THE SEI WHALE 



277 



SUMMARY 



This report discusses data from two hundred and twenty Sei whales examined at 

 the southern whahng stations by the staff of the Discovery Committee. 



The extensive statistics in the British Museum (Natural History) relating to whaling 

 have also been used in conjunction with the data collected by the committee. 



The sex ratio of the Sei whale shows that males comprise about 60 per cent of the 

 population. This proportion appears to be constant from an early stage of foetal life, 

 though it is obscured in the whaling returns by the high proportion of the larger females 

 selectively captured by the whalers. 



A series of standard measurements was carried out on the whales and the resulting 

 figures are discussed. The body proportions of the southern Sei whales are established, 

 and their range of variation is recorded. As far as comparative evidence is available 

 there is no indication of structural differences between the Sei whales of the northern 

 and southern hemispheres, the Atlantic or Pacific oceans. 



The rather wide range of variation in the colour of the species is described, and a 

 tendency towards asymmetrical coloration in a small proportion of the whales is 

 recorded. 



Hair appears in this whale on the upper part of the head, the ramus of the jaw and 

 on the chin. The numbers and distribution of the hairs are recorded. 



The arrangement of the ventral grooves in the Sei whale differs from that in the 

 Fin and Blue whales in that at their posterior end the grooves stop well anterior to the 

 umbilicus. They vary in number from forty to sixty-two. 



The baleen is very fine in texture and nearly black in colour. A number of white 

 plates commonly occur near the anterior end of the series and are frequently associated 

 with an adjacent white splash on the darkly pigmented snout. By plotting the baleen 

 length against the total length of the whale it is judged that weaning occurs when the 

 calf is 8-9 m. in length. 



The external characters of the southern Sei whales, like the body proportions, do 

 not appear to differ materially from those of northern Atlantic or Pacific examples of 

 the species. 



The food of Sei whales at South Georgia is exclusively krill, Eiiphausia siiperba, but 

 off the coasts of Africa smaller planktonic Crustacea are sometimes taken. Nearly all 

 the whales at South Georgia were feeding, but very few off South Africa. 



The thickness of the blubber in Sei whales from South Africa is less than in those 

 from South Georgia. This difference is more marked than in other species of whale 

 that have been examined. The present species does not show the marked improvement 

 in fatness towards the end of the season at South Georgia that is shown by larger 

 species. Immature Sei whales of both sexes are constantly fatter than mature ones. 

 Pregnant females are fatter and lactating ones thinner than the average. 



Large external parasites are very uncommon on Sei whales. A few Penella, and a 

 cirripede, only have been noted. Balaenophilus very commonly infests the baleen, as 



