300 WHALES 



detailed study of this question, even the composition of the bkibber changes 

 from part to part. Thus \vhile its average fat content is 60 per cent in 

 Rorquals and 45 per cent in Sperm Whales^ the remainder being connec- 

 tive tissue, a separate analysis of individual parts of the body shows that 

 the fat content of the blubber is much greater on the dorsal than on the 

 ventral side, ^vhere, in turn, it is greater than on the flanks. The fat 

 content increases perceptibly from snout to tail - on the dorsal side from 

 55 per cent to 80 per cent, and on the ventral side from 34 per cent to 

 72 per cent. In general, we may say that the thicker the blubber the fatter 

 it is and the less it consists of connective tissue. 



In Rorqual embryos the relative thickness of the blubber increases 

 throughout the period of gestation, right up to birth. In Blue and Fin 

 Whales, its thickness is 0-75 per cent and o -6 per cent of the total length 

 of the embryo respectively, the corresponding figures in adult specimens 

 being 0-53 per cent and 0-46 per cent. On the other hand, the fat content 

 of embryonic blubber is only 5-6 per cent. Apparently, the blubber begins 

 as a 'skeleton' of connective tissue which becomes fattier after birth. This 

 is not so strange if we bear in mind that the embryo or foetus has no need 

 of fat as reserve food or as insulation against cold. 



In adult Rorquals the relative thickness of the blubber increases with 

 body length - hence the difference of roughly 14 per cent in the relative 

 thickness of the blubbers of Blue and Fin Whales, Blue Whales being 

 roughly 14 per cent longer than Fin Whales. It seems likely that smaller 

 animals which have a relatively larger skin surface, and thus greater heat 

 losses, must use a larger percentage of their food intake for preserving 

 thermal equilibrium by combustion. Moreover, measurements have shown 

 that pregnant cows have the thickest blubber, while lactating cows have 

 the thinnest. Clearly, during gestation a reserve is put by against the time 

 when the suckling calf will make heavy demands on its mother (see 

 Chapter 13). During the winter season the thickness and the fat percentage 

 of the blubber of Rorquals decrease considerably. The thinnest animal 

 ever described was a sixty-five-foot female Fin Whale which ran aground 

 near Wilhelmshaven on 8th February, 1944. The thickness of much of its 

 dorsal blubber was no more than ij inches and its fat content varied 

 between i -7 per cent and 3-5 per cent. 



To get an idea of the insulating properties of blubber, we would have 

 to know the normal body temperature of Cetaceans. Now, it is extremely 

 difficult to take the temperature even of porpoises, let alone of big whales, 

 and we generally have to make do with measurements on freshly killed 

 carcasses. True, Zenkovich managed to take the temperature of a living 



^ In fact the layer of blubber of most Toothed Whales contains not fat but a wax-like 

 substance (see page 72). 



