268 



DISCOVERY REPORTS 



Table XXIV. Sei whale. Growth coefficients 



In the present species the only measurement with a conspicuously increasing relative 

 growth rate is likewise that of the anterior part of the head, so that in it, too, the mouth 

 and feeding mechanism becomes relatively larger with increasing total length. But an 

 increasing relative growth rate is not found in any similar degree in any of the other 

 parts, and this is perhaps to be explained by the smaller total size reached by the Sei 

 whale. Owing to its smaller size the body volume is proportionately very much less 

 than in the other species, and consequently a proportionately much smaller baleen 

 apparatus is able to capture a supply of food sufficient for supporting it. It seems 

 doubtful whether it can be said that the kind of food consumed by the Sei whale accounts 

 for the differing proportions, because, although the Sei whale feeds at times on very 

 much smaller plankton than the other species and its baleen appears to be specially 

 adapted for it, in the Antarctic and sub-Antarctic regions it has always been found to 

 be feeding on the same krill that is eaten by the other species. 



MIGRATION 



In the South Georgian whaling returns the occurrence of the Sei whale is always 

 almost entirely restricted to the months of February, March and April. Fig. 105 is a 

 typical unimodal graph of the numbers of whales taken during the seasons 1927-8 to 

 1930-1 inclusive, plotted by months. Harmer (193 1) gives a graph of the occurrence 

 of 1318 individuals during the sixteen seasons 1913-14 to 1928-9, which is essentially 

 similar: 93-1 per cent of the whales occurred in these three months and only 6-9 per 

 cent in the rest of the year. 



