THE STOCK OF WHALES AT SOUTH GEORGIA 361 



All these figures are based on the catch for five seasons and it is necessary to find out 

 how many whales can be produced by the remaining stock in two years, since each 

 female gives birth normally to one whale in this period. This number is readily obtained 

 by taking two-fifths of the mature whales which survive catching and are not absent 

 from the catching area for other reasons, i.e. two-fifths of column 5 minus column 6. 

 The numbers for each age class are given in column 7 and the sum — 464 — represents 

 the number of whales of both sexes that can, in the most favourable circumstances, be 

 produced by the mature stock. Roughly 232 of these will be females. 



Now the theoretical stock of immature females for five seasons has already been 

 worked out and two-fifths of this number (269) gives the initial immature stock for two 

 years. It follows, therefore, since 269 immature females are necessary to keep the stock 

 at its present level and only 232 females can be produced, that considerable damage is 

 being done. 



If, however, the older whales that are absent from the South Georgia population are 

 not eliminated, but are still adding to the immature stock and are subject elsewhere to 

 the same rate of reduction, the total of surviving mature females will be considerably 

 greater. In column 8 the numbers of surviving stock of the different age classes are 

 given supposing that no whales are missing; and the number of immature females 

 produced — 269, half the sum of this column — will just balance the losses and the stock 

 will remain stable. It should be remembered that the figures for the reproduction of the 

 stock are optimum values and that probably the conditions necessary to attain them 

 are never reached. 



While again stressing the indicative rather than the exact nature of the results it 

 appears probable that on these lines some definition can be given to the effect of the 

 fishery upon the whale population in this area. 



A more difficult question is that of the killing of immature whales. The number of 

 immatures in the South Georgia catches has been lately remarked on by Hjort, Lie and 

 Ruud (1932) — "Why is it that in certain areas, especially where whaling has gone on 

 for 25 years (from the old land stations) there are larger numbers of young animals than 

 elsewhere? We cannot infer that more young animals are caught on the old grounds 

 because the stock has decreased ... it appears more likely that the young animals have a 

 migration route or area of distribution of their own, which does not quite coincide with 

 that of the adult whales". 



The sexually immature females formed 32 per cent of the total catch examined by 

 us, which is, on the face of it, an alarming proportion, if, as we have supposed, all the 

 immatures are between the ages of one and two years. Up to the present we have had 

 no method of age determination among the immatures except that afforded by deduction 

 from length frequency. By utilizing such evidence as was available in 1928 the life 

 history up to the time of sexual maturity was suggested by us as follows (Mackintosh 

 and Wheeler, 1929, p. 444). Birth takes place at about 6-5 metres. Weaning at about 

 12 metres some six or seven months after birth in early summer when presumably 

 mother and calf have migrated southward during the spring. On the analogy of the 



