354 



DISCOVERY REPORTS 



paper (Wheeler, 1930), in which it is shown that physical maturity is correlated with the 

 presence of fifteen corpora lutea in the ovaries and reasons are given for considering 

 that females with from one to four corpora lutea are in their first or second year from 

 sexual maturity; those with from five to nine corpora lutea are in their third or fourth 

 year from sexual maturity ; those with from ten to fourteen are in their fifth or sixth 

 year, and so on. 



Such a method of estimation is, of course, applicable only to females. No way is yet 

 known by which the age of the mature male whale can be determined. Also, as Blue 

 whales have not figured in the catches to the same extent as Fins, our conclusions are 

 confined to the latter species. 



Observations made by the Discovery staff cover seven seasons during five of which 

 almost the entire catch of the company was examined. Some months of fishing were 

 unavoidably missed in each of the remaining seasons, and, as will be shown later, this 

 is a matter of importance when assessing the representative nature of the catch. 



The total number of female Fin whales recorded was 879, but of these 277 were 

 shown to be sexually immature by examination of the internal genitalia, and 130 were 

 so badly decomposed, or so badly damaged internally, that the genitalia could not be 

 examined. An approximate division of this last group into sexually mature and immature 

 can, of course, be made using length as criterion (Mackintosh and Wheeler, p. 417), 

 and the figures then read 281 immature (32 per cent of the total) and 598 mature whales. 

 In 472 of the latter full ovarian records are available. 



The analysis of the 472 sexually mature whales into two-year groups commencing at 

 sexual maturity and dependent upon the number of corpora lutea is as follows : 



Table I 

 Female Fin whales 



The taking of an annual unselected sample from an ageing stock to which annual 

 additions are made at the lower age limit (which is, in effect, what the whaling com- 

 panies have been doing) results inevitably in a heightening of the progressive diminution 

 among the older members of the catch naturally caused by ordinary mortality. The 



