Sharks in Australian waters

Whale shark

Whale shark Photo: Paradise Ink

Worldwide, there are about 400 species of sharks. Of these, around 180 species occur in Australian waters, of which about 70 are thought to be endemic. Sharks occur in all habitats around the Australian coast line, however most are found on the continental slope or shelf, primarily on the bottom. However, many sharks are also found in coastal waters and a small number are even found in freshwater systems, such as rivers and estuaries.

Legislative protection

Environment Protection and Biodiversity Conservation Act 1999

In Australia, most sharks can be legally caught by commercial and recreational fishers. However, due to declines in numbers, a handful of species are now listed as 'threatened' under the Environmental Protection and Biodiversity Conservation Act 1999.

Under the EPBC Act, it is an offence to kill, injure, take, trade, keep, or move any member of a listed threatened species on Australian Government land or in Commonwealth waters without a permit. The EPBC Act also requires that any action that has, will have or is likely to have a significant impact on a threatened species must be referred to the Department of the Environment for assessment before the action goes ahead.

The listed shark species are:

Critically endangered species

Endangered species

Vulnerable

Legislative changes for recreational fishing of three shark species

Memorandum of Understanding on the Conservation of Migratory Sharks

The Memorandum of Understanding on the Conservation of Migratory Sharks was developed under the auspices of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). Australia became the 14th country to sign the Sharks MoU, signing on 4 February 2011.

Six out of these seven species covered by the Sharks MOU occur in Australian waters - the white shark, whale shark, basking shark, porbeagle, shortfin mako and longfin mako.

Action under the Sharks MoU aims to improve understanding of migratory shark populations, key pressures and key habitats, and current and future actions to conserve these species.

Recovery plans

Under the threatened species legislation, listed threatened species can have a recovery plan made in order to guide actions to help the species recover.

Currently, recovery plans exist for the white shark, grey nurse shark and whale shark. Reviews of the white shark and grey nurse shark recovery plans have recently been completed. The reviews concluded that while progress had been made on many of the actions listed in the plans, there remained a need for a recovery plan for the species and that new plans should be made which removed completed actions and included new conservation priorities. New plans for both species are currently being drafted.

In addition to the existing plans, a multi-species recovery plan is currently being developed for the three species of sawfish and two Glyphis species.

Habitat and biology

Sharks are primarily oceanic and are widespread in tropical to temperate zones. Sharks vary greatly in size. The largest species, also the largest of all fishes, is the plankton eating giant the whale shark (Rhincodon typus). The largest measured specimen was 12.65 m long and weighed 21.5 tonnes, but the whale shark probably attains 18 metres. Some of the deepwater shark species attain only about 25cm.

Sharks (elasmobranchs) comprise about 1% of all living fishes, and share nearly all the major features of their finned relatives. Like all fishes sharks use gills to extract oxygen from the water in which they live. Sharks have five to seven gill openings along each side of the head, through which they breathe. Primarily marine fishes, a few have adapted to fresh water, such as the Northern River shark and speartooth shark (Glyphis garricki and Glyphis glyphis) found in northern Australia.

Feeding

Most sharks are predators. Many sharks species become active after dusk and hunt during the night. The majority of sharks feed on other fishes. Large sharks, such as the white shark (Carcharodon carcharias) and tiger shark (Galeocerdo cuvier), prey on large marine mammals such as seals, sea-lions, dolphins as well as large fishes, turtles and even sea birds.

While some sharks are probably not very selective feeders, certain sharks eat some foods more than others. For example, hammerhead sharks are known for eating stingrays; bull sharks eat other sharks; and smooth dogfish eat crabs and lobsters. Many species of sharks are adapted for bottom feeding. Bottom feeders use the upper jaw to help pick up prey items. One example of a bottom feeder, the Port Jackson shark (Heterodontus portusjacksoni), has two types of teeth. Front teeth are pointed for grasping and back teeth are flat and molarlike for crushing. Another mechanism some sharks use for collecting food is filter feeding. The basking shark (Cetorhinus maximus) and the megamouth shark (Megachasma pelagios) strain enormous quantities of plankton from the water on gill rakers. Whale sharks also filter feed, but instead of using gill rakers, they strain plankton through a spongy tissue supported by cartilaginous rods between the gill arches. Filter feeders have reduced, nonfunctional teeth.

Several species of shark are known to be dangerous to humans: the white shark, tiger shark, bull shark (Carcharhinus leucas) and other whaler sharks (Carcharhinus sp.). No shark is thought to target humans as prey, rather the majority of shark attacks can be attributed to the shark confusing us with its normal prey.

Breeding

Mating in sharks is facilitated by the clasper organs of males, which are inserted into the female's cloaca during courtship. Fertilisation is always internal, and reproduction occurs in one of three modes:

  1. Laying eggs (oviparous)
  2. Live bearing (viviparous)
  3. Young hatching from eggs within the mother (ovoviviparous)

Examples of all three reproduction methods are found in sharks living in Australian waters. The Port Jackson shark lays spiral shaped eggs that young hatch from (oviparous), the smooth hammerhead (Hphyrna zygaena) gives birth to live young (viviparous) and the grey nurse shark (Carcharias taurus) gives birth to pups after they have hatched from eggs within the uterus (ovoviviparous).

Threats

Sharks are relatively long lived, slow to reach sexual maturity and have low fecundity rates. This suite of characteristics makes many species of sharks vulnerable to mortality above natural levels, either through harvesting by commercial or recreational fishing or through depletion from other sources such as habitat degradation or shark control activities.

Shark attack

Many Australians are concerned about the risk of shark attack. However, fatal shark attacks occur relatively infrequently in Australian waters - over the last 50 years there have been 53 fatal attacks, which is approximately one fatal attack per year.

There are some easy and commonsense precautions to take that can help reduce the risk of a shark attack. This risk minimisation advice is reproduced from the Australian Shark Attack File.

  1. Swim at beaches that are patrolled by Surf Life Savers.
  2. Do not swim, dive or surf where dangerous sharks are known to congregate.
  3. Always swim, dive or surf with other people.
  4. Do not swim in dirty or turbid water.
  5. Avoid swimming well offshore, near deep channels, at river mouths or along drop-offs to deeper water.
  6. If schooling fish start to behave erratically or congregate in large numbers, leave the water.
  7. Do not swim with pets and domestic animals.
  8. Look carefully before jumping into the water from a boat or wharf.
  9. Do not swim a dusk or at night.
  10. Do not swim near people fishing or spear fishing.
  11. If a shark is sighted in the area leave the water as quickly and calmly as possible.

For more information on shark attacks, risk minimisation, statistics and maps, please see:

Resources

National action plan

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