THE AGE OF FEMALE BLUE WHALES 



241 



to the tropics. It may well be that some of these are the resting whales, which were so 

 exhausted by lactation that they could not afford the long fasting journey to the tropics, 

 where there is no Euphausia superba, and, staying south, missed the breeding period. 



pelagic data. The season in which I investigated whales on board the ' Southern 

 Princess ' was the last for which we have first-hand information of the catch of lactating 

 whales. In that season, the capture of lactating whales by the Norwegian fleet was 

 prohibited, but a number of lactating whales were taken by British companies, although 

 most gunners disliked to kill nursing mothers. The season was from October 23 to 

 March 29. Of the 180 mature females which I examined in special detail during that 

 time, sixteen or 9 per cent were in active lactation. Sixty-four (35 per cent) were resting, 

 four more had a fresh corpus luteum but no foetus, and ninety-six (54 per cent) were 

 pregnant. The occurrence of the lactating and resting whales was as follows : 



The same suggestion of a longer lacta- 

 tion period is in these figures, but this 

 case is even more likely to be misleading, 

 because the latitude in which these whales 

 were caught is higher (60-66 S) and the 

 mothers who brought their young far 

 south would take even longer in their 

 passage. The high incidence of resting 

 whales in the first part of the season 

 again suggests that they are a distinct class. 



In the data for the last two seasons, 

 1934-5 and 1935-6, the composition of 

 the catch is different, since no lactating 

 whales may now be caught. Occasionally 

 one may be taken in error, but the pro- 

 portion is so small as to be negligible, 

 even if these whales were always recorded 

 in the log books of the factory ships. 

 There are now only two main classes of 

 adult whales in the catch, pregnant and 

 resting. 



60 



60 



(- 

 m 



UJ 



* 40 



u_ 

 O 



< 



20 



TWO FACTORIES 1934-5 

 ONE FACTORY 1932-3 

 S.GEORGIA "1925-31 



OCT 

 Fig. 7 



NOV 



DEC 



JAN 



FEB 



MAR 



. Percentage of resting whales 

 in the catch by months. 



3-2 



