Shark Facts: Habitat, Behavior, Diet (2024)

There are several hundred species of sharks, ranging in size from less than eight inches to over 65 feet, and native to every marine environment around the world. These amazing animals have a fierce reputation and fascinating biology.

Description

Acartilaginous fishhas a body structure formed of cartilage, instead of bone. Unlike the fins of bony fishes, the fins of cartilaginous fish cannot change shape or fold alongside their body. Even though sharks don't have a bony skeleton like many other fish, they are still categorized with other vertebrates in the Phylum Chordata, Subphylum Vertebrata, and Class Elasmobranchii. This class is made up of about 1,000 species of sharks, skates, and rays.

Sharks' teeth don’t have roots, so they usually fall out after about a week. However, sharks have replacements arranged in rows and a new one can move in within one day to take the old one’s place. Sharks have between five and 15 rows of teeth in each jaw, with most having five rows. A shark has tough skin that is covered by dermal denticles, which are small plates covered with enamel, similar to that found on our teeth.

Species

Sharks come in a wide variety of shapes, sizes and even colors. The largest shark and the largest fish in the world is the whale shark (Rhincodon typus), which is believed to reach a maximum length of 65 feet. The smallest shark is thought to be the dwarf lantern shark (Etmopterus perryi), a rare deep-sea species which is about 6 to 8 inches long.

Habitat and Range

Sharks are found from shallow to deep sea environments, in coastal, marine and oceanic environments the world over. Some species inhabit shallow, coastal regions, while others live in deep waters, on the ocean floor and in the open ocean. A few species, such as the bull shark, move easily through salt, fresh and brackish waters.

Diet and Behavior

Sharks are carnivores, and they primarily hunt and eat fish, sea mammals like dolphins and seals, and other sharks. Some species prefer or include turtles and seagulls, crustaceans and mollusks, and plankton and krill in their diets.

Sharks have a lateral line system along their sides which detects water movements. This helps the shark find prey and navigate around other objects at night or when water visibility is poor. The lateral line system is made up of a network of fluid-filled canals beneath the shark’s skin. Pressure waves in the ocean water around the shark vibrate this liquid. This, in turn, is transmitted to jelly in the system, which transmits to the shark’s nerve endings and the message is relayed to the brain.

Sharks need to keep water moving over their gills to receive necessary oxygen. Not all sharks need to move constantly, though. Some sharks have spiracles, a small opening behind their eyes, that force water across the shark’s gills so the shark can be still when it rests.

Sharks that do need to swim constantly have active and restful periods rather than undergoing deep sleep like we do. They seem to be “sleep swimming,” with parts of their brain appearing less active while they remain swimming.

Reproduction and Offspring

Some shark species are oviparous, meaning they lay eggs. Others are viviparous and give birth to live young. Within these live-bearing species, some have a placenta just like human babies do, and others do not. In those cases, the shark embryos get their nutrition from a yolk sac or unfertilized egg capsules filled with yolk.

With the sand tiger shark, things are pretty competitive. The two largest embryos consume the other embryos of the litter.

While nobody seems to know for certain, it has been estimated that the whale shark, the largest shark species, can live up to 150 years, and many of the smaller sharks can live between 20 and 30 years.

Sharks and Humans

Bad publicity around a few shark species has doomed sharks in general to the misconception that they are vicious man-eaters. In fact, only 10 out of all the shark species are considered dangerous to humans. All sharks should be treated with respect, though, as they are predators, often with sharp teeth that could inflict wounds (especially if the shark is provoked or feels threatened).

Threats

Humans are a greater threat to sharks than sharks are to us. Many shark species are threatened by fishing or bycatch, which leadto the deaths of millions of sharks each year. Compare that to shark attack statistics—while a shark attack is a horrifying thing, there are only about 10 fatalities worldwide each year due to sharks.

Since they are long-lived species and only have a few young at once, sharks are vulnerable to overfishing. Many are caught incidentally in fisheries targeting tunas and billfishes, and a growing market for shark fins and meat for restaurants is also impacting different species. One threat is the wasteful practice of shark-finning, a cruel practice in which the shark's fins are cut off while the rest of the shark is thrown back in the sea.

Conservation Status

The International Union for Conservation of Nature (IUCN) has assessed over 60 species of pelagic sharks and rays. About 24 percent are classed as Near Threatened, 26 percent are Vulnerable, and 6 percent Endangered on a global basis. About 10 are classed Critically Endangered.

Sources

• Camhi, Merry D. et al. "The Conservation Status of Pelagic Sharks and Rays: Report of the IUCN Shark Specialist Group Pelagic Shark Red List Workshop," Oxford, IUCN, 2007.
• Kyne, P.M., S.A. Sherrill-Mix, and G. H. Burgess. "Somniosus microcephalus." The IUCN Red List of Threatened Species: e.T60213A12321694, 2006.
• Leandro, L. "Etmopterus perryi." The IUCN Red List of Threatened Species: e.T60240A12332635, 2006.
• Pierce, S.J. and B. Norman. "Rhincodon typus." The IUCN Red List of Threatened Species: e.T19488A2365291, 2016.
• "Shark Facts." World Wildlife Fund.
• Simpfendorfer, C. & Burgess, G.H. "Carcharhinus leucas." The IUCN Red List of Threatened Species: e.T39372A10187195, 2009.