LOCOMOTION AND LOCOMOTORY ORGANS 



99 



-i's, 



Blue Whale 



V 



Fin Whale 



Humpback 





Sperm Whale 



Figure §6. The most important clues for identifying various whales from the way in which 

 they surface. {Modified after Peters, igsS.) 



How do whales and dolphins manage to swim so fast and to manoeuvre 

 so skilfully? We know that, by and large, they swim like fish. In fish, too, 

 the pectoral fins are too small to aflfect forward motion, their function 

 being to help the animal to balance and steer, particularly when they 

 are fully extended. Propulsion of the body is brought about either by 

 flexions of the whole body, as is the case with shark and trout, or else by 

 flexions of the tail alone, as with many other fish. Now the whale's flukes 

 are in a horizontal plane, while those of fish are vertically placed, and 

 hence the whale's propulsion is clearly based on up and down motions of 

 the tail and not on lateral flexions, though Scoresby (1820) thought he 

 had detected horizontal motions also, during which the tail acted very 

 much like a ship's screw. On the whole, however, whales move their flukes 

 very much as frogmen move their flippers, though they do not, of course, 

 beat alternatively with right and left. 



Everyone who has watched a swimming whale or dolphin knows how 

 difficult it is to follow its movements accurately. Dolphins do not seem to 

 move their bodies at all, or at best show a small quiver, while big whales 

 so churn up the water surface that they become practically invisible. 

 Townsend, during observations of Bottlenose Dolphins in New York 

 Aquarium (1907) saw nothing apart from vertical tail motions, and True 

 fared no better with a captive Beluga. Russian investigators, e.g. Shuleikin 

 (1935) and Stass (1939), however, hold that not only are there undulations 

 of the whole body but that the tail acts like a screw, i.e. it moves hori- 

 zontally, as well as vertically. Shuleikin based his opinion on a film of a 



