276 



DISCOVERY REPORTS 



make the following very interesting remarks regarding the whale food of this South 

 Georgia season of 1925-6, giving independent confirmation of our plankton results: 



Plenty of large krill were present in October and the first part of November, but they became 

 scarcer later in November and in the first part of December. No whales were examined in the second 

 half of December, but in January the large krill appear to have been suddenly replaced by a smaller 

 type, scarce at first (unless the whales had difficulty in finding it) and then eaten in fair quantities. 

 This krill seems to have become most plentiful in the earlier part of March. It is an interesting fact 

 that the new type of krill which appeared in January was accompanied by a striking change in the 

 whale population round South Georgia, for whales were very scarce during October, November and 

 December, especially during December. But at about the new year immense numbers of Fin whales 

 appeared. They were found first about 70 miles from the island and seemed to be finding very little 

 food. Later they came closer to the coast and larger quantities of food were found in their stomachs. 



EUPHAUSI/I 



SUPERBA 



FIN WHALES 



BLUE WHALES 



CD 



Fig. 143. Euphausia superba and whale distribution in March 1926 (whale distribution from 



Kemp and Bennett, 1932). 



Few as these plankton observations are, combined with the observations of Mack- 

 intosh and Wheeler just quoted, they suggest strongly that the movements of the 

 whales during their sojourn south are very intimately bound up with the distribution of 

 their food. These conclusions are found to be strengthened by considerations to be 

 discussed in the next section. 



A FURTHER CONSIDERATION OF THE PLANKTON AND THE 



WHALE FISHERIES, WITH AN INTRODUCTION TO THE 



HYPOTHESIS OF ANIMAL EXCLUSION 



It is now desirable to seek an explanation for the distribution of the Euphausia 

 superba. At first temperature suggests itself. We know that they are cold-water forms, 

 and we find them in the December-January survey situated off the north-east coast in 

 water which is colder than that on the south-western side, where the Bellingshausen Sea 

 current has the greater influence. Yet in March 1926, when they were concentrated in 

 such large numbers against the coast, the temperature of the water they were in had an 

 average for the top 50 m. of 2-6° C, which is greater than that found at any part, even 

 off the western coast, during the December-January survey 1926-7. Further, in March 

 the temperatures are higher at the stations against the coast than they are farther out in 



