DISCUSSION OF RESULTS i79 



there is a definite correlation between the mean temperature of the air at South Georgia 

 in September and the order in which Blue and Fin whales reach their maxima in the 

 following season. With low temperatures the Blue whale reaches its maximum first and 

 with high temperatures the Fin. Working on these data he has been able to classify the 

 seasons into three groups, but this grouping does not agree with that based on whale 

 movements. The two exceptional seasons as regards movement do not appear in the 

 same groups ; 1924-5, with low September temperature, falls in Group I, and 1925 with 

 high September temperature in Group III. This lack of agreement is perhaps to have 

 been anticipated, for the relation which Sir Sidney Harmer has discovered is between 

 events which occur in the early part of the season and it may well be that whale move- 

 ments in the latter part are due to other causes. 



Another feature of interest in the South Georgia returns is the evidence of the great 

 extension of the whaling grounds in recent years. Since whaling began in 1904 the 

 whaling companies have made constant improvements in their whale-catchers, and with 

 increased size and horse-power and greater speed they have been able to work farther 

 afield. 



If the South Georgia data for the eight seasons are divided into two four-year periods 

 they yield the results shown in Plate XXIV. Results for Fin and Blue whales are charted 

 separately, and as will be seen they show a very close correspondence. The area covered 

 by the whale-catchers during seasons 1923-4 to 1926-7 is indicated by a fine dotted 

 line, while that for seasons 1927-8 to 1930-1 is limited by a continuous line. The position 

 of the main concentration in each of the four-year periods is also shown. 



It will be noticed at once that in each of the species the centre of concentration has 

 shifted some 40 or 50 miles to the east, but with the great variation between individual 

 seasons and the comparatively short periods involved, there must be some uncertainty 

 as to the significance of this movement. A change in the centres of concentration may 

 clearly be brought about by a change in the position of the shoals of Euphausians on 

 which the whales feed, and this in its turn will probably be dependent on changes in the 

 hydrology of the area. For the later seasons some information on these subjects will be 

 available when the surveys made by the research ships have been worked up. If, 

 however, average conditions in the environment were comparable in the two four-year 

 periods, it would appear that the alteration in the centres of concentration can only be 

 explained as a response to intensive whaling : the whales have been scared and no longer 

 venture so close to the island. 



The considerable extension of the grounds during the recent four-year period, and 

 the fact that with the same number of whale-catchers fewer whales have been taken, 

 lends support to the generally held opinion that whales are now less abundant than 

 formerly. The data for the two periods may be summarized as shown in Table IX. 



The figures indicate heavy depletion of the stock of Fin whales and still heavier 

 depletion of Blue whales; but in view of the short periods which are considered and the 

 great seasonal fluctuations in abundance, they cannot be regarded as reliable and calcula- 

 tions derived from them can only be misleading. The greatest catch of Fin whales ever 



