SEX RATIO 



267 



Table 21. Foetal sex ratio 



(From International Statistics and Discovery Committee's records) 



Table 21 shows the ratios of the sexes of foetuses recorded in the International 

 Statistics, and the sexes recorded by the Discovery Committee's staff are added. The 

 latter figures are really too small to be of much assistance. From this table it is clear that 

 there is no great difference in the numbers of each sex at birth. It seems almost certain, 

 however, that in Humpbacks rather more males than females are born, and highly 

 probable that in Blue and Fin whales also there are slightly more males. The figures for 

 Sei whales are inconclusive. 



Table 22 gives the numbers of each sex in different localities so far as they are re- 

 corded in the International Statistics, and here also the Discovery Committee's records 

 are added. It will be seen that in the totals for all localities males predominate over 

 females in Blue, Fin and Humpback whales. This might be caused by the absence of 

 many of the lactating females from the main whaling grounds (see p. 223), but, on the 

 other hand, we should expect some selection of females by the whalers on account of 

 their larger size. The balance of probability is that there are in fact slightly more males, 

 and this is supported by the foetal ratio. Records of the sexes of Sei whales are very 

 scarce in the International Statistics. There appear to be more females in the catches, 

 but the Sei is a small whale and hardly worth catching below a certain length. Conse- 

 quently the selection of females is greater than in other species (for, as in other species, 

 the female grows to a greater size than the male). Matthews (1938c, p. 187) shows that 

 up to a length of 15 m. males are commoner than females, and concludes that there is 

 actually an excess of males from early stages of foetal life. 



It is probable then that in all four species there are slightly more males than females. 



The sex ratio at different localities need not be discussed at much length, but certain 

 important facts are shown by Table 22. In the Antarctic pelagic catches Blue and Fin 

 whales always show an excess of males which usually form about 53-55 % of the total. 

 At South Georgia also male Fin whales are slightly in excess of females, but it is curious 

 that among Blue whales here the females appear always to predominate. Similarly, 

 there is an excess of male Fin and female Blue whales in the winter catches at temperate 



