CONDITION OF THE STOCK UNDER WHALING 289 



United States and recognized by a marked harpoon as one earlier struck upon the coast of Peru 

 (1852, p. 239). 



Concerning northern and southern sperm whales, the possibility among males of a size difference 

 at sexual maturity has prompted me to compare from seven oceans the smoothed length frequencies 

 of 54,456 males and 3475 females, which are all the relevant data available to me and comprise records 

 in the International Whaling Statistics, the records from Fayal, and unpublished figures in the British 

 Museum records. The curves which were constructed tend to suggest that both males and females 

 may grow a foot or two longer in the southern hemisphere, but they are not conclusive and I have 

 therefore refrained from publishing them here. What is required is a comparative study of the mean 

 lengths at which physical maturity is achieved in the different oceans. 



Should any difference in growth and size be eventually established between northern and southern 

 sperm whales, then the difference would either be due to environment or to racial segregation. Since 

 the parasitic diatom Navicula sp. appears to be bipolar, it is likely that the northern and southern 

 stocks mingle to some extent in equatorial and tropical latitudes where the whales presumably carry 

 sufficient residual diatom population to effect contagion even though a diatom film is not visible. If 

 such mingling occurs, and if there were any racial difference between the stocks, then the female 

 sexual seasons at opposed times might be supposed to function as a mechanism preserving the racial 

 ' difference. But this is unlikely because the difference in time of the female sexual seasons is presum- 

 ably a physiological adaptation to the environment, and any whales which move from one hemisphere 

 to another would no doubt change their breeding rhythm accordingly, just as do certain ruminants 

 when introduced into the opposed hemisphere (Olstad, 1930; Marshall, 1937). I am inclined to 

 think that if any difference in size does exist between northern and southern sperm whales, then 

 its origin is environmental rather than genetic. Possibly the food supply is greater in the southern 

 hemisphere. 



Turning to the Azores stock, there is no reason to believe that this is isolated in any way. Apart 

 from Wilkes' remark (p. 282) that whaling was not conducted beyond some 200 miles from the 

 islands, there is no evidence that the summer whales are confined to the neighbourhood of the 

 Azores, but any segregation which may occur is presumably not maintained to the southward where 

 in spring pairing takes place among the migrant part and where we may suppose there is latitudinal 

 continuity, and consequent genetic interchange, with other Atlantic sperm whales. 



CONDITION OF THE STOCK UNDER WHALING 



My account of the Azores whale fishery (Clarke, 1954a) describes how open boat whaling, after a 

 long period of depression or indifferent prosperity, was intensified in the years which followed the 

 outbreak of the Second World War. The numbers of whaleboats and motor tow-boats were increased 

 and the catching power improved by the introduction of radio-telephone communication between 

 cliff look-outs and the motor boats. In such times of expanding industry it seems desirable, as 

 Figueiredo has earlier pointed out (1946, p. 216), that the effect of whaling and the requirements of 

 conservation should be kept under review as much in the Azores as in modern steam whaling centres 

 elsewhere. 



The effect of zvhaling 

 Since the major part of the Azores stock of whales, including all or virtually all the females, is believed 

 to migrate to the southward or southeastward in winter (p. 285), the survival of the stock is likely to 

 be favoured by the fact that no whaling is nowadays conducted around the Cape Verde Islands or the 



