296 DISCOVERY REPORTS 



Sei, and Humpback whales slightly more males are born and survive than females. 

 There are some persistent local variations, notably in Humpbacks, which show a con- 

 siderable excess of females in the Antarctic and males in the tropical catches. 



19. In the course of the summer season in the Antarctic some important changes take 

 place in the composition of the whale population. On the pelagic whaling grounds there 

 is always a marked fall in the proportion of Blue, and a corresponding rise in the pro- 

 portion of Fin whales as the season goes on ; but at South Georgia the maximum catches 

 of Blue whales sometimes precede and sometimes follow the maximum catches of Fin 

 whales. The sex ratio fluctuates a little but does not appear to undergo any important 

 change. There is a higher proportion of young and immature whales in the late summer 

 than in the early summer. This change is not very marked on the pelagic grounds, but 

 is more noticeable at South Georgia. As the summer advances there is a marked decline 

 in the percentage of adult females pregnant. 



20. Changes in the ratio of species in the catches, in the average length, and in the 

 percentage immature all indicate a significant depletion of the stock of Blue whales. 

 There seem to be no obvious signs as yet of any serious depletion of the Fin-whale 

 stock, but statistics of catches show that Humpbacks have been severely depleted at least 

 in certain regions. Whale marking indicates that the fraction of the stock of each species 

 removed by hunting is greater in Blue than in Fin whales, and greater in Humpback 

 than in Blue whales. 



21. Several possible methods of calculating the absolute magnitude of the stock are 

 discussed, and it is thought that when more precise information on the habits and 

 distribution of whales is available some useful approximation might be reached. 



22. Reasons are given for supposing that less damage is done to the stock by the 

 killing of Fin than Blue whales, males than females, large and old than small and im- 

 mature whales, resting than pregnant females, and pregnant than lactating females. 

 This leads to the conclusion that although the stock must be more affected by the 

 Antarctic industry, owing to the large numbers of whales killed, whaling in the winter 

 season in temperate and tropical coastal waters must be more damaging in proportion 

 to the products obtained ; and the tropical Humpback fishery is probably more harmful 

 than the mixed catches at such centres as Durban and Saldanha Bay. 



23. From the point of view of the stock whaling on the Antarctic pelagic grounds is 

 probably more economical in the late than in the early summer months, but at South 

 Georgia it is difficult to say whether there is much difference. 



24. The institution of sanctuaries as a means of checking the depletion of the stock 

 is discussed, and it is suggested that reserves of whales could be maintained if a con- 

 siderable area in the Antarctic is closed to whaling. 



25. It is hoped that in due course the effect on the stock of the reduction of whaling 

 in war time can in some way be measured. 



