SEASONAL CHANGES IN THE COMPOSITION OF THE STOCK 



277 



Georgia suggest that some of the larger whales return (or small whales move elsewhere) 

 at the end of the season, but reliable inferences cannot be drawn from such details unless 

 they can be shown, with adequate data, to be regular features in a series of whaling 

 seasons. Table 26 cannot give more than a rough indication of the changes which take 

 place, especially as the figures are a combination of several seasons which do not always 

 cover quite the same period of months. The fact that there is usually a sharp fall in the 

 average lengths in the last month of the season may result from a scarcity of whales 

 (which would restrict selection of the larger ones), as much as from a real fall in the 

 average length in the population. 



THE MONTHLY PERCENTAGE OF PREGNANT FEMALES 



There is a marked change in the summer season in the percentage of adult females 

 which are pregnant. Mackintosh and Wheeler (1929, p. 460) noted a higher percentage 

 of pregnant females in the early part of the South Georgia season than in the later 

 months, and Laurie's data from pelagic grounds (1937, p. 242) show the same effect. 

 The extent of the change from month to month can be seen in Table 27. The Antarctic 



Table 27. Percentage of adult females pregnant 



pelagic figures are based mainly on collections of ovaries made on various parts of the 

 pelagic whaling grounds in the seasons 1934-5 to I 93^~9- (They are derived only from 

 a preliminary analysis of the data on ovaries and may subsequently need some slight 

 adjustment. To this extent the table is a provisional one and is intended only to show 

 that there is a marked change in the monthly percentages.) The pelagic figures also 

 include the whales examined by Laurie in 1932-3, Ommanney in 1939-40 and Crimp 

 in 1939-40 and 1940-1. The columns headed 'No.' show the total number of mature 

 ovaries or the total number of adult females examined for pregnancy. The percentage 

 pregnant is calculated on the assumption that when the ovaries provide the only evi- 

 dence, the presence of a functional corpus luteum indicates that the whale was pregnant. 



