- 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.
Filed under Sharks Knowledges · Tagged with algae, amp, animal, anything, Basking, basking shark, benthic, bite, bony, bony fish, bony fishes, car, carnivores, carrion, catch, Co, Crab, creature, crush, Determined, diet, drift, eatfish, EST, example, feed, feeder, feeding, filter, fin, fish, fish in the sea, floor, food, form, grapefruit, Great, great white shark, habitat, hunting, largest fish, larvae, license, lobster, lot, Mammals, Manta, manta ray, Marine, marine mammals, maturity, mean, microscopic plants, mollusks, mouth, need, nutcracker, pelagic sharks, phytoplankton, plankton, plankton feeder, plate, point, project, projection, range, rat, rate, ray, reach, reputation, round, sand, sea, sea floor, sea lions, sea slugs, seal, seals and sea lions, shape, shark, Sharks, shell, side, skeleton, skin, small fishes, squid, swimming, term, They are carnivores, thing, tiger, tiger shark, Tiger Sharks, time, tiny animals, turtle, type, US, use, vertebrate, water, Whale, whale shark, what are sharks eat, White, white shark, With, zooplankton
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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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Sea Shepherd is best known for its frontline work protecting marine mammals but its broader mandate is to protect all ocean creatures. Styled on the more widely publicized organization Greenpeace, Sea Shepherd continued to grow teeth where Greenpeace lost them through inactivity. Sea Shepherd’s founder Captain Paul Watson has a reputation for pursuing illegal whalers and longliners, harassing seal cullers, organizing rallies, and generally irritating governments that would rather turn a blind eye, and infuriating fishing consortiums who would rather go about their illegal and often cruel practices unnoticed.
Sea Shepherd’s flag ship The Farley Mowat has harassed shark fishing boats in Costa Rican waters and sent sailors sprawling over their decks after being hit by The Marley Mowat’s water cannons.
Captain Watson also manages to fit a lecture circuit into his busy schedule, during which he educates anyone willing to listen on the plight of whales, dolphins, seals, and sharks.
Sea Shepherd’s second vessel is on permanent patrol in the Galapagos area where Park Rangers are virtually helpless against the Ecuadorian fishing boats that brazenly ignore the protection afforded to the park by its world heritage site status. Even with Sea Shepherd’s vigilant patrols the rangers are so out numbered that fishermen have an almost unimpeded run of the islands and the Galapagos Sharks that once schooled in vast numbers around Darwin Island have all but vanished.
This kind of hard line activism is not for everyone. The Sea Shepherd crew have been deported, locked up, threatened, and roughed up on many occasions. Violent confrontations at sea may not fit with your particular code of behavior or ethics but what makes you more uncomfortable: sponsoring Sea Shepherd’s activities that achieve direct results in the protection of endangered creatures, or lobbying deaf government officials while the wholesale slaughter of our oceans sharks and whales continues unchallenged?
If Sea Shepherd seems like a worthwhile organization with which to take a stand, you can help them in a variety of ways. Joining Sea Shepherd with a modest contribution, helps with the provisioning, fueling, and maintenance of their ships. As a member you may also have the chance to sign on as a volunteer for a tour of duty on one of their campaigns. On their website they list what skills they are looking for in new crew members but they also take unskilled deckhands that are willing to work hard.
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The dark markings indicate gene expression in the electrosensory organs in the head of an shark.
Gainsville, Florida (Feb 6 2006 18:53 EST) Sharks are known for their almost uncanny ability to detect electrical signals while hunting and navigating.
Now researchers have traced the origin of those electrosensory powers to the same type of embryonic cells that gives rise to many head and facial features in humans.
The discovery, reported by University of Florida scientists in the current edition of Evolution & Development, identifies neural crest cells, which are common in vertebrate development, as a source of sharks’ electrical ESP.
It also fortifies the idea that before our early ancestors emerged from the sea, they too had the ability to detect electric fields.
“Sharks have a network of electrosensory cells that allows them to hunt by detecting electrical signals generated by prey,” said Martin Cohn, a developmental biologist with the departments of zoology and anatomy and cell biology, and the UF Genetics Institute. “That doesn’t mean they can only detect electric fish. They can sense electricity generated by a muscle twitch, even if it’s the weak signal of a flounder buried under sand.”
Likewise, sharks are widely thought to use the Earth’s magnetic field for navigation, enabling them to swim in precise paths across large expanses of featureless ocean, Cohn said.
“If you think of this in the big picture of evolution of sensory systems, such as olfaction, hearing, vision and touch, this shows sharks took a pre-existing genetic program and used it to build yet another type of sensory system,” Cohn said.
UF and University of Louisiana researchers analyzed electroreceptor development in the embryos of the lesser spotted catshark, an animal that is largely motionless during the day and hunts at night, mainly in the seagrass beds of the eastern Atlantic Ocean.
Using molecular tests, scientists found two independent genetic markers of neural crest cells in the animal’s electricity-sensing organs. Analysis shows these cells migrate from the brain and travel into the developing shark’s head, creating the framework for the electrosensory system – a previously unknown function of a much-studied group of cells, according to Renata Freitas, a doctoral candidate in UF’s zoology department and first author of the paper.
The process mirrors the development of the lateral line that allows fish to mechanically sense their environment, and organs of the inner ear that enable people to keep their balance. But scientists suspect as human ancestors emerged from the sea, they discarded their lateral lines as well as their ability to sense electrical fields.
“Our fishy ancestors had the anatomy for it,” said James Albert, a former UF biologist who is now at the University of Louisiana. “You can imagine how valuable this system would be if you were aquatic, because water is so conductive. But it doesn’t work on land – air doesn’t conduct electricity as well. When it happens, it’s called a lightning bolt and you don’t need special receptors to sense it.”
All primitive animals with backbones could sense electricity, according to Michael Coates, an associate professor of organismal biology and anatomy at the University of Chicago. Mammals, reptiles and birds lost the sense over time, as did most fish alive today.
But in sharks and a few other species, such as sturgeons and lampreys, electrosensory capability endured.
“Most fish you see today have large eyes,” Coates said. “But sharks are predators that do not particularly rely on vision. If you see a hammerhead shark searching for flatfish, it moves its head back and forth, almost as if it were using a metal detector. Knowing that the electrosensory system may have developed with involvement of neural crest cells is valuable for people trying to reconstruct vertebrate evolution. It gives us further indication of how all of the various sensory systems come on line.”
But the idea that the neural crest truly is the source of the electrosensory system will raise eyebrows, scientists say.
“It’s a very interesting paper for two reasons,” said Glenn Northcutt, a distinguished professor of neuroscience at the University of California, San Diego, and a leading expert in vertebrate neurobiology. “For the first time, someone has shown which molecules may be responsible for guiding the development of the receptors of the lateral line system. I think this will hold true and is a very important finding. But I’m skeptical about the claim the neural crest gives rise to electroreceptors. It still requires a definitive experiment, where the developing neural crest cells are marked with dye, the embryo develops and the dye clearly shows up in the electroreceptors.”
Dye tests are a classical way of mapping cell movements during development, and have been used to explore the origins of limbs and brain cells. In the current research, scientists used genetic markers to trace neural crest cells.
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