Shark diversity in Australia is one of the richest in the world. Australia’s waters are home to over 170 species of shark, of which 70 are thought to be found nowhere else.
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We are host to the world’s largest, whale shark, which can grow to around 12m in length, as well as to the one of the smallest, the pygmy shark, which measures no more than around 25 cm in length.
Worldwide, sharks have seen a decline in population numbers with many threatened with extinction according to the ICUN Red List. Australia is also witnessing the same trend with several species on the threatened list and is considered a hotspot when it comes to shark depletion.
The ICUN Red List indicates that the Grey Nurse shark, the Great White shark and Scalloped Hammerhead, all found in Australian waters include some of the threatened species. Australia’s oceans are also home to the three most deadly sharks responsible for almost all recorded shark attacks in Australia, namely the Great Whites, Tiger Sharks and Bull Sharks. That being said, despite the omnipresent fear of shark bite, 97% of all shark species are harmless.
The Grey Nurse Shark is also known as the sand tiger shark or spotted ragged-tooth shark. Australia is home to two populations of the Grey Nurse Shark, the west coast population located in the southwest coastal waters of Western Australia and the east coast population located along the coast of New South Wales and Southern Queensland.
The Grey Nurse Shark on the east coast of Australia and has been protected under Australian Law since 1984, being the first protected shark species in the world. It remains classified as Critically Endangered. They have the lowest reproductive rate of any shark, which does not help their declining numbers, producing just two pups per litter and only once every two years. The Grey Nurse is able to swallow air at the surface of the water which provides them with buoyancy control and so prefer shallow waters close to inshore rocky reefs and islands. They are known for their placid nature and do not pose a threat to divers and swimmers. They are also more active at night.
These sharks occur more frequently during the warmer months and at higher altitudes. They can be located around Northern Australia, as far down as Sydney, NSW and Geographe Bay WA. Being light-sensitive they primarily inhabit shorelines during the day and deeper waters at night.
They are considered safe for swimmers and divers, not known to be aggressive toward humans. In fact, they are known for their social behaviour – swimming in packs of 100 or more when they decide to get together. Their reproduction rate is high compared to other species, producing 15 to 30 pups per litter.
Great Whites are legally protected as Vulnerable in Australia.
Great Whites can grow about 250 mm in length every year.
They are found from southern Queensland to the North West Cape in WA. The population of Great Whites on the east coast alone is estimated to be around 5,460. The largest flesh-eating shark in the world, it favours shallow, temperate seas and normally dines on fish and marine mammals, such as seals.
The liver is equal to a quarter of the body weight in some sharks. In the case of the Great White, its liver is 28% of the entire body weight (28% of 2,000kg in the case of the biggest known Great White, ‘Deep Blue’). Sharks can lose their teeth and grow replacements, to the point where they can have around 20,000 teeth over a lifetime. Great Whites have 5 rows of teeth and 300 teeth at any one time. Reproducing once every 2 to 3 years, with between 2 and 10 pups per litter, Great Whites mature at 12-18 years for females and 8-10 years for males. They can grow to 6.4 metres in length. An apex predator, the Great White is protected internationally after its numbers fell into decline due to interactions with commercial and recreational fisheries and shark control programs.
Tiger Sharks are found in Australia’s northern waters from NSW to Perth WA. In terms of size, only Whale Sharks, Basking Sharks, and Great Whites get bigger.
Tiger Sharks are declining in number. They’re not protected and the Tiger Shark population has dropped by more than 70% over the past 30 years. Female Tiger Shark pregnancies last for 14 to 16 months. They give birth to an average of 30 pups, with as many as 80 being reported. The species is under threat because many Tiger Sharks are killed by fishing practices targeting other species, as well as by illegal fin harvesting. In Australia, tiger sharks are baited and culled in areas where shark attacks are a concern.
Tiger Sharks will eat anything from an albatross to venomous sea snakes to other sharks, even rubber tyres and paint cans. Their notched teeth can shear through the thickest of hides and are angled so prey struggling to escape only manage to inflict further injury on themselves.
Bull Sharks can move seamlessly between freshwater and saltwater environments, posing a serious threat in coastal rivers, harbours and lakes. Bull sharks traverse freshwater as well as saltwater thanks to an ability to regulate the concentration of salt in their blood. This makes it difficult to estimate their numbers.
Estimates say there are more than 500 bull sharks just in the Brisbane River.
Bull Sharks are known for being aggressive, however, their curious and reactive nature can lead to an investigatory bite. But catastrophic damage often results, due to razor-sharp teeth and a bite, pound for pound, more powerful than the Great White’s.
Bull Sharks give birth to 1-13 young per litter. The species is under threat because of human impact, directly as well as on their habitat.
The Shortfin Mako (Isurus oxyrinchus) is the fastest shark, reaching 40 kph at a regular swimming speed and nearly 75 kph in short bursts that allow it to fly through the air. To help with propulsion in the water, a shark can stiffen its tail as it swings back and forth. In addition, sharks’ skin is made of millions of small v-shaped scales, called dermal denticles, that decrease drag in the water. A shark's skeleton is cartilage, not bone, and lightweight. This means further swimming efficiency. Bull Sharks can reach speeds of 40 kph. Tiger Sharks top out around 32 kph. Great Whites, with a cruising speed that matches the fastest Olympic swimmer, can get up to 56 kph.