Shark Anatomy

Hydrodynamics and Performance

A famous aircraft-builder was fond of saying that "a good plane is a plane that is nice to look at", alluding to the parallel between aerodynamic performance and aestheticism.  In the same way we could say that a good marine predator is an animal with harmonious structure.  Any diver who has seen a shark at least once in his or her life has been struck by the purity of its lines and the suppleness of its movements, which make it unquestionably the best endowed of fish for slow or rapid swimming, acceleration or pursuit, cruising or hunting.  Here again the shark's adaptation to its environment is flawless, in the streamlining of its body, the size and the positioning of its fins, and the shape and proportion of its tail.

If the basic principles of aerodynamism and hydrodynamism are the same, water is nevertheless eight hundred times denser than air, and the shark's propulsion necessitates a locomotive power which is much more considerable in equivalent weight than that of a bird of prey in the air.

The first parameter to be set for any aquatic animal is that of its buoyancy, which must be variable at minimal energy costs.  So the bony fish possess an inflatable swimbladder, and the sharks have acquired - during the course of evolution - an extremely sophisticated double adaptation.  The first adaptation transformed these bony fish into cartilaginous fish, replacing the solid bony frame with a cartilaginous skeleton.  This development might seem regressive in comparison with the animal world as a whole were it not doubly beneficial:

• The gain in weight contributes to a reduced general density.
• The gain in elasticity permits more supple and less "jerky" swimming, and faster acceleration owing to a greater capacity of movement.

The second adaptation is the acquisition of a very large liver, proportionately the biggest in the animal world, to the point where one wonders whether it is this factor that determines the overall length of the body.

This liver is all the more imposing the nearer to the surface preferred habitat of the species in question is, and/or the more its pectoral fins are reduced in size.  As in an aircraft, if the surface area of the "midships frame" of the body is doubled, the surface area of the fins will have to increase by more than twofold, just as the wing surface has to compensate the fuselage section. ----