MULTIPAROUS FEMALES 



441 



Table 24. Monthly frequencies of non-pregnant mature females at South Georgia (1927-35) and the 

 estimated cumulative frequencies of ovulations in this class assuming a corpus luteum life of 15 or 20 days. 

 See text for explanation 



100 



D J F 



MONTHS 



O N 



D J 

 MONTHS 

 b 



M 



M 



Text-fig. 48. a, Monthly '% pregnant', South Georgia 1925-31 (full line), pelagic 1932-52 (broken line), b. Monthly 

 frequency of pregnant (full line) and non-pregnant females (broken line) in the South Georgia catches 1927-35. 



recent ovulations (uncorrected for the active life of the corpus luteum), is then obtained as described 

 above (Text-fig. 47), and the number of recent ovulations observed in each month (column (7)) is 

 obtained by applying these percentages to the estimated number of non-pregnant females in the catch. 

 The question of the proportion of lactating whales in the monthly samples is discussed in the next 

 section (p. 448), and it is shown that there are relatively large numbers at South Georgia from 

 December onwards, but that very few enter the pelagic grounds until January or February, having 

 weaned the calf before entering colder waters. Those lactating females which do enter the catches are 

 either about to wean, are weaning, or have just weaned, the calf (see below, p. 445). For present 

 purposes lactating females are, therefore, included in the non-pregnant group. Columns (8) and (10) 

 show the estimated numbers of ovulations on the assumption that the corpus luteum is recognizable 

 as such in females taken on the whaling grounds for 15 or 20 days respectively, and in columns (9) 

 and (11) the cumulative frequencies of recent ovulations are shown. 



If we are correct in postulating that new arrivals to the non-pregnant fin whale female population 

 in the Antarctic ovulate and then enter the true 'resting' state, then the cumulative figures for the 

 number of ovulations should correspond to the build-up of the antarctic population of 'resting 

 females. Unfortunately, we have no data on the actual numbers of animals in the population, but for 

 present purposes we may assume that the monthly catches correspond to the relative abundance in 

 the sea. The catching intensity is probably rather less at the beginning and end of the whaling season, 

 but this does not affect the general argument. In Text-fig. 49 the catch of non-pregnant females is 



15-2 



