232 DISCOVERY REPORTS 



in width more quickly than in length between these total lengths, but the figures for 

 1 6 m. and above show a decrease. The data are insufficient to draw generalizations, but 

 the values for whales i6 m. and more in length may indicate the effects of wear in older 

 whales, in which a decrease in breadth, both absolute and expressed as a percentage of 

 length, may be produced by the inner edges of the plates becoming more and more 

 frayed out into bristles with increasing age and use. 



The spacing of the baleen plates was recorded in a number of whales. Fig. 62 shows 

 the spacing plotted against whale length and indicates an increase in spacing from 

 0-8 cm. in II m. whales to 1-5 cm. in 17 m. whales. These figures may be compared 

 with those of Blue whales, i •0-2-5 cm., and Fin whales i-o-i-8 cm. Here again the 

 reason for the fineness of texture of Sei whale baleen is shown, because the spaces 

 between the plates are not much less than in Fin whales, while the number of plates 

 is little less than in that species and the length of jaw is much smaller. The figures show 

 no difference between male and female or South African and South Georgian Sei whales. 



The length of the longest baleen plates is plotted against the total length of the whale 

 in Fig. 63. The plotted points show that the longest baleen plates vary from 35 cm. in 

 10 m. whales to 80 cm. in 17 m. whales. The growth curve obtained from these points 

 is shown as a solid line, while the dotted portion is obtained by analogy from the known 

 facts that occur in the Blue whale. This shows a gradual increase in baleen length 

 followed by a sudden spurt where it joins the solid line. The sudden spurt represents 

 the accelerated growth of baleen at weaning, when a diet of milk is changed for one of 

 krill : weaning probably takes place between the lengths of 8 and 9 m. 



NORTHERN AND SOUTHERN SEI WHALES COMPARED 



The descriptions given of the details of the external characters of the Sei whale from 

 South Georgia and South Africa do not indicate any specific difference from the 

 northern Sei whale (CoUett, 1886; Andrews, 1918) nor any differentiation into separate 

 southern races. Andrews (1918) gives an extensive description of the Sei whales taken 

 at Japan and shows that they do not differ even subspecifically from the Sei whales of 

 the North Atlantic described by Haldane (1904-10), Collett (1886) and Millais (1906). 

 Whales from these seas appear to be specifically identical with the present series, so 

 that the Sei whale is undoubtedly cosmopolitan. This is at variance with the view 

 expressed in 191 5 by Hinton (1925) that "it is highly improbable that the southern 

 Sei whale is identical with Balaenoptera borealis. The latter is a plankton-eating species 

 normally frequenting the eastern part of the north Atlantic from 20° N northwards." 

 From the limited material available to him he concluded that the southern Sei whale 

 was a little larger than the so-called Bryde's whale and smaller than the true Sei whale. 

 The figures of the present series, however, do not substantiate this, for they show that 

 the southern Sei whale is, if anything, a little larger than the Sei whale of the northern 

 hemisphere. This difference is doubtless due to a higher proportion of immature 

 specimens included in the figures of the northern catches. 



