Shark Anatomy

Respiration

The cruising speed of swimming can be maintained only if the oxygen supply to the muscles is correct.  Oxygen is extracted from the water in the region of the gills.  Sharks' gills are made up of cartilaginous arches supporting a series of gill rakers which are perpendicular to them.  These rakers in turn support secondary bars which are also perpendicular and direct the flow of water taken in through the mouth in the opposite direction to the blood flow.  Exchanges of oxygen and carbon dioxide between blood and water therefore take place all the more quickly.

The water taken in through the mouth is discharged through five gill slits in the majority of sharks (six or seven in the most primitive species, though nobody knows why).

The process can be accelerated in the fastest-swimming species through the "ramjet principle", in other words the exchange happens better the faster the shark moves.  Lamnidae sharks have to keep moving to ensure this process which means that if they stop they die from suffocation (this accounts for the majority of the big predators caught in beach-defense nets being brought up dead).

By contrast, some bottom dwelling species (dogfish, carpet sharks, etc.), with no regular movement, pump water by rhythmically contracting the muscles that control the inlet and outlet valves of the gill system.

Between these two extremes, certain species such as the Sand or Sand Tiger shark, also known as the Grey Nurse Shark (Eugomphodus taurus), are able to make use of both pumping and ramjet, achieving a real saving in energy.

To ensure a good transfer of oxygen from the gills to the muscles and other organs, a maximum percentage of red corpuscles in the blood (haematocrit) is needed.  In the benthic species living at great depths, the haematocrit is of the order of 15%, while it reaches 35% in the Lamnidae family, the most active species.

A final parameter for good oxygen transfer is the cardiac pump.  Unlike in mammals, there is no relationship between the heart size and the body weight or the activity of the animal.  The ratio of heart weight to body weight remains constant, of the order of 0.1% in all species, no matter how active.  Only the Lamnid sharks, including the Great White and the Mako, have a ratio reaching 0.2% to 0.3% (which gives a heart of only 4 kilos in weight for a monster of 2 tons).  This means that even these very large predators do not exhibit exceptional stamina in prolonged exertion, even though they are capable of enormous exertions in short bursts.

The spiracles are external openings of the respiratory apparatus of certain rays and sharks which, living on the bottom, make use of this in preference of their gills.

When big sharks are caught for aquaria, they are forcibly kept in an artificial current in order to "resuscitate" them, and to enable them to get over the shock of capture and transportation.

As already mentioned, when a shark gets caught up in a beach defense net - which exists in Australia and South Africa - its forced immobilization leads to a rapid fatal asphyxiation.  At the atomic power station in the Cape, sharks are sometimes caught in the suction gratings, the diameter of which is about 2 meters.  However in these cases they do not die, as a current of water is artificially maintained in their gills by the suction.  On the other hand, when special clasps are used to haul them to the surface, they die very quickly, their backs breaking under their own weight.