Fish
Port Jackson Shark
Heterodontus portusjacksoni · also called port jackson shark, oyster crusher
The Port Jackson shark looks like it was designed by committee: a blunt, pig-like snout, heavy brows, a dark harness pattern across the body, and a sharp spine sticking up from each fin. It is a slow, harmless reef shark of southern Australia that crushes sea urchins for a living, and the female packs her young into spiral, screw-shaped egg cases jammed into the rocks.
Overview
Port Jackson sharks live on rocky reefs and seagrass beds around southern Australia. They are stocky and 1–1.6 m long, with ridges over the eyes, harness-like markings, and a spine at the front of each dorsal fin for defence. They eat sea urchins, molluscs, and crabs, gripping prey with pointed front teeth and grinding it with broad flat back teeth — the “different teeth” the genus name refers to.
Eating and breathing at once
It can pump water in through its first gill slits and out through the rest while food is held in its mouth, so it does not have to stop breathing to feed — something most sharks effectively must do.
Screw-shaped eggs
The female lays a tough, dark, auger-shaped egg case and uses her mouth to wedge it into a rock crevice, where the spiral jams it in place against predators. The pup hatches after 10–12 months.
Homing
Individuals migrate hundreds of kilometres but return to the same reef to breed year after year, navigating with a precision unusual for a bottom-dwelling shark.
Status
The Port Jackson shark is Least Concern, common and stable, docile, and harmless to people — by day it rests in caves and gutters, often in loose piles of several sharks.
Port Jackson Shark: common questions
Why does the Port Jackson shark have a spine on its fin?
Each of its two dorsal fins carries a stout, sharp spine along the leading edge, and these are defensive. A predator such as a larger shark that tries to swallow a Port Jackson shark gets a mouthful of spines, which can wedge the prey open or simply make it too painful to hold, and there are records of bigger sharks found dead with a Port Jackson shark stuck in the throat. The spines also make the shark awkward to handle for anglers who catch one. They are a feature of the whole horn shark family, all of which are slow, bottom-living sharks that rely on armour and crushing jaws rather than speed.
What are those spiral egg cases washed up on Australian beaches?
They are very likely Port Jackson shark eggs. The female produces a dark brown, leathery capsule shaped like a large screw or corkscrew, roughly the size of a hand, with two spiral flanges running along it. Right after laying it she takes it in her mouth and works it into a rock crevice, where the spiral shape jams it firmly in place and stops fish and octopuses from pulling it out while the embryo develops over the following year. Empty cases that have come loose after hatching often end up in the strandline, where beachcombers find them.
Is the Port Jackson shark dangerous?
No. It is a small, slow, placid shark with a diet of urchins and shellfish and a mouth built for crushing, not biting large prey. It shows no interest in people, and divers on southern Australian reefs regularly swim among resting groups of them without incident. The only real hazards are the fin spines if you pick one up, and a firm crushing bite if you deliberately put a finger near its mouth, neither of which is a danger to anyone leaving the animal alone.
How does a bottom-dwelling shark navigate hundreds of kilometres back to the same reef?
The details are still being worked out, but tracking studies show that Port Jackson sharks in New South Wales move south along the coast after breeding and return north to the same reef, sometimes the same ledge, in later years. Sharks in general have a well-developed magnetic sense and can detect tiny electric fields and probably use smell and water chemistry, and the Port Jackson shark is thought to combine these cues into a reliable homing ability. The behaviour matters for conservation, because a local reef population that is wiped out may not be quickly replaced by sharks from elsewhere.