PORT JACKSON SHARK
Bottom dwellers
The Port Jackson shark is a nocturnal, bottom dwelling ‘bullhead’ shark endemic to the Great Southern Reef.
These sharks grow up to 1.65m and can live for more than 30 years. They usually live at depths of less than 100 metres but have been known to go as deep as 275 metres.
Lone youngsters
The shark's territory is habitually on or near the sea bottom, which is also its feeding area. They use the seagrass areas to camouflage with their pattern markings.
Port Jackson sharks are a nocturnal species and are most active right in the middle of the night. These sharks have a small mouth containing small molar-like teeth in the rear of the mouth to crush prey which may be urchins, crustaceans, molluscs or small fish.
During the day, when they are usually not active, they can be found in flat areas which offer some shelter from currents including caves or near other sheltering positions such as rocky outcrops.
Profile of a PJ
Port Jackson sharks are similar to others of their genus, bearing a broad, blunt, flat head, an anal fin, and crests above its eyes. They are often mistaken for crested horn sharks (which only live across Australia’s East coast).
Identification of this species is very easy due to the pattern of harness-like markings that cross the eyes and run along the side of the shark. They also have a spine in front of both dorsal fins.
Similar to what has been done on seadragons, whale sharks and manta rays researchers are now starting to use photo identification technology on PJ sharks by using photos of the topside of their heads.
“When I started looking at the tops of the heads, I started noticing really distinguishing markings”
- Citizen scientist and PJ shark expert Sue Newson.
Annual migration
Port Jackson Sharks will congregate in large numbers in shallow waters in late spring time to mate. Males arrive first in harbours and bays and females usually arrive weeks later. Mating involves biting, with the male grasping the pectoral fin, dorsal fin or flank of the female and rolling her over.
A migratory species, Port Jackson sharks travel south in the summer months to at the end of their breeding season. Males move into deeper water right after breeding, followed by females after egg laying. Females may migrate as far down as Tasmania but it is unclear exactly where the males go. The sharks return each year completing an annual migration to breed in coastal embayments.
Females lay pairs of corkscrew shaped eggs every one to two weeks. As many as eight pairs can be laid during this period. The yolk sack takes up most of the space inside of the egg. Male Port Jackson sharks become sexually mature around 9 years old, and females around 12.
Ten month wait
As the eggs develop they will start opening up on the top. Every year usually from around January, you may be able to start seeing juveniles developing inside the eggs.
“I noticed the yolk had veins all over it and pulsing like a heartbeat” explained naturalist, citizen scientists and PJ expert Sue Newson.
After 10 months the hatchlings can break out of their egg capsule. They use sheltered bays like Jervis Bay, and Port Noarlunga Reef which act as nursery areas for juveniles. The eggs are highly predated by other PJ sharks, crested horn sharks and other species. Recent studies indicated eggs have a mortality rate of almost 90%, mostly due to this predation.
Egg Image: John Turnbull
Fast Facts:
Family: Heterodontidae (Bullhead shark)
Feeding: Urchins, crustaceans, molluscs or small fish.
Habitat: Shallow rocky reefs, outcrops, caves and deep waters up to 275m
Distribution: Endemic to the Great Southern Reef
Special Power: Crab crushing molar teeth
All images ©Ocean Imaging|Great Southern Reef unless otherwise indicated.
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