DISCUSSION OF RESULTS 185 



Examination of the data for individual seasons, illustrated for Fin whales in Plates 

 XXV to XXXII and for Blue whales in Plates XXXIII to XXXIX, shows that there is 

 very great variation in the position of the main concentrations, and it is by no means 

 easy to ascertain the normal movements of the schools. Two points, however, seem 

 tolerably evident. It appears (i) that the whales first appear in the northern or north- 

 eastern parts of the area, and in the earliest months of the season are found either in the 

 neighbourhood of Smith Island or off King George Island, and (ii) that at the extreme 

 end of the season there is frequently a very close concentration in Bransfield Strait. In 

 the middle of the season the concentrations show great variation and they are sometimes 

 well to the south of these positions. 



These facts, which appear on the whole to be warranted by the data, find their most 

 simple explanation in the theory that the whales arrive on the grounds from the north or 

 north-east, pass along the coast to the south-west and at the end of the season return 

 towards the north-east. The data bearing on this theory can best be examined by in- 

 corporating all the returns for each month in a single chart : this has been done for Fin 

 whales in Plate XLI and for Blue whales in Plate XLII. 



Considering first the Blue whales, it will be seen that the species arrives on the grounds 

 in November, 1 increases in number in December, and that by January the concentra- 

 tions have shifted decisively towards the south-west. In February and March the whales 

 remain rather widely dispersed over the same area, but in April there is a heavy con- 

 centration in Bransfield Strait. 



The monthly aggregates for Fin whales (Plate XLI) are similar to those for Blue; but 

 the species arrives later at the South Shetlands, not appearing in any numbers until 

 December, and the schools do not move so far south as those of the related species. In 

 April there is the same heavy concentration in Bransfield Strait. 



The Blue whale is known to go farther south than the Fin ; it is most plentiful in the 

 neighbourhood of pack-ice and the distance that it travels on its southern migration is 

 no doubt determined by the latitude of the ice-edge — a factor which varies greatly from 

 season to season. In some years therefore, when the pack-ice is well to the north, Blue 

 whales may be expected to remain in the South Shetland area, whereas in others, with 

 the ice-edge far to the south, the majority of them may pass through the grounds and for 

 a time will be beyond the reach of the whalers. The movements of Fin whales are also 

 in all probability determined in some measure by the position of the ice-edge ; but since 

 the normal distribution of this species lies a little to the north of that of the Blue, the Fin 

 whales will less often penetrate beyond the limits of the whaling area. That such a 

 movement as this can actually occur appears to be indicated by events which occurred in 

 the 1925-6 season. The statistics of South Shetland whaling published by Harmer' show 

 that in this season the monthly catches of both Blue and Fin whales yield a conspicuously 

 bimodal graph, with peaks in December and April for Blue whales and in January and 



1 In some seasons Blue whales have been taken in October, but the numbers of recorded positions are so 

 few that this month has not been included in Plate XLII. 



- Harmer, Southern Whaling, Proc. Linn. Soc. London, 1931, pp. 114, 159, graph 4. 



