THE FUTURE OF WHALES AND WHALING 407 



With the help of what data we have on the time of puberty, on the 

 maximum hfe expectancy, and on the frequency of successive births (see 

 p. 389), we can therefore arrive at the tentative figures of a cow's normal 

 number of offspring shown in our table, which are based on the assump- 

 tion that the cow is allowed to live out her span. 



We have now come to the end of our discussion of the yearly increase 

 of the Rorqual population, and we have still to investigate their annual 

 decrease through natural causes. In fact, the problems here are greater 

 still, for if we can occasionally witness the birth of a Cetacean, its death 

 always occurs in the hidden depths of the ocean, so that we have no 

 observations whatsoever on this point. Hence all our knowledge is based 

 on inferences from other mammals, and since this knowledge, too, is very 

 scanty and since, moreover, some of these mammals, e.g. various rodents, 

 are not at all comparable to Cetaceans, what we know with any degree 

 of certainty is very little indeed. 



All things being equal, we may assume that Cetaceans have a higher 

 mortality rate during the first year of life than during subsequent years, 

 just like all the terrestrial animals investigated so far, such large species 

 as the European bison included. Now this assumption seems reasonable 

 if we consider that Cetaceans, like other mammals, suffer from birth 

 traumata and the after-effects of weaning, and that they are at their most 

 helpless during the first year, when they fall victim to infantile diseases, 

 parasites and enemies. Gilmore (1958) reports the presence of a fairly 

 large number of still-born and young baby whale carcasses on the beaches 

 of Californian lagoons, but of only a very occasional adult carcass. The 

 infantile mortality rate during the first year of the life of terrestrial 

 mammals is estimated by various sources at from 15 to 50 per cent of the 

 total number of births in a given year, and as high as 40-50 per cent 

 in llamas, red deer and foxes. The figures for seals are also said to be of 

 that order; here the high infantile death rate is largely due to parasites 

 and Killer Whales, and from our discussion of these two factors in 

 Chapters 6 and 10, it seems reasonable to think that young Cetaceans fare 

 no better than young seals. Young dolphins have to add sharks to the list 

 of their natural enemies, while all Cetaceans are known to be subject to 

 serious parasitic infestation, particularly during the first month after 

 weaning. 



Their first birthday over, most animals may therefore be said to have 

 left the worst behind them. Naturally, they can still meet with fatal 

 accidents, and porpoises, for instance, often die in large numbers in the 

 Baltic \vhen the sea freezes over before they have migrated from it, while 

 Little Piked Whales are believed to perish from similar causes in the 

 Antarctic. Figs. 223 and 224 show photographs taken in 1957 by members 



