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Heat Exchange

One distinctive feature of the Lamnid sharks is that are able to elevate their body temperature above that of the ambient water. Through a counter-current heat exchange system, the temperature in the stomach, brain, eye and swimming muscles can be up to 13 C higher than its surroundings with its stomach remaining at about 25C. 

The white shark, along with six other mackerel shark species, is able to elevate parts of its body above that of the ambient water temperature, a process named regional endothermy. Through a counter-current heat exchange system, the temperature in the stomach, brain, eye and swimming muscles can be up to 13 C higher than its surroundings (Goldman, 1997) with its stomach remaining at about 25C (Roesch, 2001).  There is a significant positive correlation between muscle temperature and ambient water temperature but it appears that stomach temperature is the best indicator of core body temperature since it varies only slightly between both days and amongst individuals (Goldman, 1997).

This is accomplished by re-directing blood from enlarged arteries in the flanks inward through a dense network of small arteries and veins called the rete mirable. Through muscle contraction and metabolic processes, blood travelling to the heart in the veins in heated and this heat is transferred to the blood in the arteries as the blood vessels pass each other and cycled back to the muscles and visceral organs (Martin 2001). There are three sets of retia in the white shark, one in the swimming muscles, one in the anterior viscera and the final set surrounding the brain.

Being warm-bodied can be extremely advantageous as a 10C rise in body temperature can increase the speed of muscle contraction three-fold. This will allow increased power and more sustained and accelerated swimming speed, vital when pursuing prey or fleeing from predators (Roesch, 2001). It would also allow penetration into colder and deeper waters than otherwise possible whilst maintaining a high temperature in the brain in order to function effectively. If they did not possess this mechanism, they would be unable to actively search for and prey upon pinnipeds in the cool waters they inhabit (Goldman, 1997). Increased temperatures in the viscera will result in an increase in the digestion and absorption of large amounts of blubber thereby preventing the defecation of undigested material (Goldman, 1997). Finally, since the visceral retia also warm the uterus, the development of young will also be enhanced.

However, the costs of this endothermy are that a warm-bodied shark will need to ingest 10 times more food than its cold-bodied counterpart. This results in the requirement for energy-rich, large prey, most often found in the cooler temperate oceans of the world. Although the white shark is known to visit tropical waters, it is primarily a temperate water inhabitant to enable the exploitation of these productively rich waters. By extending their range into colder waters, the mackerel sharks are able to avoid competition for food from their cold-bodied cousins.