Port Jackson Shark: the shark that lays ‘corkscrew’ eggs

The Port Jackson Shark (Heterodontus portusjacksoni) is a nocturnal, bottom-dwelling shark that grows up to about 1.6 metres. It is commonly found in the temperate waters on the eastern, western and southern coast of Australia, usually at depths of less than 100 metres. It is named after the natural habour of Sydney where it is found.

Ridges on its head and harness-like markings

Horn Shark

Belonging to the family of Bullhead Sharks (Heterodontidae), the Port Jackson Shark has a large, blunt head with prominent arched ridges on its forehead. Its dark brown harness-like marking crosses the eyes, runs along the back to the first dorsal fin, and then crosses the side of its medium grey-brown body.

Eats and breathes at the same time

Most species of sharks need to swim with their mouths open to force water over their gills so as to absorb oxygen from the water. This is called ‘ram ventilation’. But Port Jackson Sharks can pump water into its first enlarged gill slit and out through the other four gill slits. With this method of breathing called ‘buccal pumping’, they need not swim continuously. Hence they can lie on the bottom for long periods of time, as well as eat and breathe at the same time.

Two types of teeth

Port Jackson Sharks hunt for hard-shelled mollusks, crustaceans, sea urchins, and fish.

In order to crush these stubborn shells, they are endowed with two types of teeth – small, pointed anterior teeth for grabbing prey, and large, broad, flat molar-like posterior teeth for crushing and grinding. Hence their scientific name heterodontus which means “different teeth”.

Port Jackson Shark
Image source: Wikipedia

Spiral shaped eggs

The oviparous Port Jackson Sharks are known for their unique spiral-shaped egg cases. Every year between July and August, large numbers of males and females gather to mate at the inshore reef areas of New South Wales in Australia, often congregating in caves and under rocky ledges.

Port Jackson Shark
Image credit: Australian Museum

Two weeks after mating, the female will lay about a dozen dark brown, spiral-shaped egg cases, each about 7 centimetres by 15 centimetres in size. She then uses her mouth to wedge the soft egg cases into rock crevices. The corkscrew design of the egg cases makes them difficult to dislodge, so they can harden and be kept safe from predators like the Crested Horn Shark. After which, she leaves.

10 to 12 months later, a single pup about 25 centimetres long emerges from each egg. Empty egg cases are often found washed-up on beaches, and are sometimes called “mermaids purses”.

The Port Jackson Shark can be found at the Seagrass Habitat, together with the Polka-dot Batfish and Dwarf Whiprays. Check them out the next time you’re at S.E.A. Aquarium!

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