2 8 2 DISCOVERY REPORTS 



localities, and of course there has been a substantial reduction in the intensity of whaling 

 in war time. We have to keep in mind, however, the likelihood of the resumption of 

 intensive whaling after the war. It is sometimes argued that since whaling would cease 

 when the stocks were reduced below the economic level, they could never approach 

 extermination. It must be remembered, however, that so long as there are enough Fin 

 whales to keep the whaling fleet at sea the scarcer species might continue to be caught 

 from time to time until they were reduced almost to vanishing point. 



Further evidence that the Humpback and Blue whales are the species most in need 

 of protection is supplied by Rayner (1940, pp. 273-4), wno states tnat tne number of 

 marks recovered from each species expressed as a percentage of the number of that 

 species which have been marked, is 4-94 % in Blue, 3-01 % in Fin and 6-59 % in Hump- 

 backs. Although the number of marked whales killed must be higher than the number 

 of marks actually recovered, the percentage of marks returned must be more or less 

 comparable between the three species. The fact that the rate of recovery of marks from 

 Blue whales is higher than from Fin whales, and that the rate of recovery from Hump- 

 backs is higher than from Blues, can only mean that Blue whales have been losing a 

 bigger fraction of the stock on the whaling grounds than have Fin whales, and that 

 Humpbacks have been losing an even bigger fraction than Blue whales. Thus not only 

 is depletion more evident in Blue than in Fin whales, but the rate of depletion must have 

 been greater in Blue whales and greater still in Humpbacks. 



In view of the local heavy declines in the catches of Humpbacks, of the greater 

 vulnerability of this species and its high relative rate of loss, it can hardly be doubted that 

 this is the species most in need of protection, even though it is of less economic im- 

 portance than the other two, and this was recognized at the International Conference 

 referred to above. 



PROSPECTS OF ESTIMATING THE ABSOLUTE MAGNITUDE OF THE STOCK 

 No method has yet been found for making any reliable estimate of the absolute 

 magnitude of the stock of whales in the Southern Ocean, and although the problem 

 seems to present almost insuperable difficulties it is by no means hopeless. There are 

 several possible methods of gaining at least a clue, and although the data are at present 

 inadequate for any useful calculations to be made, the matter is of sufficient importance 

 for the prospects at least to be considered. 



In the first place there is the method of direct observation. If we know the approxi- 

 mate limits say of the zone inhabited by whales in summer in the southern part of the 

 Southern Ocean, and if all whales seen are counted from a ship making a sufficient 

 number of random cruises through this zone, the number of whales counted should bear 

 the same relation to the whole stock as the area of the belt of ocean viewed from the ship 

 bears to the whole zone populated by the whales. A considerable body of such data has 

 been accumulated by the Discovery Committee's ships, but an estimate on this basis 

 would be unreliable in itself, mainly because of the extreme difficulty of making due 

 allowance for changing conditions of visibility, and hence of calculating the area fairly 



