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Sharks are fish. Some people mistake sharks for mammals because they share certain physical traits. But like other fish, sharks are cold-blooded, breath through gills, and their bodies are covered in denticles (tooth-like scales). Sharks are also missing several key mammalian traits: They don’t grow hair, produce milk, or have a neocortex (part of the brain involved in perception and thought, among other things).
Sharks can be found in every ocean in the world. Some stick to the coasts and shallow waters, and others prefer the deeper waters in the middle of the ocean.
There are more than 500 species of sharks swimming in the oceans today, which are split across eight orders: Carcharhiniformes; Hederodotiformes; Hexanchiformes; Lamniformes; Orectolobiformes; Pristiophoriformes; Squaliformes; and Squatiniformes.
Nearly all sharks are carnivores that feed on other animals. Most sharks have fish, mollusks, and crustaceans on the menu, and they typically swallow their food whole. Larger species also consume bigger fish and marine mammals like dolphins and sea lions by ripping through their flesh. Filter feeders, such as whale sharks, gulp big mouthfuls of water and sift out plankton, shrimp and small fish using modified gills.
There’s a huge range! Whale sharks hold the record for the sharks with the highest tooth count; their mouths are brimming with 3,000 tiny, pointed teeth. Great white sharks, on the other hand, have only around 50 teeth.
Did you know: Sharks continuously shed and replace their teeth throughout their lives.
Sharks do not have bones. They have a skeleton made of soft cartilage rather than bone. Because cartilage is more flexible and lighter than bone, it helps sharks maneuver in the water and minimizes the energy they need to spend while swimming.
Most sharks cruise around the ocean at a leisurely pace of between one and three kilometers per hour (between 0.5 and two miles per hour), which is similar to average human swimming speeds. But there are several super-speedy species. The fastest-known shark species—the shortfin mako shark—has been clocked at a whopping 74 kilometers per hour (45 miles per hour) during short swimming bursts.
Most sharks live 20 to 30 years in the wild, but some species can live far longer. At the extreme end of the longevity scale are Greenland sharks, which can live at least 272 years, making them the longest-lived vertebrates (backboned animals) in existence.
Until very recently, it was assumed that sharks don’t sleep because they have to constantly swim to pass water over their gills and extract the oxygen. But not all species use this method of breathing; some use the muscles in their mouths to pump water over their gills, which allows them to breathe even when they’re resting. Recent research has confirmed that New Zealand’s draughtsboard sharks—a mouth-breathing species—do in fact fall asleep during their resting periods… sometimes with their eyes open!
Unlike some fish, sharks are internal fertilizers meaning the egg and sperm come together inside of the female’s body. Some sharks lay fertilized eggs on the ocean floor, and others give birth to live young (called pups).
Fun fact: Even though sharks’ go-to reproductive strategy is sex, a few rare cases of “virgin births” have been documented in which females become pregnant without any males around.
Humans kill an estimated 100 million sharks every year. That’s an average of almost 274,000 sharks every day, over 11,000 sharks every hour, and around three sharks every second!
In contrast to the staggering number of human-induced shark deaths, fewer than 10 people worldwide are killed each year by shark attacks. For context, every year approximately 24 people die after being hit by flying champagne corks; toasters kill an estimated 700 people, and lightning strikes and kills around 2,000 people.
Did you know: Experts believe these attacks on humans are usually unintentional. They are most likely cases of confused sharks mistaking kicking feet for small fish.
More than one third of shark species are currently threatened with extinction. Populations of sharks in the open ocean have declined by 71% over the past 50 years.
Much of these declines are due to global demand for shark meat and fins, pushing some shark species to the brink of extinction.
Meanwhile, sharks are rapidly losing their homes. Shark habitats, particularly the ones near the coasts, are being destroyed by residential and commercial development, cutting down of mangrove forests, and pollution.
Sharks are particularly vulnerable to all of these threats because they take such a long time to reach sexual maturity and most only have a few pups at a time. Many sharks wind up getting killed before they have a chance to reproduce, making it hard for their populations to rebound.
IFAW partners with governments participating in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to help limit the trade on shark species at greatest risk of extinction. IFAW’s current projects include providing training on how to enforce trade prohibitions, offering training on how to identify listed species visually and genetically, and helping to develop sustainable export quotas. Learn more about how IFAW is helping sharks.