Fast Facts: Grey Nurse Sharks

  • The Grey Nurse Shark is listed as two separate populations within Australia. The east coast population is listed as critically endangered. The west coast population is listed as vulnerable.
  • This species became the first protected shark in the world when the New South Wales Government declared it a protected species in 1984.
  • The Grey Nurse Shark is also known as the sand tiger shark or spotted ragged-tooth shark.
  • It has a large body and is coloured grey to grey-brown dorsally, with a paler off white under belly.
  • Reddish or brownish spots may occur on the caudal fin and posterior half of the body, particularly in juveniles.
  • They have a conical snout, long awl-like teeth in both jaws, similarly sized first and second dorsal fin and an asymmetrical caudal fin.
  • Grey nurse sharks grow to at least 3.6 metres in length. The grey nurse shark is a slow but strong swimmer and is generally more active at night.
  • They are often observed just above the sea bed in or near deep sandy-bottomed gutters or rocky caves, in the vicinity of inshore rocky reefs and islands.
  • Their diet consists of a wide range of fish, other sharks, squids, crabs and lobsters.
  • The teeth of the Greynurse Shark are constantly being replaced. Older, damaged or blunt teeth on the exterior surfaces of the jaws are replaced by new teeth.
  • Until recently, the grey nurse shark had an undeserved reputation in Australia as a man-eater. Harding (1990) found that it is not a threat to divers or swimmers unless provoked.
  • Many shark attacks in Australia have been attributed incorrectly to the grey nurse shark (Whitley, 1983) often due to its fierce appearance.
  • The grey nurse shark’s reputation led to indiscriminate killing of the species by spear and line fishers.
  • Current threats to the species are believed to be incidental catch from commercial fisheries, recreational fishing and, to a lesser extent, the bather protection programs run in New South Wales and Queensland.
  • The sharks are able to swallow air at the surface of the water in order to give them buoyancy control.
  • Sharks have the same five senses as humans; taste, touch, sight, hearing and smell, but in addition have a sixth sense; electroreception. The underside of the Grey Nurse Shark’s snout is dotted with pores. Each of these leads to an organ which can detect electricity.
  • Sharks can detect very weak electrical currents. This extra sense gives sharks the ability to detect and attack prey at close range without needing to see the prey item. This can be advantageous in murky water or if the shark is a bottom feeder which relies on finding prey buried in the sediment.
  • The electroreception capabilities of sharks also gives them the ability to navigate using the Earth’s magnetic field. This is possible because an electrical conductor (the shark) moving through a magnetic field (the Earth) generates an electrical field through the conductor. Sharks can navigate by responding to changes in this electrical field.
  • Internal fertilization occurs in all sharks. Sperm transfer occurs through the claspers of the male.
  • During the 9-12 month gestational period, the embryo sharks are held in egg cases inside the mother’s uterus. The unborn young eat the other eggs inside the egg case until only one is left.
  • At about 5.5 centimetres long, the young shark hatches from the egg case but is still held inside the uterus. When about 10 centimetres long it develops teeth and will hunt other embryos inside the uterus until there is only one survivor in each of the mother’s two uteruses. The mother eventually gives birth to two live pups.

“The low reproductive rate of only two live pups in each birth, further hinders the success of this species – Karina Teuma, Year 2021.

References: environment.gov.au; Environment Protection and Biodiversity Conservation Act 1999; dpaw.wa.gov.au; australian.museum; End Quote by Karina Teuma.

Published by Karina Teuma

karinateuma.com Karina Teuma is a Passionate Marine Biology Enthusiast, Environmentalist, Snorkeller, Freediver, Scuba Diver and more.

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