Port Jackson Shark

Encountering Port Jackson sharks is a classic experience for divers exploring the temperate reefs of southern Australia. During daylight hours, these sharks are sluggish and spend their time resting on sandy cave floors, wedged beneath rocky ledges, or gathered in shallow, sheltered gutters. Divers often find multiple individuals resting together, as preferred sites can host up to 16 sharks at a time while nearby identical crevices remain empty.

Approach resting sharks slowly and neutrally buoyant to avoid stirring up bottom sediment. Although Port Jackson sharks are calm and harmless to humans, divers should maintain a polite distance and avoid touching or grabbing them. Handle them with extreme care if encountered closely: their leading dorsal fin spines are venomous and can inflict painful wounds, while their small anterior teeth are sharp enough to bite if the animal is provoked.

Divers interested in reproductive behaviour should look closely inside rocky crevices and narrow fissures during late winter and spring. Here, female sharks can sometimes be seen actively carrying soft, spiral-flanged egg cases in their mouths, carefully wedging them deep into rock gaps where they harden over time to prevent predation and detachment by surge.

The optimal time to dive with Port Jackson sharks varies by region and matches their annual reproductive and migratory cycles. The peak period for coastal encounters along New South Wales and eastern Australia occurs during late winter and spring, primarily from late July through October.

In late July and August, mature male sharks move into shallow coastal embayments, harbours, and reefs, followed shortly by adult females. During August and September, mating occurs, and females lay their spiral egg cases in shallow rocky crevices, typically at depths between 1 and 5 metres, though sometimes down to 30 metres. During this breeding window, large aggregations form in gutters and caves across locations such as Sydney, Port Stephens, and Cabbage Tree Bay.

By late September or October, adult sharks begin leaving the shallow breeding grounds. Males depart first, followed by females, embarking on a southward migration to summer feeding grounds in areas like the Bass Strait. Tagging studies show females may travel 600 to 850 kilometres south, with some ranging as far as Tasmania, before returning to the same breeding reefs the following winter. Consequently, coastal shallow-water numbers drop significantly during the summer months.

The Port Jackson shark is endemic to the temperate and subtropical continental shelf waters of southern Australia. Its geographic range extends from Byron Bay (and potentially southern Queensland) along the eastern coast, down around Tasmania, and west to the Houtman Abrolhos off the central coast of Western Australia. Dubious records exist from further north (York Sound), and only a single confirmed vagrant specimen has ever been recorded off New Zealand.

This bottom-dwelling species inhabits a wide range of benthic environments, most commonly rocky reefs, but also sandy patches, muddy bottoms, and seagrass beds. It occupies a depth range from close inshore in the intertidal zone down to 275 metres on the continental shelf, though it is most frequently encountered at depths of less than 100 metres.

Daytime shelter is crucial to its habitat selection. The sharks prefer flat areas protected from strong currents, such as overhangs, rocky outcrops, open trenches, and deep caves with sandy floors. During the spring egg-laying period, females specifically utilize shallow, wave-sheltered rocky crevices in 1 to 5 metres of water to wedge and secure their egg cases.

The Port Jackson shark is a nocturnal predator that actively searches for food along the sea floor during the late evening hours, peaking in activity before midnight. Its diet consists predominantly of hard-shelled benthic invertebrates, including sea urchins (such as the black sea urchin *Centrostephanus rodgersi*), molluscs, and crustaceans, as well as small benthic fishes.

To consume these hard-bodied creatures, the shark relies on its specialised heterodont dentition. The small, pointed anterior teeth grab and hold prey, while the large, flat posterior molars crush and grind tough shells. Juveniles possess sharper teeth than adults and feed on a higher proportion of soft-bodied prey.

Juvenile feeding behaviour is particularly distinct: young sharks forage on soft bottoms by sucking in water and sand from the sea floor, sifting out small prey items, and expelling the sand out through their five gill slits. As the sharks mature into adults, their diet shifts toward larger, hard-shelled organisms that require their powerful crushing jaws.