SEASONAL CHANGES IN THE COMPOSITION OF THE STOCK 



271 



invariably takes place in every season, and there is no doubt that it represents a real 

 change in the species ratio in the whale population. The figures for Sei whales are of 

 doubtful significance for this species does not usually migrate into very cold water, and 

 it is difficult to know whether any substantial number were taken on the normal grounds. 

 Most Humpbacks are taken in December, January and February. A high percentage 

 appears in November 1938, but the actual numbers taken in December and January 

 were higher. It is not clear whether the figures for Sperm whales include some catches 

 outside the normal whaling grounds. 



Table 24. South Georgia catches. Monthly percentage of each species 



Total catch 



Blue 



Fin 



Sei 



Hump- 

 back 



Sperm 



Per cent 



Blue 



Fin 



Sei 



Hump- 

 back 



Sperm 



September 



October 



November 



December 



January 



February 



March 



April 



October 



November 



December 



January 



February 



March 



April 



35 



752 



1 60 1 



1768 



1 29 1 



361 



203 



36 



7 

 131 



35 

 24 



32 

 3 



(b) Recent season, 1938-9 



2-9 



0-7 

 05 

 01 

 03 



i'3 

 46 

 7-5 



04 

 09 

 IS 

 2-3 

 25-4 



39-5 



At South Georgia (Table 24) Blue whales again become scarce towards the end of the 

 season, but there is no steady change in the proportion of Fin whales. The figures in 

 this table are really misleading, for, as Harmer has shown (1931, p. 131), conditions there 

 vary a good deal from year to year. In some whaling seasons the maximum catches of 

 Blue whales precede the maximum catches of Fin whales, while in other seasons the Fin 

 maximum comes first. Harmer found as a general rule that, in those seasons in which the 

 mean September air temperature at South Georgia was less than 32-5° F, the maximum 

 catch of Blue whales preceded that of Fin whales, while, in seasons in which the tem- 

 perature exceeded 32-9° F, the Blue whale maximum was later than that of Fin whales. 

 He suggests that the explanation is that in general the principal concentration of Fin 

 whales lies rather to the north of that of Blue whales (though of course the two species 

 overlap). Thus in a cold season the Blue whale concentration might lie at first in the 

 latitude of South Georgia while the Fin whales were farther north, and as the season 

 advanced both species would move south, and the Fin whale maximum would therefore 

 follow the Blue. In a warmer season the Fin whale maximum would be nearer to the 



