458 DISCOVERY REPORTS 



probability the majority of these whales normally become pregnant in alternate years, 

 practically never in successive years, but sometimes once in three years. The low per- 

 centage of lactating whales (i6 per cent in Blue whales and lo per cent in Fin whales) 

 is not sufficiently accounted for by the fact that the nursing period (about eight months) 

 is shorter than the period of gestation (ten to eleven months) and one must suppose 

 that the mother spends much of her time with the calf away from the areas of concen- 

 tration where the hunting is mostly carried on. 



The totals for South Georgia and South Africa provide now a more precise basis 

 for comparing the two localities. Taking first the ratio of immature whales we see that 

 whereas at South Georgia well over 50 per cent of the whales are adult the percentage 

 of immature whales at South Africa works out at about 80 per cent for Blue males and 

 females and Fin males and over 90 per cent in the case of Fin females. In the sub- 

 classes of female whales the most striking difference between the two localities appears 

 in the number of whales which had recently ovulated. Among the South Georgia 

 whales 4 per cent of the adult female Blue whales showed indications of having recently 

 ovulated and i per cent of the adult female Fin whales, while at South Africa 16 per 

 cent of the Blue and 50 per cent of the Fin females were in this condition. There is a 

 slightly higher percentage of pregnant whales at South Georgia than at Saldanha Bay. 

 This is to be expected since the period of gestation is mostly spent in the southward 

 migration. The figures for lactating whales are inconclusive. 



It will of course be realized that some of the distinctions between the whales of the 

 two localities are due to actual diff^erences in distribution, such as appear in, for instance, 

 the ratio of immature whales or the tendency towards fluctuation in the whale popula- 

 tion, and some are due simply to the fact that different months are being compared 

 (e.g. the different ratios of females ovulating or pregnant). 



The proportion of pregnant females at Saldanha Bay naturally shows a tendency to 

 increase as the season advances (i.e. as the pairing season advances) and the percentage 

 of immature Fin whales decreases fairly steadily. Apart from this, however, there 

 seems to be little fluctuation in the local whale population. 



The observed changes in the composition of the catches at South Georgia, however, 

 are of great importance. Reference should be made here both to the foregoing tables 

 and to Plates XLIII and XLIV which give a "bird's-eye" view of the catches in 

 respect of the numbers, sexes and sizes of all the Blue and Fin whales examined. In 

 the second half of the 1924-5 season (February-May 1925) Blue and Fin whales were 

 caught in roughly equal numbers and there was little fluctuation during these months 

 in respect of sex or size or of the proportions of pregnant, resting, lactating whales, etc. 

 The percentage of mature whales does not show any significant change except in the 

 case of Blue males, where it increases from very low figures in February and March to 

 relatively high ones in April and May. There was not much variation in the numbers 

 of whales caught, except that during the greater part of March comparatively few were 

 brought in. Small fluctuations like this, however, are not of great significance and are 

 often caused by bad weather or difficulty in locating the whales. Attention should be 



