Sharks Food

Sharks and rays have a very varied diet. They are carnivores which means that they eat animals rather than plants and algae. Some sharks commonly eat bony fishes, crustaceans (crabs, lobsters, and other animals with an external skeleton), mollusks(snails, sea slugs, octopus and squids), and different types of worms.

A shark’s diet is often determined by its habitat. For example, sharks that live out at sea (pelagic sharks) are more likely to eatfish and squid because that is all that is available.

Sometimes sharks change their diet as they get older. The Great White Shark mainly eats fish when it is young but once it reaches maturity it consumes more marine mammals like seals and sea lions.

Most sharks prefer live food but they will also consume carrion (dead fish and other animals) that they find on the sea floor.

Just like filter feeding whales, there are a few sharks that live by filtering plankton from the water. The filter feeding sharks may consume phytoplankton (microscopic plants and algae) while hunting for more nourishing zooplankton (tiny animals and larvae that drifts around on the currents). Ironically, the Whale Shark which is the largest fish in the sea, lives on plankton which is one of the smallest animals. So does the second largest fish; the Basking Shark. Although these sharks have huge mouths, their throats are tiny and they are unable to eat anything larger than a grapefruit. Their teeth which are no longer needed for feeding, have become very small.

The largest ray (the Manta Ray) is also a plankton feeder. It has a flexible projection on each side of its mouth called cephalic lobes that it uses to funnel plankton towards its mouth.

Most rays eat small fishes and benthic invertebrates; crabs, snails, and worms etc. that live on or under the sand.

Sometimes its possible to tell what type of food a shark eats by the shape of its teeth. Sharks that catch fast swimming fishes tend to have very pointed teeth that help them grasp the fish. Sharks that eat hard shelled animals have flattened teeth that form a plate to help them crush the creature’s shell like a nutcracker.

Tiger Sharks have a reputation for eating anything. They have been found with all sorts of strange things in their stomachs from clothes to license plates. Tiger Sharks have very sharp serrated teeth that are strong enough to bite through the shells of marineturtles.

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Sharks are different with other fishes

Sharks and rays do not have true bones like other fishes. They have cartilage instead which is lighter and much more elastic and allows them to bend in very tight circles.
Sharks do not have swim bladders. A swim bladder is a gas filled sack inside the body of bony fishes that allows them to stay still without sinking. Sharks compensate by having a very big liver that is filled with oil. Even so, sharks sink unless they keep swimming forward. The exception is the Sandtiger Shark which swallows air to make itself more buoyant.
A shark’s upper jaw is not fused to its skull like most animals. When a shark bites a large object, it is able to move its upper and lower jaw forward in order to take a bigger bite.
Unlike other fishes, sharks are able to replace their teeth constantly. New teeth grow from the inner surface of the jaw and rotate forward when the old teeth get worn out or lost during feeding.
Sharks and rays do not reproduce like other fishes. Most fish release clouds of sperm and eggs into the water column where they mix together. The fertilized eggs then float around until the fish larvae hatch and form schools of tiny fish. Male sharks have two organs called claspers attached to their anal fins. They insert one of these into the female shark’s cloaca (the entrance to the uterus) to transfer sperm (just like in mammals). Some sharks and rays incubate the eggs in their uteruses until the baby sharks are ready to be born. Other sharks and rays (i.e. skates) lay eggs and attach them to the reef.
Sharks have between 5 and 7 gill slits on each side of their body in front of their pectoral fins. Bony fishes only have one pair. Having many exposed gill slits probably helps transfer more oxygen into their blood faster which allows them to swim very fast when they need to.
Most shark’s skin is covered in small denticles instead of scales. Denticles are a lot like teeth. They have dentine in the centre and enamel on the surface. This makes shark’s skin very tough and abrasive like sandpaper. The shape and position of some shark’s denticles also helps reduce friction so that they can slip through the water easier.
Sharks have an extra sense that is able to detect tiny electric fields. They can use this to find food that is buried or to search for animals to eat in the dark or in turbid water.
Sharks and rays make up the sub-class of fishes called elasmobranches. This sub-class is part of a class of cartilaginous fishes called Chondrichthyes which also includes chimaeras (ratfishes).

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Shark Existence

The shark existence of the east coast of the USA decreased in the last 15 years substantially. The number of the hammerhead sharks sank around 89%, those of the thresher sharks around 80%, those of the great white sharks around 79%. The populations of the mako sharks, blue sharks and tiger sharks sank around 40-65%. The existence of the sandbar sharks were reduced in the last 10 years by overfishing by 85-90%.
Canadian researchers announce a decrease of the oceanic whitetip shark by around 99%. They are almost extinguished in certain regions already.

Sharks are not only caught actively for their meat, fins or cartilages. Millions of sharks die as non-usable catch (bycatch) in the nets and longlines of the swimming fish factories.

In the year 1991 the longline fishery brought in 8.3 million sharks world-wide. It is assumed that about half of it were blue sharks. More than 87% of these 8.3 million sharks were thrown away!

In the USA, along the Atlantic Coast and the Gulf of Mexico, annually approx. 2.5 million sharks are fished by sportfishing (game fishing). From that approx. 20-40% (500’000 – 1’000’000 sharks) got killed.

The population of all sorts of sharks is worldwide extremely threatened. In total 82 shark and ray species are registered on the so called “Red List” of the World Conservation Union.

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