BREEDING AND GROWTH 419 



The most striking result shown by this table is the generally high percentage of 

 immature whales. The figures for males and females correspond fairly closely in both 

 species, but the percentage of immature Blue whales is usually higher than in the case 

 of Fin whales. 



At South Georgia, perhaps the most important fact is that there is always a higher 

 percentage of immature whales in the second half of the season than in the first. In- 

 cluded above are three second-half seasons and two first-half seasons. Among Blue 

 whales the percentage of immature whales in the first half of the season is about 

 20 per cent or 30 per cent, but in the second half of the season usually more than half, 

 and in one case 78 per cent, of the whales are immature. 



The same phenomenon is to be seen in the case of Fin whales. Here the immature 

 whales are mostly under 10 per cent of the total in the earlier part of the season, but 

 rise to 30 per cent or 40 per cent in the second half of the season. 



These figures are, of course, a reflection of certain features of the migrations and move- 

 ments of the whales, and it appears that there is a general tendency for the large whales 

 to visit the coasts of South Georgia first, and for the smaller whales to come on later. 

 The significance of this will be discussed in a later section. 



One other feature may be pointed out in the figures for South Georgia and that is 

 that there is a definitely lower percentage of immature Blue whales in the 1926-7 

 season than in the two preceding seasons. This is due to the exceptional nature of the 

 catches of Blue whales, which were present in very large numbers throughout most of 

 the season, and which were of a large average size. This again is dealt with more fully 

 later on. 



Of the figures for Saldanha Bay there is little to be said beyond the fact that almost 

 the entire catch (from 80 per cent to 90 per cent) consists of immature whales. The catches 

 at Saldanha Bay are fairly uniform throughout the season and there seems little to be 

 gained by a comparison here between the first and second halves of the season. 



The proportion of immature whales in the catches needs careful scrutiny from the 

 economic point of view. As has been pointed out on various occasions, the killing of 

 immature whales is economically undesirable, as it means that these whales have no 

 chance of reproducing. To express in a difi"erent way what is perhaps the same thing, 

 one may say that a high percentage of immature whales in the catches is a reflection of 

 a general decrease in the average length of the whales. Now it is known that one of the 

 first eff"ects of the depletion of a community of animals is a general decrease in size, 

 which results from the likelihood that an individual is killed before it has time to grow 

 to its full size. Thus, where an unnaturally high percentage of immature whales is 

 found, excessive hunting may be suspected. At Saldanha Bay, however, the high 

 proportion of immature whales is not due to this cause but to the segregation of young 

 whales in that particular region. The whole question will be examined, however, when 

 the movements and distribution of the whales come to be considered. 



