414 DISCOVERY REPORTS 



South Georgia are not very useful as there are only seven, but for the North Atlantic 

 the majority of pairings is estimated to fall in December, February and March, but they 

 are spread over a longer period and are much less conclusive than in the case of Fin whales. 



The next paper to be mentioned is that of Andrews (1916) on the Pacific Grey whale, 

 Rhachianectes glaiicus. It has been possible to make some direct observations on the 

 migrations and breeding of this whale, and these observations provide by analogy some 

 useful evidence on the breeding of the other whalebone whales. The period of gestation 

 in this species is clearly about one year, and it has been shown that subsequent growth 

 is remarkably rapid. 



It has already been mentioned that a detailed examination of some of the whalers' 

 statistics has been made by Harmer, special attention having been paid to an analysis of 

 the records of foetuses with a view to calculating the pairing dates and ascertaining the 

 limits of the breeding season and the months in which the breeding activities reach a 

 maximum. The more important results are incorporated in an account of the southern 

 whaling industry in the Report of the Interdepartmental Committee on Research and 

 Development in the Dependencies of the Falkland Islands. The analyses of the foetal 

 records suggest that the maximum time of pairing for Fin whales falls in about July, 

 for Blue whales between June and October, and for Humpbacks about September. 

 It is shown that though the existence of a definite pairing season is a clearly established 

 fact, it is prolonged over several months at least. It is inferred that parturition takes 

 place normally not later than July. 



These inferences, which are concerned with the breeding season of whales and drawn 

 from the whalers' records of foetuses, are subject to two weaknesses. In the first place, 

 the accuracy of the material is not wholly to be relied on. However, such inaccuracy as 

 exists does not seem to be sufficiently serious to affect the main conclusion that pairing 

 mostly occurs between about June and September, for this agrees well with similar 

 estimations from other sources, such as those of Hinton from the North Atlantic. The 

 more serious difficulty in fixing the maximum pairing season is due to the uncertainty 

 as to the rate of growth in the earlier stages of gestation, the uncertainty being due to 

 the fact that the information is derived only from records of foetuses measuring from 

 about I ft. upwards and is unchecked by observations on the ovaries and testes and the 

 evidence of minute foetuses. 



An exhaustive paper has recently been published by Risting (1928) in which 

 an analysis has been made of the statistics supplied by various whaling companies over 

 a number of years and assembled by the Norwegian Whalers' Association. This is 

 carried out on very much the same lines as Harmer 's work described above. The 

 paper serves in general to confirm the supposition that the period of gestation in Blue 

 and Fin whales is in the neighbourhood of a year, that pairing takes place during the 

 southern winter and that the pairing season is itself somewhat indefinite and prolonged. 

 It is estimated that among Blue whales pairing takes place mostly in June, July and 

 August, and among Fin whales in June, July, August and September. Risting's results 

 are, of course, liable to the same two weaknesses which are mentioned in connection 



