370 DISCOVERY REPORTS 



We examined 570 Fins of which 272 were female, and 70 of these females were 

 sexually immature. From the mature females 189 ovarian records were obtained. The 

 remaining 13 were decomposed to such an extent that the number of corpora lutea could 

 not be determined with certainty. They were sexually mature, however, and we have 

 to consider the immatures in relation to our full sample of 272 ; while the age series 

 determined by the corpora lutea represents the distribution of age groups among 189 

 sexually mature whales. In Table V the percentages have been calculated as though 

 the entire sample had been examined. 



The percentage of immatures in our sample of the population is 257. Among them 

 are five of small size (see Table IV), three of which had evidently not long been weaned. 

 They were less than one year old. The other two had two series of scars, suggesting 

 from this together with their size that they were very late calves of the previous season 

 and were thus in their second year when killed. From the two series of scars marking 

 33 immatures, with one whale of 167 m. with one scar series, and the two small ones 

 already noted, we have 36 whales more than one but less than two years old. Whales of 

 nearly three years include 26 immatures as well as ten mature whales with two series of 

 scars and 53 with three. The mature whales are, however, included in the estimations 

 determined by the corpora lutea and we have already seen that 40 are nearly three or 

 nearly four years old and twelve are nearly four or five. The apparent disporportion of 

 immatures is now explained by the three successive year groups that are represented in 

 the catch. The earliest of these can for practical purposes be neglected, for not only is 

 the appearance of its representatives in the catch subject to penalty and only due to 

 accident, but it is almost certain that the figure obtained conveys a wrong impression of 

 the population. It is probable that large numbers of the newly weaned whales never 

 make the migration and this explanation covers the shortage of lactating and resting 

 whales of all ages which is a feature of the South Georgia catch. The large catches of 

 immature whales made at Saldanha Bay, South Africa, suggest that many of the early 

 calves are weaned and left in the coastal waters of the breeding areas, while late calves 

 are weaned during migration or even after arrival in southern waters. In support of this 

 I can point out that, although lactating whales are few, they are certainly more numerous 

 in the catches at the end of the South Georgia season than at the beginning. This must 

 not be taken to imply necessarily the identification of the South African whales with 

 those of South Georgia. It is supposed, however, that similar conditions prevail 

 wherever the breeding area may be. 



The original group of "immatures verging on maturity", i.e. the immatures more 

 than one but less than two years old, now form but 13 per cent of the sample catch. 

 On returning to the north, many of this group will commence to breed and they will 

 be accompanied on the next southern migration by the rest of the group (9I per cent 

 of the sample catch) which will not become mature until their return to northern waters 

 in the following winter when they are just three years old. 



With the aid of the estimations of age from Table II we can now sketch the relative 

 age composition of our sample as follows : 



