Sharks live in what type of water

Viviparity is when a shark nourishes her growing shark embryo internally and gives birth to a fully-functional live pup. These shark species, like the hammerheads Sphyrnidae , maintain a placental link to the embryo, similar to humans. In aplacental viviparity, also called ovoviviparity, there is no placental link. The most common type of reproduction in sharks, ovoviviparity occurs when the egg hatches while still inside the mother. Sand tiger sharks Carcharias taurus will actually eat their siblings in the womb.

Female sand tiger sharks often mate with several different males, producing a litter of shark pups from a number of fathers. Researchers think that the larger sharks will consume their smaller siblings that are not as closely related to prevent competition.

Other shark species release an egg case, where the developing embryo gains nutrients from a yolk. This is called oviparity. Typically sharks that live on the seafloor, like the swellshark Cephaloscyllium ventriosum , are oviparous. They attach their egg case to a rock or other hard surface, or wedge it into a safe spot on a sandy bottom or rocky area. Pacific white skates will attach their egg casings near the warmth of hydrothermal vents, potentially as a way to speed up the incubation process.

The egg case of most sharks is a leathery transparent brown, with slits on either side that allow water to flow through to replenish oxygen in the sac. The tiny shark moves around to help facilitate the water movement and, once the nutrients from the yolk sac are used up, the small shark makes it way out of the case to fend for itself.

You can find a shark that eats just about anything: the whale shark, the biggest fish in the sea, eats only tiny plankton, while the bonnethead shark gets some of its nutrition from seagrass, a type of underwater plant. Tiger sharks have even been found with license plates and nails in their stomachs. But most sharks are carnivorous and eat animals ranging from crustaceans like crabs to squid, fish and marine mammals like seals and sea lions.

Some sharks have even been found with giant squid beaks in their stomachs! Many sharks, however, have developed specific mechanisms that help that capture their prey. Some bottom dwelling sharks like wobbegongs also called carpet sharks hide and ambush their prey, sucking them up with small mouths. Some sharks swallow their prey whole, but others rely on very sharp teeth to break apart food—especially food larger than themselves.

The thresher shark Alopias genus has a long, tapered tail that is slaps into a school of fish to stun them and grab its meal. The whitetip reef shark Triaenodon obesus tends to hunt alone, sometimes chasing its prey into a crack and sealing the exit with its body. Sawsharks , meanwhile, get their name from their saw-like snout that is used to scrape up invertebrates from the seafloor and to stun fish.

The cookie-cutter shark Isistius brasiliensis is an especially unusual case. Although its name makes it seem like a Muppet, this shark is actually a quite intimidating creature that takes large round cookie-cutter shaped bites out of animals such as tuna, whales, dolphins, and seals.

They sneak up and suction onto larger animals and twist around to take a bite of flesh using their lower row of sharp teeth and tongue-like basihyal. There are also some large species of sharks that are plankton feeders. The basking shark, megamouth shark and whale shark all consume the tiny crustaceans. Their teeth are small and they have modifications on their gills that act like sieves to capture the plankton so they can swallow them in large gulps. Although scientists have yet to find a truly vegetarian shark, the bonnethead shark eats a substantial amount of leafy greens.

Inhabitants of seagrass meadows, the sharks chow down on crabs, shrimp, and fish and in the process also swallow the seagrass. Over half the shark's diet is seagrass , and they are about as efficient at absorbing nutrients from the seagrass as sea turtles, an almost completely herbivorous animal. Large sharks have few natural predators besides other sharks, although some small juvenile sharks are eaten by birds and large fish. Sharks are primarily killed by humans both intentionally and unintentionally as bycatch.

Because of sharks slow growth and low reproduction rates, the rate at which humans are killing sharks is endangering shark populations and ecosystems throughout the world. It's estimated that million sharks are killed every year by commercial and recreational fisheries. Until recently, fishermen and governments didn't keep very good track of official shark catches. Instead of reporting shark catches by species, they'd report all sharks together or even grouped sharks and rays together.

That makes it difficult to know how many sharks were fished historically. Regardless, today scientists estimate that one-quarter of shark species, along with their ray and chimaera relatives, are threatened with extinction according to the International Union for Conservation of Nature IUCN Red List criteria. Sharks are particularly vulnerable to overfishing. They grow slowly, reproduce late compared to other fishes, and don't have many offspring at once. Combined, these traits make them slow to replenish their populations when they are fished or otherwise killed at such fast rates.

