THE FUTURE OF WHALES AND WHALING 



413 



Figure 22g. Lower jaw of a Sperm Whale with an old fracture pseudarthrosed at an angle 

 of go . Aboard the Willem Barendsz, ig^i-ig^s season. [Photograph: N. J. Teljer.) 



to Brown and Norris's investigations of White-beaked Dolphins, abscesses 

 are quite common in such, and similar, cases. 



While there is nothing strange about whales and dolphins fighting 

 among themselves, what is strange is that the resulting serious injuries and 

 fractures heal up again. Clearly even the weak and injured among them 

 can, because of the extremely favourable circumstances in which they 

 live, recover and survive. 



From analogies with other mammals, we may take it that the death 

 rate in the years immediately following the first is of the order of 2-5 per 

 cent of the total age group in question. Naturally, this percentage increases 

 with old age since whales, after all, are not immortal, and, like most 

 animals, few of them live to the maximum age. Unfortunately, we do not 

 yet know precisely at what age the death rate rises perceptibly. 



However, there is one method by which the natural death rate of 

 individual age groups can be assessed, viz. by investigating the age dis- 

 tribution of a given population. By investigating, say, 1,000 animals of 

 the annual catch, and by establishing how many of them are below the 

 ages of I, 2, 3, 4, etc., we can calculate the average death rate (from 

 natural and man-made causes) for every age level, provided only that, 

 first, the ages are very accurately determined (and as we have seen this is 

 not yet possible in Cetaceans though it seems possible that we may have 

 more certainty in the fairly near future), and that, secondly, we know 

 whether the population is static, increasing, or decreasing. Now, on the 

 second point we have even less certainty than on the first, since to establish 

 it is after all the whole purpose of the investigation. Moreover, we must 



