MULTIPAROUS FEMALES 447 



rarely seen in the Dependencies, though relatively common off the South African coasts (p. 433). 

 They also believe that in some cases ' the calf is weaned on the small and rather scarce krill ' in South 

 African waters 'and remains in the northerly regions for the first summer' (p. 437). 



It is not at all improbable that fin whale calves should be weaned in regions which are not very rich 

 in plankton. Thus, we can be certain that humpback whale calves are almost invariably weaned at the 

 end of a northward migration, in waters relatively poor in plankton (Chittleborough, 1958). The minke 

 whale provides a better parallel with the fin whale. Lactating female minke whales are not found 

 in the Arctic, although they are found in Lofoten waters in small numbers, and Jonsgard (195 1) 

 suggested that most are weaned before they immigrate to Norwegian waters from lower latitudes. 



It is suggested that in the fin whale the calf is weaned on average in December, and that in the 

 majority of cases weaning occurs north of the antarctic whaling grounds, if not north of the Antarctic 



60 



N 



M 



D J F 



MONTHS 



Text-fig. 50. Monthly percentage frequency ( + 2 S.E.) of lactating females in the South Georgia catches (A), 



and the pelagic catches (B) of mature females. 



Convergence. It is clear that (even if we allow that lactating females are under-represented in the 

 catches owing to the prohibition on their capture), lactating females are not present on the whaling 

 grounds in representative numbers in the early part of the season. This hypothesis explains why no 

 very early post-ovulation stages in the development of the corpus luteum have been recovered in the 

 Antarctic (p. 443), because if weaning and the post-lactation ovulation usually occur to the north of 

 the whaling grounds, then the very early post-ovulation stages might well be unrepresented or very 

 under-represented on the whaling grounds. 



Some lactating females are, however, taken on the whaling grounds, although the evidence pre- 

 sented above suggests that in a large proportion of these the secretion of milk has actually ceased. 

 It may well be that some of the others have also weaned their calves very recently, but that the process 

 of milk secretion has not yet ceased. In this connexion it may be thought to be significant that, in 

 explaining infractions of paragraph 3 of the Schedule to the International Whaling Convention, 1946 

 (which prohibits the taking of calves or females accompanied by calves), the gunners almost invariably 

 state that no calf was seen. They are heavily penalized for taking lactating whales, but their denials 

 have some support from the evidence given here. 



A further point, which should now be discussed, concerns the difference in the incidence of lactating 



16 