A study comparing sharks and bony fishes found that sharks have twice the extinction risk of bony fishes. Some sharks are caught by fisheries targeting sharks specifically. Not all are caught intentionally, however. Sharks are often caught as bycatch—which means that, while the fishermen were trying to catch a different kind of fish, they accidentally catch sharks in their nets too. Some bigger open ocean-swimming sharks are caught by longline fisheries aiming for big fish like swordfish or tuna.

For example, large shark abundance decreased by 21 percent in the tropical Pacific after industrial fishing began in the s. The 90 percent of elasmobranchs sharks, skates and rays that live near the seafloor are particularly susceptible to fisheries that drag a net across the ocean bottom trawling. This can change local shark populations dramatically. For example, between and , after shrimping began in the Gulf of Mexico, some populations of shallow water sharks and ray species dropped by up to 99 percent.

Such a big change doesn't just affect the sharks, but also their prey and the rest of the ecosystem. See 'Ecosystem Effects'. Today, fins are the most valuable part of a shark. The targeted shark-fin fisheries around the world are trading the fins of roughly to million sharks every year according to a estimate.

Driving this trade is the demand for and consumption of shark fin soup in Asia. Historically shark fin soup was only affordable to the richest people, but as the middle class has grown, it has become a more mainstream menu item. Some of the shark fins used to make this soup are cut off and sold at market alongside the shark they came from. But many are cut off of live sharks, which are then thrown back into the ocean to save space on board for the more valuable fins to drown— a practice known as shark finning.

This practice is increasingly seen as cruel and wasteful, and around the world regulations are being put into effect to end shark finning. See 'Shark Protections' below. Sharks can play a large role in their ecosystems, no matter their size. Big predatory sharks require a lot of food. So the removal of too many large sharks can have a ripple effect on the populations of their prey: if you remove the sharks, too many prey are able to survive, and those then compete with one another and other animals for food, shifting the food web.

One of the types of prey that can be greatly affected by shark removal is smaller sharks and rays. Often, large sharks are among the only animals that eat small sharks.

And so when large sharks are overfished, researchers sometimes see an increase in smaller shark populations. For example, as large sharks were removed from the coast of New England in the s by fisheries, dogfish catch actually went up five-fold into the late s.

This suggests that dogfish were able to thrive once their predators disappeared. But then, as fisheries went after dogfish at higher rates, their populations dropped in turn. Large sharks also commonly prey upon sea turtles, seabirds and marine mammals; in fact, sharks are some of the few predators of large marine mammals. Because of this, their presence or absence can have a large effect on prey populations. The presence of tiger sharks in Shark Bay, Australia, for example, changes the behavior of sea turtles, dolphins and dugongs , which avoid shark-infested waters even when food is abundant there.

One place where shark numbers have definitely decreased is on coastal coral reefs around the world. Healthy coral reefs far from human settlements have many sharks —far more than their top predator counterparts like lions on land.

But when humans move in, sharks disappear unless they are protected. A recent study found that in the Pacific islands, shark density is only percent what it would be if no people lived in the area. Because humans have lived near reefs for so long, it's hard to know what these ecosystems should look like with a healthy number of sharks—and thus what effect the removal of sharks is having.

Recent studies of remote uninhabited islands show that top shark predators outnumber their prey , in some cases making up 50 to 80 percent of the biomass on a reef! They are able to maintain this ratio because of the speedy transfer of energy up the food chain. Shark populations have been in trouble for decades due to overfishing. In , the International Union for the Conservation of Nature IUCN Redlist released a report from its Shark Specialist Group that reviewed the status of 64 species of open ocean sharks and rays and found that 32 percent were threatened with extinction.

The report called on governments to increase protections of sharks through science based catch limits, end shark finning and improve monitoring and research, among other recommendations.

The law said that fishing vessels could not transport or possess shark fins without the corresponding shark body within miles of U. The fins could be separated from the animal aboard the ship, but the carcass must also be kept on board. However, there were several loopholes in the legislation that let people transfer fins on non-fishing vessels, and the sale and trade of fins were not addressed.

