PORT JACKSON SHARK

Taxonomy:

Phylum– Chordata

Class– Chondrichthyles

Subclass– Elasmobranchii

Infraclass– Euselachii

Superorder– Selachimorpha

Order– Heterodontiformes

Common Name– Bullhead Sharks

Family– Heterodontidae

Common Name– Bullhead Sharks

Genus– Heterodontus

Species– portusjacksoni

Status: IUCN Red List LEAST CONCERN  

Average Size and Length: They are born between 23-24 cm/ 9.1-9.4 inches. Mature males are between 2.3-2.6 feet. Females have been measured between 2.6-3.1 feet. The maximum recorded has been 5.4 feet. It is thought on rare occasion they could be greater than 7.8 feet. It is one of the largest sharks in its family.

The egg case is between 13-17 cm long by 5-7 cm on the broad end.

Teeth and Jaw: Port Jackson sharks have small mouths. The front or anterior teeth are small, sharp and pointed, while the back or posterior teeth are flat and blunt. These teeth function to hold and break, then crush and grind the shells of the mollusks and echinoderms. Juveniles of the species have sharper teeth.

Head: It has a large, blunt head with crests above its eyes. Behind each eye are small spiracles. The nostrils are connected to their mouths.

Denticles: The Port Jackson shark has large dermal denticles, aligned in a posterior direction. Their skin is often described as tough and rough.

Demographic, Distribution, Habitat, Environment and Range: The Port Jackson shark can be found in southern Australia including the waters off Port Jackson. There is a possibility of a report of one in New Zealand but this isn’t confirmed. They prefer temperate waters in the intertidal zone to at least 902 feet. Continue reading below to understand their migratory behaviors.

A single specimen of the Port Jackson shark was collected in a set net at Makara, Wellington in 1954.

There are some researchers that believe they may have originated somewhere off the coast of South Africa.

Diet: They feed mainly on sea urchins, other benthic invertebrates and small fish. The juvenile diet has a higher proportion of soft-bodied prey than adults.

Predators of the Port Jackson shark themselves are unknown but more than likely other larger sharks. The Crested Bullhead shark (Heterodontus galeatus) are known to prey upon Port Jackson shark embryos by stealing their eggs cleverly disguised as Port Jackson Sharks.

Ram-Suction Index: Port Jackson sharks are high on the suction index. 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.

Aesthetic Identification: Port Jackson sharks are grey to light brown or whiteish with a unique distinctive black striped harness type of marking. One of these bands winds over the face and progresses between and under the shark’s eyes. Another harness-shaped band goes around the back, continuing until the pectoral fins and sides. Thin, dark stripes are also present on the backs of Port Jackson sharks. These progress from the caudal fin to the first dorsal fin. There are no spots. The Port Jackson shark has five gills, the first supports only a single row of gill filaments, while the remaining four support double rows of filaments. Each of the second to the fifth gill arches supports a sheet of muscular and connective tissue called a septum. Both dorsal fins are of close to equal size, each with a spine at the foremost edge. The pectoral fins are large and angular. They do have an anal fin.

Biology and Reproduction: The Port Jackson shark is oviparous with an annual reproduction cycle. The Port Jackson shark’s mating and egg laying happens during the winter. 10-16 eggs are laid in pairs every 8-17 days in rocks or crevices, on sheltered rocky reefs in 3-16 feet. Occasionally they will be deposited deeper between 66-98 feet. Males reach peak sperm production around May, but females do not begin laying eggs until late August. Mating occurs some time prior to laying the eggs and the females store the sperm within their shell glands until ready to fertilize the eggs. The eggs are deposited between August and September. The soft eggs are pointed edge wedged down. The egg cases are auger-shaped. The double helix flange wraps the capsule two to three times beginning with the broad end. At first the case is light brown to olive green, and over a few days it hardens and darkens in color. The eggs hatch 12 months later. The hatchling neonates can break out of the egg capsule. The eggs have been assessed in recent studies as having an 89.1% mortality rate. Predation is the cause. 

