in the proportion of cold water species character- 

 istic of the Weddell Sea. 



VERTICAL RANGE AND DIURNAL VARIATION 



There is no evidence from the hauls under consideration as to the depths below the 

 250-m. line to which Rhincalarms may extend. Hardy and Gunther (1935, p. 141), how- 

 ever, write of this species during the summer months: " It was most abundant between 

 50 and 250 m. and was not taken at levels below 750 m." We have seen, however, that 

 the area of abundance of the species almost certainly descends below 250 m. during the 

 winter, and Mackintosh (1935) has shown that the winter level of the species lies be- 

 tween 500 and 1000 m. Schmaus and Lehnhofer (1927, table c) record the species in a 

 vertical haul in the South Indian Ocean between 1900 and 2500 m.^ 



The hauls which form the subject of this paper were taken in a great many different 

 places and at a great many different times and do not provide evidence as to the vertical 

 diurnal movements of R. gigas. Hardy and Gunther (1935, p. 241, fig. 109) have, how- 



■'■ Since the above was written a series of hauls was taken with the 70 cm. silk net towed obliquely 

 at various depths at several stations along the ice edge south of the Indian Ocean during November and 

 December 1935. The catches of Rhincalaniis gigas taken in these hauls are tabulated below. 



