284 DISCOVERY REPORTS 



whales they concluded that the catch at this point would be one-seventh of the stock, 

 and with a suitable allowance for mortality could therefore work out the size of the stock 

 from year to year. The results obtained by this method when applied to the Iceland 

 fishery compared fairly well with the results obtained by Helland's method. 



These mathematical methods are described here only in the barest outline, and when 

 put into practice they are of course beset with difficulties. The primary assumptions on 

 which they are based are not more than approximately correct, and various allowances 

 must be made such as for irregularities in the rate of decline of the catches and changes 

 in the catching capacity of the industry arising from technical, economic and political 

 factors and weather conditions. There is the question whether the catches year by year 

 are representative of the same stock, and calculations of the rate of regeneration are 

 based on estimates of growth and rate of propagation, some of which at least require 

 confirmation (see pp. 221-5). Hjort, Jahn and Ottestad fully admitted these difficulties 

 and made it clear that their purpose was to expound possible methods of estimating the 

 magnitude of the stock, pending the accumulation of adequate statistics and fuller know- 

 ledge of the relevant biological factors. They considered, however, that such methods 

 could at least be used to estimate the minimum stock which must exist in the Antarctic 

 if current whaling activities were not to result in disastrous depletion. 



The position is that there are several methods by which it should in theory be possible 

 to calculate the approximate magnitude of the stock of whales. Individually they are 

 unreliable, since each involves certain doubtful assumptions or is affected by uncertain 

 factors. When our knowledge of the reproduction, growth, age and distribution of whales 

 has become more precise, and when statistics of catches cover an adequate series of 

 years, these calculations should become more reliable ; and if then approximately the 

 same estimates are obtained by different means they could be accepted with some con- 

 fidence. Further, if the estimates of the relative abundance of Blue, Fin and Humpback 

 whales given on p. 266 are accepted, an estimate of the stock of one species would pro- 

 vide also an approximate figure for the other two. We may at least hope to be able to 

 state maximum and minimum figures not too far apart to be of practical value. 



THE EFFECT ON THE STOCK OF WHALING AT DIFFERENT 

 TIMES AND IN DIFFERENT PLACES 



It is generally agreed that measures are necessary for the conservation of the stocks of 

 whales in the Southern Ocean, but since we are not yet in a position to calculate the 

 number of whales which could be taken and yet replaced by natural regeneration, the 

 measures so far adopted for the regulation of the industry have been framed with the 

 general purpose of checking the rate of depletion rather than of aiming at a strictly 

 rational annual catch. There are several possible methods of doing this. Protection can 

 be given to certain species and classes of whales, the whaling seasons can be limited, 

 geographical restrictions can be imposed (for example, by the institution of sanctuaries) 

 and the catching capacity of the industry can be regulated (e.g. by limiting production 

 or the numbers of factories and catchers). A full discussion on the regulation of whaling, 



