Species Spotlight

shark-506025_1920.jpg

Grey nurse shark

Carcharias taurus

What's in a name?

The grey nurse shark (Carcharias taurus) is also known as the sand tiger shark, spotted ragged-tooth shark and blue-nurse sand tiger. They're also commonly called the Labradors of the sea due to their placid nature and the fact that there has been no reported attacks of humans from this species.

Their scientific name, Carcharias taurus, is latin and roughly translates to "bull shark". Their closest relative, however, is actually the great white shark (Carcharodon carcharias). They are a shark in the oder Lamniformes, which comes from the greek "Lamna", meaning "fish of prey". This order of sharks are known as mackerel sharks, and includes some of the most well-known shark species, including the great white and the extinct megalodon, as well as some of the more unusual shark species, including the goblin shark and the megamouth shark.

Anatomy and appearance

Grey nurse sharks grow up to about 3.2m total length and can weigh up to 160kg. They have a pointy head but a relatively stout and bulky body. They are white on the underside and grey on the dorsal side, with dark spots on their flanks, which are like big freckles. These spots are used to identify individuals for conservation projects like Spot A Shark.

Spot A Shark  was developed to monitor the Australian grey nurse shark population and record changes at their local aggregations sites.

Spot A Shark was developed to monitor the Australian grey nurse shark population and record changes at their local aggregations sites.

FIN FACT: Grey nurse sharks are actually able to swallow air at the surface of the water as a means of controlling their buoyancy. Unlike fish, sharks don't have gas-filled swim bladders to control their position in the water column. Sharks rely on their huge, oily livers to help with buoyancy. The oil is lighter than water, but the sharks body as a whole is not. This is why sharks have to continuously swim to keep off the bottom. The grey nurse sharks unique ability to swallow air to keep them neutrally buoyant helps reduce the effort needed to stay off the bottom!

Habitat

As you can see in the picture below, grey nurse sharks are a sub-tropical to temperate species with a broad global distribution. They are a relatively shallow water species, being found at depths up to 290 metres. They're found on the continental shelf on submerged reefs and sandy bottoms, as well as within estuaries and embayments.

Grey nurse sharks are found in temperate and sub-tropical coastal waters all over the world.

Grey nurse sharks are found in temperate and sub-tropical coastal waters all over the world.

Diet

Seemingly docile during the day, grey nurse sharks are actually stealthy hunters at night, feeding on fishes, crustaceans, cephalopods and even smaller sharks. They can travel far to hunt at night and are known to hunt in relatively deep waters, returning to shallow caves and crevices for shelter during the day.

Reproduction

In Australia and South Africa, grey nurse sharks make annual migrations which can be over 3,000km. In the late winter to late spring, they pup in relatively cold waters of about 16°C in the southern and central parts of their range. They then migrate north and mate during late spring to early winter. In late summer to early winter, they travel further north to warmer waters for gestation. They then make the return trip to the southern parts of their range to pup again.

Shark mating is often confronting and erratic. Males grey nurse sharks bite onto the sides and fins of the female, often leaving her with bad cuts and scrapes. For grey nurse sharks, mating usually takes place at night. Like last months Species Spotlight - smooth stingrays - grey nurse sharks are ovoviviparous, meaning baby sharks will hatch from the egg within the uterus before being born.

Grey nurse sharks are about 1m at birth. Males reach sexual maturity at 5 to 7 years of age. Females don't reach sexual maturity until about 7 to 10 years of age.

FIN FACT: When a baby grey nurse shark hatches from its egg within the uterus, it will then feed on any other embryos and eggs until they are big and strong enough to face the outside world. This is called "intrauterine cannibalism", "embryophagy" or "adelphophagy". The latter literally means "to eat one's brother"!

Grey nurse sharks reproduce at a very low rate. Due to intrauterine cannibalism, they only give birth to 1 to 2 pups per litter. They also only breed every 2 or 3 years.

Conservation

Grey nurse sharks have been in severe decline across their range since the 1980's. This species faces a number of threats - they are/have been:

  • targeted by spear fishers in 1950s - 60s

  • a highly priced food item in the western northern Pacific ocean

  • a popular trade item in Japan

  • fished for their hide and fins off North America

  • fished for shark liver oil, which is used in cosmetics (aka "squalene")

  • fished for fishing competitions in South Africa and other countries

  • poisoned by spear fishers in Australia

  • a popular aquarium exhibit in the USA , Europe, Australia and South Africa because they are so docile and adapt well to captivity

  • caught in shark nets

  • accidentally caught on hooks and lines used recreationally

  • pups are harmed by pollutants in estuaries in the USA

Due to their very low reproduction rate their recovery from threats is severely hindered.

This species is now listed as:

GNS dive spots.png

Meet the locals

In NSW, we are super lucky to have a number of places where you can dive with aggregating grey nurse sharks right our doorstep. Here are a couple of our favourites:

  • South Solitary Islands off Coffs Harbour

  • Fish Rock, South West Rocks

  • Seal Rocks near Forster

  • Broughton Island off Port Stephens

  • Magic Point off Maroubra in Sydney.

For a great overview of these sites, check out Diveplanit.

Diving with grey nurse sharks

It is always recommended to dive with a reputable dive centre. Prior to your dive, you should be briefed on how to behave and interact with the sharks you may encounter.

Due to their threatened status, in NSW diver must comply with the Code of Conduct for Diving With Grey Nurse Sharks. This Code was developed as part of the Recovery Plan for the Grey Nurse Shark (Carcharias Taurus) in Australia.

Simply put, when encountering grey nurse sharks, divers aren't allowed to:

  • touch, feed or interfere with natural behaviours of the sharks;

  • chase, harass or interrupt the swimming patterns of the sharks;

  • get in the way of sharks entering or exiting caves and crevices;

  • dive in groups of 10 or more divers;

  • dive at night at sites considered critical habitats; or

  • use mechanical apparatus such as scooters.

The best experiences are when you simply sit and watch the sharks from one spot to the side of the aggregation. This lets you see them moving naturally in their environments and with other sharks.

Written by Joni Pini-Fitzsimmons

Marine scientist and origami enthusiast

Twitter | Instagram | Facebook

Joni Pini-Fitzsimmons