THE STOCK OF WHALES 465 



sometimes extends to three years. The point to be emphasized here is that, since normally 

 only one whale is born at a time, an adult female can at the most produce only one young 

 every two years. The rate of reproduction is thus very slow. 



7. The hypothesis that gestation in these whales occupies nearly a year is confirmed 

 and it has been shown by evidence from more than one source that the young whale 

 grows up to sexual maturity in about two years after birth, during rather less than half 

 of which period it is nourished by the mother. Thus the slowness of the rate of pro- 

 pagation is to some extent counterbalanced by the rate at which the young grow to 

 sexual maturity. The most important point is perhaps that the immature whales which 

 can least be spared to the stock are exposed to danger for a comparatively short period. 

 In view of this it is curious that so high a proportion of immature whales appears 

 among the catches. The phenomenon may be largely due to differences in the distribu- 

 tion of the adult and immature whales. 



8. Owing to segregation in a greater or lesser degree, different areas may harbour 

 communities of whales which are differently constituted in respect of age, proportions 

 of different classes, etc. Different whaling centres must thus be examined individually 

 when any measures for the control of the industry are considered. Further, in an 

 area such as that of South Georgia, where the whale population undergoes funda- 

 mental changes in the course of the season, the effect on the stock as a whole of 

 hunting at different times of year needs to be taken into account. So far as the 

 three seasons, over which the observations have extended, are concerned, it is not 

 easy to say whether the killing of whales in the earlier or later part of the season has 

 had the greater effect. On the one hand a higher percentage of pregnant females is 

 killed in the earlier part of the season and the majority of whales are less "fat" than 

 later on, while on the other hand many more immature whales are killed in the second 

 half of the season. At South Africa the whale population shows little or no sign of 

 changing during the season, and it may be supposed that whereas at South Georgia 

 a large number of whales are exposed to danger for a short time, at South Africa a 

 smaller number are exposed to danger for a longer time. 



In connection with the effect of hunting on the stock of whales it is desirable that as 

 much as possible should be known of the composition both of local communities and 

 of the stock as a whole, in respect of the relative numbers of the two sexes and of whales 

 in different stages of the reproductive cycle at any given time. 



The analysis of the whales examined during the work, which is shown in the tables 

 on pp. 456 and 457, may be taken as representative of the catches as a whole at South 

 Georgia during the period over which the observations extended. But the catches at 

 South Georgia, as already explained, are not necessarily representative of the whole 

 stock of southern Blue and Fin whales, and a distinction must therefore be drawn 

 between what might be called the apparent and the real constitution of the stock as a 

 whole. 



KIV 27 



