THE FUTURE OF WHALES AND WHALING 399 



population, which may be supposed to have been anything from 250,000 

 to 500,000. 



So much for the total population, but what of annual increases ? To 

 calculate these, we must know at what age the animals reach puberty, 

 how much later a given cow has her first calf, what the normal life 

 expectancy of the cow is, how many calves she can have throughout the 

 rest of her life, and finally what the ratio of bulls to cows is. To start with 

 the last point, whaling statistics which indicate, inter alia, the sex of foetuses, 

 indicate that the same number of Rorqual and Sperm Whale bulls and 

 cows are born annually, and that this ratio is subsequently maintained. 



In Chapter 13 we saw that, by examining their reproductive organs, 

 we can tell whether whales have reached sexual maturity or not, and that 

 whaling statistics and other data enable us to estimate the interval between 

 successive births. In basing our calculations on these data, however, we 

 must clearly bear in mind that, for instance, the figures on p. 384 are only 

 reliable if our estimates of the age of the animals are correct. Now, while 

 we cannot tell the precise age of a given whale, we have a rough method 

 of estimating it, and since all our conclusions depend on the accuracy of 

 this method, we shall now look at it more closely. 



While length can tell us something about the age of very young animals, 

 it is no indication of the age of mature ones, since an old whale, like an old 

 man, may be shorter than a much younger one. We shall say little about 

 Mackintosh and Wheeler's method (1929), since their age determinations 

 by means of examining the degree of healing of external scars applies to 

 maximum periods of three years, and can, moreover, give rise to grave 

 misinterpretations. Another method suggested by Mackintosh and Wheeler 

 which was subsequently used by many other biologists (Wheeler, 1930; 

 Laurie, 1937; Peters, 1939; Zemski, 1940) is far more promising. This 

 method is based on counts of corpora albicantia in the ovaries (see Figs. 

 199 and 200). In Chapter 13 we saw that these corpora are indications of 

 ovulations and that, in whales, they never disappear. Now, counts of the 

 corpora albicantia of captured Fin Whale cows have shown a distinct 

 periodicity from which it appears that 2 -8 white bodies are formed every 

 two years (Laws; p. 389), and that the age of a cow can therefore be 

 estimated fairly accurately from the number of corpora albicantia in a 

 given ovary, provided that the age at sexual maturity is known. 



In 1948, Nishiwaki and Hayashi, two Japanese biologists, discovered 

 that in whales, as in many other animals, man included, the colour of the 

 lens of the eye changes with increasing age. The lens is colourless in 

 young animals and gradually turns a golden colour. (The absorption of 

 light can be measured with a photometer.) However, since no particular 

 tint could be associated with a given age, and since, moreover, there was 



