404 WHALES 



spaced rings than those of Fin Whales, whose migratory habits (and whale- 

 bone rings) are far less regular. Thus, while the interval between maximum 

 feeding and maximum sexual activity is six months in Blue Whales, it is 

 four and eight months respectively in Fin Whales. 



The greatest number of rings found in any one Blue Whale is fifty-two, 

 and if we take it that the rings are bi-annual, Blue Whales have a life 

 expectancy of at least t^venty-six years. In a recent publication (1957), 

 Nishiwaki reports that he covmted eighty-six rings in the wax plugs of a 

 Fin Whale, -which may mean that Fin Whales live up to forty-three years, 

 a figure that agrees with Purves's conclusions. From Purves's and Nishi- 

 waki's reports, it appears that the average age of the animals is higher 

 than the average age found by Ruud with the baleen method. Now, the 

 wax plug method has the enormous advantage that it can rely on the fact 

 that the plugs are not worn down by friction, so that all the rings laid 

 down from birth can be counted^, while the whalebone method is, accord- 

 ing to Prof. Ruud himself, unreliable for periods longer than five years, 

 and quite useless for estimating the age of old whales. 



By means of the ear-plug method, it is therefore possible to tell when 

 whales reach sexual and physical maturity. Human beings stop growing 

 betAveen the ages of twenty-two and twenty-four, after which the last 

 epiphyses - the thin bony plates on the anterior and posterior faces of each 

 vertebra - fuse solidly with the middle mass of the centrum (the diaphyses) . 

 Now, since growth can only take place while some cartilage divides the 

 epiphyses from the diaphysis, their fusion is equivalent to physical 

 maturity. In all animals, fusion begins in the cervical and caudal regions, 

 the anterior thoracic vertebrae being the last to grow together. Thus, by 

 examining its vertebral column, we can tell what degree of physical 

 maturity a given whale has reached, and on this basis biologists believe 

 that Fin Whales are physically mature at about fifteen years (see the 

 table on p. 384), but this figure is subject to revision until, conclusive 

 evidence is presented. 



For, while biologists can use three methods of estimating the age of 

 whales (corpora albicantia, baleen periods, and ear-plug bands), and 

 while there is some measure of agreement between the results obtained by 

 the several methods, it must be stressed that none of them is conclusive. 

 To be conclusive, any method would have to be tested on an animal whose 

 real age was known beforehand, and this involves marking very young 

 animals whose real age at marking can then be estimated within a few 

 months. However, this method has met with resistance from gunners who 

 claim that early marking may have fatal effects on young whales. 



Dawbin, however, who marked a large number of Humpback calves 



^ However, it is very difficult to make reliable counts of early rings. 



