22. Jan, 2022

The strange Port Jackson shark.

The Port Jackson  (PJ) shark  (Heterodontus portusjacksoni) belongs to the family of Bullhead sharks (Heterodontidae; derived from the Greek heteros odontis meaning different teeth) not to be confused with the Bull sharks (Carcharhinus leucas).

Left: two PJ sharks relaxing in a bed of sea-weed (picture by Paolo Bottari)

It can grow to 1.65 meters (5.5 ft) long, is oviparous in nature with its spiral-formed egg cases attached to seaweed, and is found in the depths of the Pacific Ocean in Australia. It is one of the three Australian species, along with the Crested Bullhead (H.galeatus) and Zebra Bullhead (H.Zebra). Another well-known species from the same family is the Horn shark  (H. francisci)  which is endemic along the southern part of the W-coast of the US. Compared with the elegant streamlined head and body of the more common Carcharhinus reef sharks, the PJ indeed is a strange-looking creature, raising the question of how evolution has produced this species. Probably its ancestry goes much further back than that of the more common sharks.

PJ  has a large, blunt head with prominent supraorbital ridges, probably also meant to protect the large eyes that lack a nictitating membrane.  It mostly has a dark to light brown skin, but individuals can vary in color between fawn, light brown, grayish-white, or even completely white (see insert). It has two dorsal fins, each preceded by a stout spine.

Typically, PJ shows harness-shaped stripe markings that cross the eyes, run along the back to the first dorsal fin, then cross the side of the body.  The shark has cone-shaped teeth in the front of a ‘pursed’ mouth flanked by oro-nasal grooves, with thick, grinding molars in the back of the mouths,  perfect for crushing hard-shelled mollusks, even including oyster shells.

 PJ is a migratory species, traveling south in the summer and returning north to breed in the winter. Both male and female species have a strong site fidelity. Adults are often seen resting in groups in caves, or on a sandy bottom (resembling nurse sharks). Like the horn shark, it is a sporadic swimmer that prefers to use its flexible, muscular pectoral fins to push itself along the bottom. The shark is not considered as threatened. Populations appear to be healthy, despite fishing activities.