Species

Shark facts

• Shark Numbers

  The high number of shark species along our coastline is an indication of how healthy our marine ecosystems truly are.

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  In the 1990’s concern about some shark stocks led to big reductions in commercial fishing of targeted species. Only a few commercial fisheries are now authorised to sell their shark and ray catches and they operate under strict controls.

  The white shark, whale shark, northern river shark, grey nurse shark and all sawfish (which are related to sharks) are also listed as protected species and can’t be kept by commercial or recreational fishers. There’s also a maximum size limit for all whaler shark species, including tiger sharks, in the West Coast and South Coast Bioregions. 

• Biology

  Sharks belong to a class of fish called Chondrichthyes, which have skeletons made of cartilage and not bone.

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  Sharks are typically slow growing, late maturing, long-lived and produce only a few young per year, which makes many species more vulnerable to overfishing than most bony fish.

  Sharks are covered in tough scales called dermal denticles, making their skin extremely tough and abrasive. Sharks have between five and seven external gills.

  Some sharks that live on the seabed, such as angel sharks and wobbegongs, have a flattened shape, like a ray. However, most sharks have a torpedo shaped body, large dorsal and pectoral fins to keep them stable and to help them steer, and a large tail or ‘caudal’ fin for propulsion. 

  Many sharks need to keep swimming in order to breathe, while others can pump water over their gills while they’re still or above the seabed. 

  Sharks have a continuous supply of teeth to replace damaged teeth. A shark can have up to 3,000 teeth in its mouth at one time and produce more than 30,000 teeth in its lifetime.

  Sharks’ teeth vary according to their diet. White sharks have large serrated teeth for cutting big prey, while grey nurse sharks have long, needle-like teeth, used for gripping prey. Port Jackson sharks and many ray species have large plate-like teeth for crushing hard-shelled prey, like crabs and other invertebrates. 

• Shark Senses

  Sharks have well-developed eyesight and sense of smell.

   

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  Like other fish, sharks have clusters of hair cells called ‘neuromasts’ in canals just below their skin along the sides of their bodies and around their head and mouth. These can sense vibrations in the water caused by fish movements for example.

  Sharks can also sense the weak electrical signals produced by most living organisms, through pores in their snouts and heads called ‘ampullae of Lorenzini’. These pores help them find prey buried in sand or hidden by darkness. It’s thought they might also help sharks navigate by responding to fluctuations in the Earth’s magnetic fields.

• Upper Level Predators

  Many people are scared of sharks, but some sharks might have more to fear from humans than we do from them. 

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  Their slow rate of reproduction means many species of sharks are highly vulnerable to fishing and may take a long time to recover if stocks are depleted. 

  As a group, sharks feed on a wide variety of prey, including fish, squid, octopus, crustaceans, mammals, reptiles and other marine creatures. The overwhelming majority of shark species feed almost entirely on a variety of fish and invertebrates. 

  Whale, basking and megamouth sharks filter feed on plankton and have relatively small teeth because they don’t need them to feed. Instead, these sharks have modified extensions on their gill arches that allow plankton to be sieved from the water as they swim, or when deliberately pumping water through these gill rakers. 

  Sharks are an important component of healthy aquatic ecosystems and play a part in regulating the size and ‘genetic fitness’ of prey populations. 

• Life Cycle

  Different species of sharks have lifespans varying from a few years to several decades.

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  One of the species that has been studied in the most detail in WA, the dusky shark, probably lives longer than 50 years and females don’t start reproducing until they’re 29 years old. 

  Not only are sharks generally slow to mature; some species don’t even reproduce every year. 

  Unlike bony fish, shark eggs are fertilised internally in females after sperm is delivered via one of the male’s two ‘claspers’ (elongated and rigid tubes of skin immediately behind its pelvic fins).

  Many shark species are viviparous, which means they give birth to live young. Embryos fully develop in the mothers’ two uteri and are born as well-formed miniature sharks. 

  In viviparous shark species, developing embryos either receive nutrition from a large yolk-sac or directly from the mother, either through uterine secretions or through a placenta, similar to mammals. 

  Other species deposit partially developed embryos in special leathery egg cases on the sea floor, a method called oviparity. Sometimes, particularly after storms, empty egg cases or “mermaid’s purses” wash up on shore.

• Distribution and Habitat

  Sharks live in every ocean on earth, most estuaries and even in some large freshwater rivers.

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  The greatest known diversity of sharks tends to be in continental shelf waters, although they also occur in the open oceans and in the depths below.

  Some species prefer particular types of habitat, such as coral reefs, sea grass beds or tidal mangrove forests, while others regularly wander between many habitat types, or even between the tropics and cool temperate zones.