THE SEI WHALE 27, 



from warmer waters and so is late in arriving on tlie South Georgian grounds? A 

 further possibihty may be that the distribution of whales is directly influenced by sea 

 temperature, a supposition in support of which some evidence is accumulating. Sei 

 whales in general frequent warmer waters than the Blue and Fin whales, and it is 

 possible that they approach South Georgia only when the temperature is high enough. 

 Maximum temperatures are reached in South Georgian waters in March, as shown by 

 Fig. 106 constructed from figures kindly supplied by Dr G. E. R. Deacon. Comparison 

 of Figs. 105 and 106 shows an appearance of direct correlation. 



Turning now to the returns from the South African whaling stations, Figs. 107 and 

 108 show the season graphs for Cape Province and Natal respectively for a number 

 of seasons. Fig. 107 shows three peaks, but is really to be regarded as bimodal because 

 an inspection of the figures from which it is constructed shows that in each season there 

 are only two peaks, but that in some seasons the second peak appears later than in 

 others. The two peaks in the autumn are thus due to combining the figures for several 

 seasons and must be taken together as representing one peak in the autumn in any one 

 season. The graph, then, is markedly bimodal and shows a northward migration in 

 May and a return southward in any of the months from August to October. Farther 

 to the north on the west coast of Africa the figures from Angola show only a unimodal 

 curve, indicating that the main body of the whales does not pass on beyond this point. 



The curve in Fig. 108 for Natal is unimodal with its peak in June. A peak in this 

 month would be expected from a consideration of Fig. 107, for the whales may be 

 expected to be about a month later in arriving so far up the East coast after they have 

 been in the neighbourhood of the Cape in greatest numbers in May. But the absence 

 of any second peak in later months is unexpected. Natal cannot represent the most 

 northerly point reached in the northward migration, because if it did the peak would 

 occur later in the season, in July and August. The only explanation of the unimodal 

 curve appears to be that the whales pass through the Natal grounds on their way north, 

 but that on their return migration they do not, probably keeping far off shore, out of 

 reach of the whalers, when on their way south. 



Comparison of these figures with Fig. 78 shows that the main season for parturition 

 and pairing occurs while the whales are in the waters north of Cape Province. The 

 breeding season is, however, widely spread through the months of May to August 

 inclusive, so that parturition and pairing are taking place during the whole of the 

 time that the species is migrating up the coast of Africa and back again. It would 

 appear that the widespread breeding season in this species is, partly at least, correlated 

 with the fact that Sei whales do not occur so near the pole as other species, and conse- 

 quently the migration is not so extensive to the south, though towards the equator they 

 appear to go as far as any species, and occur in the returns from the French Congo 

 and Ecuador. 



A further point to be noted with regard to this species is that its occurrence in 

 African waters is frequently very irregular in successive seasons; in some years it appears 

 plentifully and in others it is conspicuously scarce. No explanation of this phenomenon 



