Port Jackson or Dog Shark (Egg)

Description:

Description: The Port Jackson Sharks 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. Only the heterodontid sharks have the combination of no anal fin and spines on the leading edge of the two dorsal fins. The family Heterodontidae has eight species, all in the genus Heterodontus, three of which are found in Australian waters. These are the Port Jackson Shark, the Zebra Horn Shark, Heterodontus zebra, and the Crested Horn Shark, Heterodontus galeatus. Size range: The Port Jackson Shark grows to 1.65 m in length. More commonly, males grow to 75 cm and females between 80 cm and 95 cm.

Habitat:

Habitat and Distribution: Port Jackson Sharks usually live in rocky environments on, or near, the bottom. Sometimes they are found in muddy and sandy areas, or where seagrass occurs. These sharks occur in southern Australian waters from southern Queensland to Tasmania and west to the central coast of Western Australia.

Notes:

Found at the Grange jetty (South Australia) The size of this egg was about 13cm, there was an opening at the blunt end so thankfully there was no occupant :-) Feeding and Diet: Dietary items include sea urchins, molluscs, crustaceans and fishes. Black sea urchins, Centrostephanus rodgersi 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. The teeth of the Port Jackson Shark are very different to other sharks, as they are not serrated, and the front teeth have a very different shape to those found at the back of the jaw, hence the genus name Heterodontus (from the Greek heteros meaning 'different' and dont '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 molluscs and echinoderms. Mating and Reproduction: The breeding season is usually late winter and into spring. At this time, 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 cm to 8 cm wide and 15 cm 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 ten to twelve months. The Crested 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 ovovivaparous (produce eggs which stay in the female and hatch inside the parent with no placental connection), such as the Grey Nurse Shark. Other behaviours and adaptations: Port Jackson Sharks 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 behaviour that is observed at breeding time. Danger to Humans: Port Jackson Sharks are considered harmless to humans, although the teeth, whilst not large or sharp, can give a painful bite. The 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. These spines are believed to have given rise to the common name of the family, 'Horn Sharks'. My information came from: http://australianmuseum.net.au/Port-Jack...