BREEDING AND GROWTH 433 



It is a pity that no Fin whales of less than 12-0 m. were seen, but it may be gathered 

 that weaning in this species takes place when the calf is in fact about 12-0 m. long. 

 There are not quite adequate data for the construction of the curve of baleen growth 

 (see p. 355) and the first half of it rather depends on analogy with the curve for Blue 

 whales, but it is evident from the plotted points that no spurt in growth takes place 

 after the calf has reached much more than 13-0 m. and one may expect that it occurs 

 between 12-0 m. and 13-0 m. All the whales over 12-0 m. were weaned except perhaps 

 one. This one (No. 84 mentioned above) was probably unweaned, and it merely serves 

 to show that if a Fin whale can reach 13-55 "^- before being weaned, the normal length 

 at which Fin whales are weaned is not likely to be far below i2-o m. It might in fact 

 be above 12-0 m., for No. 891 (12-3 m.) might have been weaned earlier than usual. 

 Hinton refers to two records of Fin whale calves of 40 ft. and 45 ft. (i.e. 12-2 m. and 

 13-7 m.) from the North Atlantic which were suspected of being fed on milk owing 

 to a yellowish substance found in the stomach. 



In any case, until further material has been collected, it may be assumed that Blue 

 whales are weaned on the average at i6-o m. and Fin whales at 12-0 m. The difference 

 between these two lengths is very striking, especially as it actually exceeds the difference 

 between the lengths at which the two species become sexually mature, but it seems 

 impossible to avoid the conclusion that if the growth of the baleen of Fin whales re- 

 sembles that of Blue whales, the increase in the rate of growth takes place when the 

 Fin whale is 4-0 m. shorter than the Blue whale. 



In an estimation of the rate of growth of the calf during lactation and the length of 

 the nursing period, an examination of the ratio of mature females which are nursing 

 is not of much assistance, for their appearance is very irregular and there is a probability 

 that a part of the nursing period is spent in some seclusion or segregation from the main 

 herds, so that the proportion represented by those which do appear on the whaling 

 grounds is uncertain. Furthermore, it must be remembered that the killing of females 

 accompanied by a calf is prohibited in the Dependencies. From the accounts of the 

 whalers it seems that young calves are very rarely seen in the Dependencies but 

 are commoner off the South African coasts. This is to be expected since the calves 

 appear to be born early in the southern winter when the mothers have travelled 

 north into the warmer waters. Small calves are of course seldom killed by the South 

 African whalers as they are scarcely worth pursuing, but, as is pointed out in the section 

 on blubber, the lactating whales examined at Saldanha Bay were very fat compared 

 with those at South Georgia, indicating a comparatively early stage in the nursing period. 

 It happens occasionally at South African stations that sucking calves are killed and when 

 this occurs valuable evidence is provided as to the rate of growth during the nursing 

 period. At South Georgia Blue whales of less than i6-o m. or Fin whales of less than 

 13-0 m. are practically never captured. 



As scarcely any small calves have appeared in the course of our work it is necessary 

 to turn elsewhere to find material on which to extend the curve of growth. Records 

 of calves are extremely scarce, but among the statistics furnished to the British Museum 



K IV ^3 