The law also was difficult to enforce. For example, regulators typically make sure fishermen aren't breaking this type of law through a shark fin conversion ratio. Measurements of the weight of shark fins are taken and compared to the weight of the remainder of the sharks; if the fins weigh more than an established ratio, it is presumed that illegal shark finning was taking place.

Under the Shark Finning Prohibition Act, the shark fin conversion ratio was 5 percent. But this method can be difficult to enforce PDF because the ratio of fin weight to body weight varies among shark species. As a result, illegal fishers are sometimes able to fake the fin ratio, leaving some shark bodies behind in the water while fooling regulators. In the Shark Conservation Act was signed into law. Hawaii was the first U.

In addition to finning bans in the U. These plans reflect the results of research, population assessments and work with fishermen. Additionally, two populations of scalloped hammerhead sharks were listed under the U. Endangered Species Act in July , making them the first sharks protected under the law. Reducing the accidental catching of sharks as bycatch has also been an important goal. In California, for example, the banning of nearshore gillnets has reduced shark mortality.

Similarly, changes in hook and fishing line design make it easier for sharks to escape and improve their ability to survive after their release when they are caught by mistake.

This led to the creation of the International Plan of Action for the Conservation and Management of Sharks, which was led by the FAO and implemented in after a series of workshops and consultations with shark experts. Countries that are a party to the United Nations participate in the International Plan of Action voluntarily. CITES also lists the basking shark, whale shark and great white shark under their Appendix II, which regulates their trade to protect the threatened species.

Six more shark and ray species were added to Appendix II in September Regional fisheries management organizations , such as the Northwest Atlantic Fisheries Organization NAFO and the International Commission for the Conservation of Atlantic Tuna, manage fish species that travel between international lines. They have various shark finning prohibitions and regulations among 17 geographic regions worldwide. Individual countries around the world have taken steps to protect sharks in the form of fishing regulations, shark finning bans, sale and trade bans, transport bans and shark sanctuaries where no or limited shark fishing is allowed.

Palau became the first country to implement a shark sanctuary in , banning all shark fishing in its , square miles of territorial water. Many countries have followed suit with various levels of protection. The Chinese government will no longer serve shark fin soup at official functions , and a number of hotels and supermarkets have pledged not to sell or serve shark fin products.

Even some airline companies are banning the transport of fins on their planes. You can see how efforts to protect sharks have spread through time in the animated map below. Demand for shark fins has dropped in some Asian markets, and some shark populations are slowly beginning to increase.

Humans have long had a fascination with sharks, portraying them in books, movies, TV shows and other media as violent human killers. Popular movies like Jaws and Sharknado have furthered our fear of sharks, despite the fact that millions of sharks are killed by humans every year and technically, you are more likely to be killed by a vending machine than a shark. But sharks rarely attack humans, at least not purposefully. Tiny sea creatures seek shelter among the rocks, and algae and coral flourish here.

This steady food supply attracts multiple species of sharks, including spiny dogfish sharks , white sharks and scalloped hammerhead sharks. Its sharp teeth and powerful jaws allow it to take bites from species much larger than itself. Sandy plains: The shallow regions that comprise most of the continental shelf are known as sandy plains.

These sandy, muddy areas support a wide variety of marine life, including small fish and crustaceans. Its jaws snap like a bear trap and make quick work of most small prey after a typical ambush. Gray reef sharks , Caribbean reef sharks and zebra sharks tend to live near coral reefs, feasting on the diverse marine life found in these communities. Zebra sharks have sleek bodies that can squeeze into coral crevices to hunt their prey.

They usually hunt at night and spend their days resting on the ocean bottom. In this region of the sea, fish tend to move about in large schools, and they can be difficult to catch. Sharks that live in the pelagic zone have adapted to become extremely fast-moving, able to catch their prey with swift movements. As Sutherland explains, sharks lack a swim bladder—the gas-filled organ that helps other bony fish float.

But they do have extra large livers , which provide some buoyancy and help keep them sinking to the ocean floor. But fresh water changes how much buoyancy the shark's liver can provide. The researchers found that when sharks swim in fresh water, they are two to three times less buoyant than when they swim in salt water. There are a few river sharks, like bow sharks , that have adapted to less salty environments; their livers, the study found, are less dense than those of marine sharks, which helps them stay afloat.