It is thought that male Port Jackson sharks become sexually mature between ages 8 and 10 or between 21.7-27.6 inches, and females at 11 to 14 or between 27.6-35.4 inches. Research suggests that they can live more than 30 years.

Genetic studies suggest two Australian groups, one found from Northeastern Victoria to Western Australia and the second found from Southern Queensland to New South Wales.

Diving deep into the biology of the shark, along the top and bottom of each gill filament are delicate, closely packed, transverse flaps of gill tissue known as secondary lamellae. It is these lamellae that are the actual sites of gas exchange. Each lamella is equipped with tiny arteries that carry blood in a direction opposite to that of the water flowing over them. To compensate for the relatively low concentration of dissolved oxygen in seawater, water passes over the secondary lamellae of sharks some 5% as fast as air that remains in contact with the equivalent gas exchange sites, such as the alveoli of the lungs found in humans. This delay allows sufficient time for dissolved oxygen to diffuse into a shark’s blood.

Port Jackson sharks are capable of staying still on the bottom, eating and breathing at the same time. This is not typical of most sharks because they need to swim with their mouths 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. This allows the shark to rest during the day, and also position itself to ambush prey.

Research suggests that digestion of food can take a long time in the Port Jackson shark, like in many other sharks. It is also suggested that they have the ability to turn their stomachs inside out and spit it out of their mouths to get rid of any unwanted contents. One of the biggest differences in digestion of a shark in comparison to mammals is the short intestine. This short length is achieved by the spiral valve with multiple turns within a single short section instead of a very long tube-like intestine. Like most other sharks they also have relatively large livers.

Many parasites have been reported on and within Port Jackson sharks. Some parasites found are nematodes, copepods, leeches, fish lice, cestodes, isopod larvae, and trematodes.

Behavioral Traits, Sensing and Intelligence: The Port Jackson shark rests by day in groups or on the sand or in some selected caves and gullies. The sharks will relocate. They are nocturnal and are actively hunting at night.

They participate in traditional and collective egg laying at dedicated sites. The hatchlings will move to nursery grounds until they reach adolescents. Once reached, they will move offshore and segregate by sex. A few years later they will join the population of adults. The adults also segregate by sex. They also participate in very complex seasonal breeding migrations.

All females will move inshore to reefs in July to breed and some males will as well. The males will return offshore after breeding. The females return after they lay their eggs. Some adults may remain offshore in the summer and others will migrate south up to 528 miles from breeding areas.

The Port Jackson shark is sympatric with the less common Crested Bullhead shark They can be found in the same habitat throughout much of the Crested Bullhead shark’s range. The Crested Bullhead shark, however, is more common in northern/warmer waters than the Port Jackson shark.

Speed: They are slow-moving and sluggish, and more than likely like other sharks in its family use its large pectoral fins to help walk across the seabed.

Port Jackson Shark Future and Conservation: Currently they are of least concern and are plentiful. On occasion they are taken as bycatch, but they are mainly returned alive to the ocean. They are kept and bred in captivity. Although listed as “Least Concern” on the World Conservation Union (IUCN) Red List, the shark’s egg capsules experience very high mortality rates at an estimated at 89.1%. Its status is otherwise largely unknown.

In June 2018 the New Zealand Department of Conservation classified the Port Jackson shark as “Vagrant” with the qualifier “Secure Overseas” under the New Zealand Threat Classification System.

Port Jackson Shark Recorded Attacks on Humans: Harmless to humans (unless stressed), the Port Jackson shark poses no threat. Their spines can impose a painful wound if not careful. In October 2011 a man was ‘bitten’ by a Port Jackson shark at Elwood Beach near Melbourne. The bite did not pierce the skin and the man was able to swim away while the shark was latched on to his calf.