DISCUSSION OF RESULTS i77 



the nine seasons 1922-3 to 1930-1. In these tables numbers which have yielded a 

 resultant value of less than 10 per cent and are thus not represented graphically in 

 Figs. 3-6 are enclosed in brackets. 



DISCUSSION OF RESULTS 

 SOUTH GEORGIA WHALING GROUNDS 



The whaling grounds at South Georgia are visited annually during the southern 

 summer by both Blue and Fin whales. Seasons vary greatly: in some years Fin whales 

 will be taken much more abundantly than Blue, in some years vice verso ; in some years 

 both species are plentiful and in some both are scarce. These marked fluctuations are no 

 doubt mainly dependent on alterations in the environment, and it appears probable that 

 the predominance of one species over another is determined, at least in some measure, 

 by the position of the ice-edge and the temperature of the water. Interesting evidence 

 bearing on this point has recently been published by Sir Sidney Harmer.^ 



Both species, however, have the same objective in visiting the island. They do so m 

 order to make use of the abundant food supplies that are to be found there. And since 

 the food of Blue and Fin whales is the same, and its presence appears to be largely 

 determined by a system of currents which varies but little, it is to be expected that no 

 differences will be found in the distribution of the two species on the whaling grounds. 

 That this is true is shown by Plate XXIII, in which all recorded positions of capture 

 over a series of eight years are incorporated. It will be seen from the charts that the two 

 species are taken over similar areas and that there is a remarkably close agreement in the 

 contours illustrating regions of concentration. 



That the principal whaling grounds lie to the north-east of South Georgia is to be 

 explained on hydrological grounds. It is due to the system of currents which prevails in 

 the neighbourhood of the island. One of the currents, which comes from the Pacific, 

 flows through Drake Passage to the south of Cape Horn, and taking a north-easterly 

 direction passes to the west of South Georgia. As it progresses northwards it comes 

 more and more within the influence of the westerly winds and thus tends to take a more 

 easterly course. The second and more important current is of Weddell Sea origm. It 

 passes round the south-eastern end of South Georgia and then sweeps in a north- 

 westerly direction along the coast. Before, however, it reaches the northern end of the 

 land it meets the first current and the prevailing westerly winds and is reflected back- 

 wards to take a north-easterly course. The direction of the Weddell current is thus 

 largely due to the presence of South Georgia and to the position which the island occupies 

 athwart the region where the two streams converge. 



Euphausia superba, the exclusive food of Blue and Fin whales in the Antarctic, is a 

 pelagic prawn which drifts northwards to South Georgia from higher latitudes, the 



1 Harmer, Southern Whaling, Proc. Linn. Soc. London, 1931, p. 131. 



