466 



DISCOVERY REPORTS 



The apparent constitution of the stock, i.e. the ratios of the different classes of Blue 

 and Fin whales examined at South Georgia, is as follows : 



In contrast to the population in the S.W. African region, that at South Georgia 

 seems to have a generalized character which suggests that it may not be very far from 

 representing the stock as a whole. One point, however, in which it might be found 

 to differ substantially from the real constitution of the stock is in the ratio of im- 

 mature whales. It is difficult to believe that any community of mammals normally 

 includes 30 per cent or 40 per cent of immature individuals. In the case of whales, 

 among which the immature appear not to exceed two years of age, it would mean that 

 the "expectation of life" for a whale was extraordinarily short. It must not be for- 

 gotten, however, that the effect of hunting is to shorten the expectation of life, and 

 that such evidence which exists as to the ages of whales does suggest that the majority 

 are unexpectedly young. 



There is not sufficient data on which to base an actual estimation of the real con- 

 stitution of the stock of southern Blue and Fin whales, but it may be hoped that future 

 investigations will provide sufficient information for this purpose. It will then be possible 

 to estimate the birth rate and hence the fraction of the stock which might reasonably 

 be killed annually for commercial purposes. 



Future work may be profitably directed among other things to the question of the 

 numerical equilibrium of the whole community of whales, and any enquiry into the 

 effect of hunting must take into consideration the natural factors which limit the size 

 of the stock. Under natural conditions it is to be supposed that in the long run the 

 number of deaths equals the number of births. If these deaths are simply the result 

 of the number of whales exceeding the maximum for which there is, so to speak, room 

 (e.g. if the number is limited by, say, the amount of food available), then a number 

 equal to the number to be born each year may be killed annually. On the other hand, 

 if the deaths were due to causes operating independently of the size of the stock (e.g. 

 attacks by killer whales, deaths from old age, etc.), then any deaths from hunting will 

 add to, and not replace, the deaths from natural causes, and will therefore tend to cause 

 depletion. The equilibrium of the stock is probably influenced by both types of factor. 



It will obviously be of no practical value to calculate the percentage of the whole 

 stock which may safely be killed annually unless some kind of estimate can be made of 

 the total number of whales in the whole community. Anything approaching an accurate 



