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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]
Basking sharks have been shown from satellite tracking to overwinter in both continental shelf (less than 200 m or 660 ft) and deeper waters. [7] They may be found in either small shoals or alone. Despite their large size and threatening appearance, basking sharks are not aggressive and are harmless to humans.
Sharks do not have moveable upper or lower eyelids, but the tiger shark—among other sharks—has a nictitating membrane, a clear eyelid that can cover the eye. [32] A reflective layer behind the tiger shark's retina , called the tapetum lucidum , allows light-sensing cells a second chance to capture photons of visible light.
Many sharks can contract and dilate their pupils, like humans, something no teleost fish can do. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes. This membrane covers the eyes while hunting and when the shark is being attacked.
Sandbar sharks usually have heavy-set bodies and rounded snouts that are shorter than the average shark's snout. Its upper teeth have broadly uneven cusps with sharp edges. Its second dorsal fin and anal fin are close to the same height. Females can grow to 2–2.5 m (6.6–8.2 ft), males up to 1.8 m (5.9 ft).
Some sharks are so flexible, they can bend right around and touch their tails with their snouts. Shark skin is so rough that in the past it was used to make a type of sandpaper, called shagreen. Without their fins, sharks wouldn’t be able to stay the right way up. They’d roll over in the water. Most sharks never close their eyes.
The blind shark (Brachaelurus waddi) is one of two species of carpet sharks in the family Brachaeluridae, along with the bluegrey carpetshark (Brachaelurus colcloughi).Found along the coast of eastern Australia, this nocturnal, bottom-dwelling species is common in rocky areas and seagrass beds from the intertidal zone to a depth of 140 m (460 ft).
The Port Jackson shark is a nocturnal species which peaks in activity during the late evening hours before midnight and decreases in activity before sunrise. [2] A study showed that captive and wild individuals displayed similar movement patterns and the sharks' movements were affected by time of day, sex, and sex-specific migrational behaviour.