Species Spotlight

PJ on wall- photo taken by Taronga Zoo.jpg

Port Jackson shark

Heterodontus portusjacksoni

What's in a name?

The Port Jackson shark (Heterodontus portusjacksoni) received its name after Port Jackson in Sydney, Australia, where it is commonly seen.

Their scientific genus Heterodontus is from the Greek word heteros meaning 'different' and dont meaning 'teeth'. This is because the teeth at the back are very different to those at the front, as you can see in the image below of a Port Jackson shark’s jaw.

Port_Jackson_Shark_Jaw_1.jpg

Anatomy and appearance

Port Jackson sharks, or PJs, are a medium shark endemic to Australia. They grow to about 1.65 m in length, with the boys being smaller generally. Their head is broad, blunts and flat, with prominent crests above their eyes.

PJs are not to be confused with their cousins, the crested horn shark () though, which are found in the same waters. Crested horn sharks are smaller and have much more angular crests above their eyes.

PJs, and crested horn sharks for that matter, have distinct ‘camo’ colouring of a mix of browns and beige. A defining characteristic of Port Jackson sharks though is the pattern of these markings. On their sides, above their pectoral fins and just in front of their first dorsal fin they have a dark brown triangle. Crested horn sharks don’t have this.

PJs are part of a group called ‘horn sharks’. These sharks have horns in front of both of their dorsal fins. The purpose of these horns is unclear, but when they hatch from eggs these horns are razor sharp and may provide a line of defence for the babies. Over time they are worn down from moving in and out of cramped caves where they like to sleep during the day.

 

Habitat

PJs are benthic sharks, meaning they spend a lot of their time resting on the sand or in caves and crevices. Unlike most sharks that must continually swim to breathe (ram ventilation, like great whites), PJs can site motionless on the sea floor and still breathe. They do this by something called ‘buccal pumping’. They can actively pump water over their gills my opening and closing their mouths.

PJs live on rocky, kelpy reefs with lots of caves and crevices. They are nocturnal, so you will often find them resting in these caves or on the sand if you come across them during the day. At night they are a whole other beast though and you’ll often seem them cruising around, quite quickly on the look out for a feed or a mate.

FIN FACT: Port Jackson sharks make HUGE annual migrations, of 1000s of kilometers, between breeding and feeding sites. In winter every year, adult PJs on the eastern coast of NSW will arrive to breeding sites in Jervis Bay and Port Stephens. After breeding they them migrate as far as northern Tasmania before doing it all over again the next year. Quite a feat for a little benthic shark!

Diet

We don’t know much about the diet of PJs but it is thought they feed on benthic shellfish, urchins and small bony fishes. Sherrie Chambers of the Fish Lab at Macquarie University is currently doing some really cool work using stable isotope analysis to figure out what they are eating during their breeding season and their annual migrations.

Reproduction

PJs are oviparous, meaning they lay eggs. During the breeding season, females will continually produce eggs, laying a new egg every 10 to 14 days. The eggs take about 10 months to develop into a baby shark, known as a neonate.

FIN FACT: Their rock reef habitats aren’t just good for hiding themselves, but also their eggs! Females will position themselves above cracks in the rocks and lay their eggs. The characteristic corkscrew design of the eggs means they fall into the crack and gentle waves help them to screw in further and stay in place.

Port Jackson shark egg. Image credit  Catarina Vila Pouca .

Port Jackson shark egg. Image credit Catarina Vila Pouca.

Conservation

Pjs are very common and considered ‘least concern’ on the IUCN red list of threatened species. It is estimated that their eggs suffer an over 80% mortality rate, with a major cause being other animals preying on the eggs. Crested horn sharks have been documented doing this quite often (see below).

Port Jackson sharks are also often caught by fishermen. If the hook is removed and they are returned to the water quickly they tend to survive well.

A crest horn feasting on a Port Jackson shark egg. Image credit: John Turnbull.

A crest horn feasting on a Port Jackson shark egg. Image credit: John Turnbull.

Meet the locals

Port Jackson sharks are very common on the eastern coast of Australia. In winter, during their breeding season, you are likely to see them in embayments such as Nelson Bay and Jervis Bay. In summer they are very common in embayments in Victoria, South Australia and northern Tasmania. Back further north, you’re likely to see eggs washing up from late spring when the babies start to hatch!

PJs are also found in in southern to central Western Australia.

Port Jackson sharks pose no threat to humans so have no fear if you come across one. If you were to grab one there is the risk they might bite; however, we don’t condone touching wild animals in any way. Like all animals, they are best enjoyed behaving naturally in their natural environment.

Diver cruising with a Port Jackson shark. Image credit: The Fish Lab, Macquarie University,

Diver cruising with a Port Jackson shark. Image credit: The Fish Lab, Macquarie University,

 

Written by Joni Pini-Fitzsimmons

Marine scientist and origami enthusiast

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Joni Pini-Fitzsimmons