266 DISCOVERY REPORTS 



It will be seen that the average length falls off year by year with a particularly sharp drop 



of nearly 2 ft. in 1934-5. 



Not only has the average length of the catch fallen, but it has reached a critical point. 

 It has been shown that apparently newly mature whales appear in the Antarctic catch at 

 lengths of 78-81 ft. The whales taken in 1934-5 averaged just about the mean of these 

 lengths. On the whole, then, Blue females taken in 1934-5 were newly mature. Not 

 having had time to reproduce, they were killed at the outset of their reproductive 

 careers. Actually, of course, the catch is composed of mature and immature whales, 

 but the relative quantities are such that the net result is as described above. 



I wish to repeat the warning I gave in Nature that the consequences of continued 

 intensive fishing under these conditions cannot fail to have a disastrous effect on the 

 future of the stock. When killing has reached the point at which recruitment, already 

 dangerously reduced, shall have virtually ceased, one may say that the future of Blue 

 whaling will be limited to the lifetime of those whales now surviving. 



INCREASE OF IMMATURE WHALES IN THE CATCH 



Intimately bound up with the decline in average length of the female catch is the rise 

 in the percentage of immature whales in the catch. For this we rely again on the figures 

 given in Hvalrddets Skrifter (No. 12, p. 20). The results have been expressed there for 

 the last five seasons in terms of the total Blue catch, that is to say the immature females 

 are shown as a function of the total catch, male and female. 



It is, I think, better to take the immature component of each sex as a function of the 

 total animals of that sex. I have, therefore, taken the immature females as percentages 

 of the female catch in each year, and the results are shown in the following table : 



