Student Stuff

Greynurse Shark
Carcharias taurus Rafinesque, 1810

A Greynurse Shark at a depth of 17 m, off Sydney, New South Wales, February 2001. Photo © E. Schlögl. View larger image.

An albino Greynurse Shark at a depth of 18 m, Fish Rock, South West Rocks, New South Wales, August 2006. The fish on the back of the shark is a Slender Suckerfish.Photo © J. Cragg. View larger image. View movies of this fish.

Common name

The Greynurse Shark may take its common name from its ability to "nurse" (round up) small fishes into a tight school, for feeding. Of course it is also likely that it was named after the many other species of nurse sharks that occur worldwide, because of a superficial resemblance.

Scientific name

Carcharias taurus
carcharo - sharp pointed, jagged (Greek). Refers to the teeth.
taurus - bull (Latin). Presumably refers to the stocky body.

Family name

Odontaspidae
odonto, odon - tooth (Greek)
idae - suffix meaning that this a family name. All animal family names end in -idae.

Size

The Greynurse Shark grows to a length of 3.6 m. Males mature at 2.1 m and females at 2.2 m.

Number of species

There are over 370 species of sharks world wide, 166 occur in Australian waters. The family Odontaspidae contains two genera; Carcharias and Odontaspis. Two species (both genera) occur in Australian waters; the Greynurse Shark and Sandtiger Shark Odontaspis ferox.

Distribution

The family Odontaspidae is recorded throughout the world oceans. Greynurse Sharks are found in tropical and temperate waters in the Atlantic, Indian and western Pacific Oceans, although the species is known by different common names in different regions. It is recorded from all states of Australia except Tasmania.

Habitat requirements

The Greynurse Shark lives in shallow coastal waters from the surf zone down to 60 m, although it has been recorded from water as deep as 190 m.

During the day, they are generally found in the vicinity of dropoffs, caves and ledges. The image on the right shows typical Greynurse Shark habitat on the coastline of southern Sydney, New South Wales (view larger image).

Structural, physiological and behavioural adaptations

The Greynurse is a distinctive fish which is usually grey-brown on top and a dirty white underneath. A distinctive character of this species is that both dorsal fins and the anal fin are of a similar size. It is a sluggish species which is not considered dangerous to people, although divers should never provoke it.

View a low resolution movie clip (46k) of this species. Go to the movies page for high and low resolution versions.

Heterocercal Tail

Many sharks have a tail with a long upper lobe and a shorter lower lobe. This type of tail is described as heterocercal.

When a shark swims the large upper lobe of the tail tends to push the snout of the shark down. This is balanced by the lift produced by the pectoral fins and the ventral surface of the snout.

The tail of the Greynurse Shark is heterocercal and has a characteristic subterminal notch. This can be seen in the image above.

The lower image shows the tail of a Sandtiger Shark, the other odontaspid shark found in Australian waters.

More information on the Sandtiger Shark.

Electroreception

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 Greynurse Shark's snout is dotted with pores. Each of these leads to an organ (ampula of Lorenzini) which can detect electricity.

The underside of a Sandtiger Shark's snout. Arrows point to pores.

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.

Some sharks, such as the Great White, Carcharodon carcharias roll their eyes back in the sockets immediately before attacking prey. At this time, the electrosensory ability is most important because the shark cannot rely on sight.

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's) generates an electrical field through the conductor. Sharks can navigate by responding to changes in this electrical field.

Sharp Pointed Teeth

In some parts of the world, the Greynurse Shark is known as the Spotted Ragged-Tooth. The reason for the this name is obvious. This species has fang-like teeth which are visible when the shark's mouth is closed (view image). Greynurse Sharks are not however the "maneaters" that some people thought in the past.

The teeth of the Greynurse Shark are constantly being replaced. This means that older, damaged or blunt teeth on the exterior surfaces of the jaws are replaced by new teeth. In the whaler sharks, family Carcharhinidae, each tooth is replaced every eight to fifteen days.

They are sluggish sharks which feed on fishes, which are pierced with the sharp teeth.

Greynurse Shark jaws from the Australian Museum Fish Collection, registration number AMS IB.8145.View larger image.

Teeth of the Greynurse Shark. The front teeth are lanceolate (long) with a lateral cusplet (small barb) on each side (view a large image of a single tooth), whereas those at the back of the jaw are smaller and lack cusps.

Banded Wobbegong teeth are also long and slender.

A set of tiger shark jaws from the Australian Museum Fish Collection, registration number AMS I.27078-001.

The diet of the Greynurse Shark is very different to the "super-sharks" such as the Great White Carcharodon carcharias and the Tiger Shark Galeocerdo cuveri. These sharks have serrated blade-like teeth used for slicing meat off large prey such as marine mammals.

Large Oily Liver

Many bony fishes have a structure called a swim bladder which is used to control buoyancy. No shark has a swim bladder. Instead, sharks have different buoyancy regulating mechanisms that involve the liver and fins. The oily liver of the Greynurse Shark has been developed to a huge degree and occupies a large proportion of the body cavity. Shark oil is lighter than seawater and this gives the shark buoyancy. (View a large image of the liver of a White Shark, Carcharodon carcharias.)

One of the shark tanks in the Australian Museum Fish Collection. The discolouration of the alcohol preservative is partly due to shark oil.

The Greynurse Shark also swallows air at the surface, and holds it in the stomach. This provides buoyancy and enables the shark to hang almost motionless above the bottom.

In the early 1900s, shark liver oil was used to light the street lamps of Sydney.

The countershading of the Greynurse Shark.

Colouration

Greynurse Sharks are countershaded, the dorsal (upper) part is dark, mostly a grey to bronzy colour whereas the ventral (lower) part of the body is pale.

Juveniles have reddish or brownish spots on the posterior (back) half of the body and tail. These spots often fade as the shark ages, but are sometimes still visible on adults.

Many fishes that swim in open water are countershaded. This adaptation results in the fish being difficult to see from above because the dark colour of the dorsal surface of the fish blends into the dark colour of the water below. It helps to make the fish also less visible from below because the light colour of the underside of the fish is less noticeable against the light shining from above.

Reproduction

The Greynurse Sharks has an interesting twist to its reproduction, which begins, like all sharks with internal fertilization. The developing young are enclosed in egg cases within each uterus of the female. They hatch from the egg cases at about 55 mm in length and then eat not only unfertilised eggs, but also their brothers and sisters. After about nine to twelve months two young are born, one from each uterus. This is markedly different to the reproduction of the Port Jackson Shark.

The Greynurse Sharks is ovovivaparous, it produces eggs which hatch inside the female and have no placental connection. Other sharks such as the Port Jackson Shark lay eggs (oviparous sharks), or have a true placental attachment and give birth to live young (viviparous sharks), such as the Blue Shark, Prionace glauca. The Greynurse Shark is not the only shark in which the young are oophagous (egg eaters). Others include the Shortfin Mako Shark and Porbeagle Shark.

Follow-up questions

The Greynurse Shark has long pointed teeth ideal for piercing fishes. Name another shark which has similar teeth.
Greynurse Sharks are protected fauna in New South Wales. Why and when was this species protected?
How long is a Greynurse Shark pup when it is born?