THE AGES OF WHALES 



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These observations, being made on the dorsal and lumbar vertebrae near the middle 

 of the vertebral column, should, if Flower is correct, be sufficient in most cases to show 

 whether or not fusion has spread through the whole column. 



Complete maturity appears to have been attained in three of the Blue males but in 

 none of the Blue females, although the largest measured over 26 m. Only one vertebra 

 was examined in No. 1109, so that one cannot be certain about the whole column, but 

 there is little doubt that Nos. iioo and 1029 were fully mature. From this it appears 

 that male Blue whales reach full physical maturity at somewhere about 25 m. and females 

 at some length over 26 m., but the data are of course extremely meagre. The data 

 for Fin whales suggest about 21 m. as the corresponding length in males and probably 

 22 or more metres in females. 



As was to be expected these observations give further evidence that females are 

 normally of greater size than males. 



It has been pointed out in the section on the reproductive organs that a clue to the 

 age of a female whale is to be found in the remains of the corpora lutea of the ovaries. 

 At the end of its existence as a functional body (i.e. very soon after parturition; or, if 

 the ovum is not fertilized, after presumably a much shorter period) the corpus luteum 

 shrinks to a small fibrous body. Old corpora lutea formed in this way may accumulate, 

 owing to their longevity, in considerable numbers in whales which have been adult 

 sufficiently long. Thus a whale with a large number of corpora lutea is almost certainly 

 older than one with a small number, and if one large group of females on the average 

 has more corpora lutea than another group, there is hardly any doubt that they are on 

 the average older whales. We may make use of this in a general comparison of the 

 ages of the whales caught in successive seasons and examined by us. The figures are 

 as follows : 



Blue Whales 



* In which the total number of functional and old corpora lutea could be counted. 



It is seen from this that female Blue whales averaged about the same age during the 

 second part of the 1924-5 season at South Georgia and during the 1925-6 season at 

 South Georgia and the 1926 season at Saldanha Bay. But it is evident that their ages 

 were, in general, distinctly greater in the 1926-7 season at South Georgia. 



In the case of Fin whales (see table overleaf) it appears that in all four seasons 

 there was no marked difference in the average ages. 



It has been shown that the difficulty of estimating a whale's actual age from the 

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