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Having the ability to keep their warmth helps them as predators as well. Another group of sharks, known as the mackerel sharks are able to warm their blood. These mackerel sharks retain their blood by using a heat exchange system called rete mirabile. The body temperature of mackerel sharks can be up to 10 o higher than the surrounding water. [10]
Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver filled with oil that contains squalene, and their cartilage, which is about half the normal density of bone. [33] Their liver constitutes up to 30% of their total body mass. [39]
Uncostumed humans, however, such as those surfboarding, light snorkeling or swimming, present a much greater area of exposed skin surface to sharks. In addition, the presence of even small traces of blood, recent minor abrasions, cuts, scrapes, or bruises, may lead sharks to attack a human in their environment.
Like many sharks, this sevengill is counter-shaded. Its dorsal surface is silver-gray to brown in order to blend with the dark water and substrate when viewed from above. In counter to this, its ventral surface is very pale, blending with the sunlit water when viewed from below. The body and fins are covered in a scattering of small black ...
Under normal circumstances, horn sharks are harmless to humans and can readily be approached underwater. [3] However, they can be provoked into biting, and some pugnacious individuals have been known to chase and bite divers after being harassed. [6] These sharks should be handled with care as their fin spines can inflict a painful wound. [3]
Few animals inspire the level of fear that sharks do, thanks to “Jaws” and other sensational tales of deadly encounters, and a steady stream of U.S. shark sightings has been the stuff of ...
Humans, 2 million years, even the ancestor of chimps and ourselves only takes it back to 6 million years ago, while sharks go back an incredible 450 million years.
In the ocean food chain, large sharks generally only have to worry about keeping orcas at bay — but a new study suggests the apex predators may have to watch out for their own.. Researchers have ...