2 S o DISCOVERY REPORTS 



on the ground that the majority of Blue and Fin whales which inhabit the Antarctic in 

 summer move northwards in winter to warmer waters in temperate regions. The fact 

 that the catching of Blue and Fin whales was at one time continued on a small scale 

 through the winter at South Georgia shows that the northward migration does not in- 

 volve the withdrawal of the whole population of these species from the higher latitudes. 



Variation in the fatness of whales is well known as evidence of their migrations. The 

 changes in thickness of the blubber were described by Mackintosh and Wheeler (1929, 

 pp. 363-72), and it was shown that at South Georgia Blue and Fin whales became fatter 

 towards the end of the summer, while at South Africa they become thinner as the winter 

 goes on. The increasing production of oil per Blue whale unit during the Antarctic 

 pelagic whaling season is shown graphically by Bergersen, Lie and Ruud (1939, p. 12), 

 and although this increase might be partly due to the increasing proportion of Fin whales 

 in the catches (see p. 208) it is no doubt largely caused by a real increase in fatness. The 

 argument is, of course, that since whales caught in the Antarctic increase in fatness 

 during the summer season there must be a period in which a corresponding decrease 

 occurs. Whales taken in temperate waters in winter show such a decrease, and since there 

 is abundant food in the Antarctic and little food in the warmer regions it is to be sup- 

 posed that the fat, well-fed whales at the end of the Antarctic summer migrate to the 

 warmer regions where, with little to eat, they lose their fatness and return as thin whales 

 to the Antarctic in early summer. 



For reasons already given (see p. 214) the occurrence of the parasites Pennella and 

 Coronula, and of the pits and scars on the skin, is evidence, though not conclusive 

 proof, of seasonal migrations. 



Most of this evidence has been described by previous authors, but it is assembled here 

 for completeness, and it can leave no doubt that there is a general tendency for Blue and 

 Fin whales to undertake long annual migrations between the Antarctic and temperate or 

 tropical waters, though this is not to say that the Antarctic is completely deserted in 

 winter or the warmer waters in summer. 



Although much is known of the distribution of Blue and Fin whales in the Antarctic 

 in summer, hardly anything is known of their destination when they migrate to the 

 north in winter. They evidently do not concentrate in coastal regions as does the Hump- 

 back, and it does not appear that they are ever seen in large numbers in warmer waters 

 in winter as they are seen in cold waters in summer. It can only be supposed, as Harmer 

 suggests (193 1, p. 135), that they become very much dispersed over an immense area in 

 winter, some perhaps penetrating into tropical waters, many being scattered in the open 

 ocean in subtropical and sub-Antarctic waters, and some staying in the Antarctic without 

 any major journey to the north. If there were any localities, even in the open ocean, to 

 which these species resorted in any large concentrations in winter it is difficult to believe 

 that they would not have been observed from time to time. 



In the Antarctic Blue and Fin whales are more evenly distributed than Humpbacks 

 and do not concentrate in such definite groups. Their distribution, being less clearly 

 defined, is more difficult to elucidate, and the effect of whaling, in so far as it alters the 



