METABOLISM 303 



Cetaceans have, after all, no means of taking shelter or of standing in a 

 breeze when they get too hot, and above all, they cannot lose surplus heat 

 by perspiring, by lolling their tongues, or by increasing their rate of 

 respiration. Moreover, their skin is not as vascular as that of most mammals 

 which, in some parts of the body (e.g. the ears), can give off a great deal 

 of heat direct through the blood. In Cetaceans, the vascular system, as we 

 have seen, has a heat-preserving structure, and the animals must mainly 

 rely on the blood in the fins for liberating heat. According to Tomilin, 

 however, the blood flow to the fins of a dolphin can be so increased that 

 their temperature may be up to i6° F. higher than that of the flanks. 

 Whalers maintain that whales bleed from the tail fin much more profusely 

 after a long hunt than when they are killed quickly. Moreover, the 

 circulation to the skin is probably diverted to the small veins encircling 

 the arteries whenever heat is to be preserved, while this path is short- 

 circuited when heat is to be lost (see p. 298 and Fig. 172). The fact that 

 Cetaceans can, nevertheless, become too hot with serious consequences, 

 appeared clearly during the transport of Bottlenoses and other dolphins 

 from the coast to inland aquaria. Whenever their captors omitted to keep 

 their entire bodies moist with cold water, the animals' temperature rose 

 to as much as 108-5° F-, and they died. 



However, Cetaceans have one advantage over most terrestrial mammals : 

 their environment, though cold, is usually of even temperature. Diurnal 

 temperature differences, which are particularly marked in deserts and on 

 mountains, do not affect deep water to any great extent, and even the 

 temperature differences between the various layers are nothing like those 

 terrestrial mammals have to contend with. Even the temperature 

 differences between tropical and polar seas are no greater than 45° F. - 

 very much less than the seasonal fluctuation of up to 1 30° F to which a polar 

 fox or hare is exposed. Moreover, the food of migrating Cetaceans is so 

 distributed in the world's areas as to assist their thermal economy. In the 

 cold polar seas the animals can increase their blubber by feeding off a rich 

 and plentiful diet, while in the tropics, where food is mostly scarce, their 

 girth decreases and a far greater amount of heat is lost. This explains why 

 the Sei Whale, which lives largely in warmer waters and which is the 

 fastest swimmer of all Rorquals, has the thinnest blubber, while the slow 

 Greenland Whale which never leaves the Arctic has the thickest blubber 

 coat of all. 



From what has just been said, we may safely infer that Cetaceans have 

 a very high metabolic rate, which enables them to keep in constant motion 

 and thus to maintain their temperature. Even in their sleep they do not 

 keep perfectly still (see Chapter 6) nor do they seem to sleep for long 

 periods, particularly in cold waters. In warmer waters they can, of course. 



