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Victoria: A Shark on the Critical List - The Grey Nurse Shark (Carcharias taurus)
Mark Rodrigue, MESA Victoria

Slow to Breed

Grey Nurse Sharks are very slow to breed and can only produce a maximum of two pups each year which makes them particularly vulnerable to overfishing. When fish are removed from the environment at a faster rate than they can breed it is inevitable that the species will decline.

The Grey Nurse Shark grows slowly and takes 4 - 6 years to mature with both males and females maturing at about 220cm total length. Many scientists believe that Grey Nurse Sharks come together at certain times of the year in large groups at specific locations which is when mating occurs. The precise timing of mating and pupping in Australian waters is unknown.

Once she has mated the female Grey Nurse Shark stores the sperm inside her body while the ovaries produce eggs that move to the oviduct where they are fertilised. Not all migrating females are sexually active and they generally only reproduce once every two years.

Inside the mothers body the baby Grey Nurse Shark hatch from eggs inside the uterus with only one baby shark fully developing in each uterus. One challenge for the species is that they breed very slowly with only a maximum of two babies being born at any time. Baby Grey Nurse Sharks that are fully formed and independent of their mothers are born between 9 and 12 months after mating.

Grey Nurse Shark Cool Facts

What’s with the name - Grey Nurse Shark?

The grey part is easy – they are a grey /brown colour on top, although underneath they are white. This counter shading is a common feature of marine animals making them harder to see from above or below when swimming. The nurse part is believed to be due the ability of these sharks to “nurse” or round up schools of fish into compact schools before feeding on them.

What about their scientific name, Carcharias taurus, what is with that?

The genus names of Carcharias is shared amongst many sharks that have large pointed teeth including the Great White and Tiger Sharks. The word carcharo is a Greek word that means sharp pointed, jagged and refers to their teeth. Tauris is a Latin word that means bull refering to their stocky bodies.

Threats to the Grey Nurse Shark

The slow rate of breeding for the Grey Nurse Shark means that it is highly vulnerable to other threats. While Grey Nurse Shark numbers in Victoria and along the east coast have been severely depleted over the last 100 years there are a number of threats that continue to have effects on the recovery rate of the species even though they are protected by law. Protection under threatened species legislation makes it illegal in Australian waters to deliberately take Grey Nurse Sharks.

1. Fishing Impacts: Perhaps the greatest threat to recovery of Grey Nurse Shark populations is animals being killed as “by-catch” when they are caught accidentally in fishing activities that are targeting other species of fish. This occurs both in recreational as well as commercial fishing activity.

Grey Nurse Sharks are however “hooked” accidentally by recreational fishers seeking other species. This is a significant cause of the large numbers of sharks that are seen with wire traces and lures attached to their mouths and bodies. (Link to images of Grey Nurse Shark with lures).

Some sharks are also caught accidentally by commercial fishers as by catch (non-target fish caught in the net). In a few cases Grey Nurse Sharks caught this way have had their fins removed in a practice known as shark finning, an activity that results in many shark species around the world having their fins removed while still alive. The high value of shark fins leads to levels of catch of sharks worldwide that is unsustainable.

The fisher who caught this young Grey Nurse
shark released it straight afterwards.
(courtesy of Lance2004 via Flickr)

2. Beach Protection: A number of Grey Nurse Shark have also been caught up in shark nets designed to protect beaches from large predators. These nets that are set off swimming beaches trap many different kinds of animals with a number of Grey Nurse Shark being caught up in these nets. In recent years the number of sharks caught in this way has dropped dramatically as the overall number of sharks has declined.

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A Bad Reputation ....... But Not Deserved!
Slow to Breed
Threats to the Grey Nurse Shark
A Sixth Sense!
Baby cannibals!
Where can you see them?
What can we do to protect the Grey Nurse Shark from becoming extinct?
Going Further: Grey Nurse Shark Exploration activities
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