,8^ DISCOVERY REPORTS 



During the middle months of the season the directional data, though giving a general 

 movement between north-east and south-east, show great variation, and frequently 

 there are marked differences between the two species. Seasons 1924-5 and 1925-6, 

 which were exceptional as regards distribution, do not differ conspicuously in recorded 

 directions, but in 1925-6 a regular north-easterly movement for both species is more 

 clearly shown than in any other season. In the last months of the season a reversal of the 

 general easterly trend is sometimes found. In March and April of the 1923-4 season 

 there is a marked westerly movement of both Blue and Fin whales. A similar change in 

 direction is also seen in the Fin whales returns for the later months of 1927-8, 1928-9 

 and 1930-1 ; for these months the Blue whale data are for the most part inadequate, and 

 it is not possible to compare the two species. 



SOUTH SHETLAND WHALING GROUNDS 



The area covered by the South Shetland whalers, as will be seen from Plate XL, is 

 very large, extending from the east and south of Clarence Island, through Bransfield 

 Strait and south-west to the Biscoe Archipelago. The two charts in this plate incorporate 

 all recorded positions for Blue and Fin whales over a series of eight seasons, and it will 

 be seen that they give the same result as those from the South Georgia grounds : the 

 distribution of the two species is closely similar and the centres of concentration occur in 

 the same places. The two chief concentrations are at the northern and southern ends of 

 Bransfield Strait, one east-south-east of King George Island and one south of Deception 

 Island. There are also smaller concentrations to the west of Smith Island and north- 

 west of Antwerp Island. 



It is to be noted that the two main concentrations are not found throughout the 

 duration of the season. The concentration off King George Island is for the most part 

 found in the opening months of the season, while that near Deception Island usually 

 occurs at its end. 



In discussing the South Georgia results we were able to show that the position of the 

 main concentration of whales may be explained by the hydrological conditions which 

 prevail in the neighbourhood of the island and the accumulations of whale food which 

 result from them. It is more difficult to account for the South Shetland concentrations 

 on these lines. The main current in this area runs in a north-easterly direction from the 

 Bellingshausen Sea through Drake Passage. One branch of this current enters Brans- 

 field Strait north of Brabant Island and flows with increased speed along the northern 

 side of the strait. On the southern side a weaker reverse current is found, and this 

 comes from the Weddell Sea and flows round Joinville Island to take a south-westerly 

 direction. Euphausians, both adult and young, have sometimes been found in abundance 

 in the strait and some of the shoals may be of Weddell Sea origin. Conditions in the 

 strait, both as regards plankton and hydrology, are very complex, and until the data 

 obtained by the research ships has been fully worked up, no complete explanation of the 

 problem can be attempted. 



