the Legacy continues…………………….
Gregory R. Mann, Ph.D. {ret.}

Port Jackson Shark

“Heterodontus portusjacksoni”

The Port Jackson Shark has a blunt head and harness-like markings which cross the eyes, run along the back to the first dorsal fin, then cross the side of the body. This pattern makes it very easy to identify the species. They grow to 1.65 meters in length. More commonly, males grow to 75 centimeters and females between 80 to 95 centimeters. The Port Jackson Shark received its name after Port Jackson, Australia where it is commonly seen. The Port Jackson Shark occurs in southern Australian waters from southern Queensland south to Tasmania and west to the central coast of Western Australia. There are some questionable records of Port Jackson Sharks being caught as far north as York Sound in Western Australia. The species have been recorded only once from New Zealand. Studies of Port Jackson Shark genetics suggest there may be 2 populations in Australia, one occurring from southern Queensland to New South Wales and the second from north-eastern Victoria to Western Australia. Port Jackson Sharks usually live in rocky environments on or near the bottom. Sometimes they are found in muddy and sandy areas or where sea grass occurs.

Dietary items include sea urchins, mollusks, crustaceans and fishes. Black Sea Urchins are often eaten. Port Jackson Sharks forage for food at night when their prey are most active.  They often use caves and rocky outcrops as protection during the day. When most people think of shark teeth, they think of large, sharp teeth like those in the film ‘Jaws’. Not all sharks have teeth like these. The teeth of the Port Jackson Shark are very different. They are not serrated and the front teeth have a very different shape to those found at the back of the jaws, hence the genus name Heterodontus (from the Greek heteros meaning ‘different’ and don’t ‘meaning’ tooth). The anterior teeth are small and pointed whereas the posterior teeth are broad and flat. The teeth function to hold and break, then crush and grind the shells of mollusks. Juvenile Port Jackson Sharks have more pointed teeth and feed on a higher proportion of soft-bodied prey than adults. They can feed by sucking in water and sand from the bottom, blowing the sand out of the gill slits, and retaining the food which is swallowed. They have the ability to eat and breathe at the same time. This ability is unusual for sharks, many of which need to swim with the mouth open to force water over the gills. The Port Jackson Shark can pump water into the first enlarged gill slit and out through the other four gill slits. By pumping water across the gills, the shark does not need to move to ‘breathe’. It can lie on the bottom for long periods of time, a behavior that is observed at breeding time.

When they hatch, juvenile Port Jackson Sharks called pups are about 25 centimeters long. The breeding season is usually late winter and into spring. Divers regularly observe sharks congregating in caves, under ledges and in gutters. Port Jackson Sharks are oviparous, which means that the female lays eggs. The egg case is a tough, dark brown spiral about 7 to 8 centimeters wide and 15 centimeters long. It is common to see them washed up on beaches. The egg case is soft when laid by the female. She uses her mouth to wedge the egg case into a rock crevice where it hardens and from which one young shark emerges after 10 to 12 months. The Horn Shark has a similar-looking egg case with the addition of long twisted tendrils on the bottom end. These are often attached to seaweed. Female Port Jackson Sharks mature at 11 to 14 years of age, whereas males only take around 8 to 10 years.

Sharks are oviparous like the Port Jackson Shark, viviparous (give birth to live young) such as the Blue Shark or oviparous (produce eggs which stay in the female and hatch inside the parent with no placental connection) such as the Grey Nurse Shark. Port Jackson Sharks are considered harmless to humans although the teeth, whilst not large or sharp can give a painful bite. The Port Jackson Shark has two similar-sized dorsal fins. Each fin has a spine at the leading edge, which is reputed to be venomous. The spines of juveniles can be quite sharp, but those of the adults are usually blunt. The spines are sometimes found washed up on beaches and have been mistaken for all sorts of things from bird beaks to goat horns.

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