Port Jackson shark

Port Jackson shark

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The Port Jackson shark, Heterodontus portusjacksoni, is a nocturnal, oviparous type of bullhead
Bullhead shark
The bullhead sharks are a small order of basal modern sharks . There are nine living species in a single genus, Heterodontus, in the family Heterodontidae. All are relatively small, with the largest species being just in adult length...

 shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

 of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Heterodontidae, found in the coastal region of southern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, including the waters off Port Jackson
Port Jackson
Port Jackson, containing Sydney Harbour, is the natural harbour of Sydney, Australia. It is known for its beauty, and in particular, as the location of the Sydney Opera House and Sydney Harbour Bridge...

. It has a large head with prominent forehead ridges and dark brown harness-like markings on a lighter grey-brown body. Port Jackson sharks can grow up to 1.67 metres (5.5 ft) long.

The Port Jackson shark is a migratory
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...

 species, traveling south in the summer and returning north to breed in the winter months. They feed on hard-shelled mollusks, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s, sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...

s, and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

.
Port Jackson Sharks are quite distinctive blunt headed-sharks that lay eggs. Port Jackson Sharks have 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 this species.

Distribution and habitat


The Port Jackson shark is endemic to the waters around Australia—it can be found in southern Australian waters and west of the south central coast of the continent. It is believed to have originated somewhere off the coast of South Africa. On one occasion it has occurred off the coast of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, however it is usually limited into two groups found from Northeastern Victoria to Western Australia and from Southern Queensland to New South Wales. It usually lives less than 100 metres (328.1 ft) underwater, but has been known to go as deep as 275 metres (902.2 ft).

The shark's territory is habitually sited in stone settings on the bottom where it feeds
Bottom feeder
Demersal fish live on or near the bottom of the sea or lakes. They occupy the sea floors and lake beds, which usually consist of mud, sand, gravel or rocks. In coastal waters they are found on or near the continental shelf, and in deep waters they are found on or near the continental slope or along...

. Though rocky environments are the most common sandy and muddy ones are also possibly, probably near seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...

. Since the shark is nocturnal, during the day it resides in low resistance areas such as caves.

Appearance


Port Jackson sharks are similar to other organisms in their genus, bearing a broad, flat head, an anal fin, and crests above its eyes.
However, the species possesses characteristics that make them easily identifiable—their teeth and the harness-like markings which run for a majority of their body length. This feature runs from their eyes to their first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 and then across the rest of their body. Both of its dorsal fins are of close to equal size, each with a spine at the foremost edge. This is rumored to be of poisonous nature. Other features that help distinguish them are their small mouths and their nostrils, which are connected to their mouth.

The sharks have gray-brown bodies covered by black banding, which covers a large portion of their sides and back. One of these band winds over the face and progresses even to 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 back of Port Jackson sharks. These progress from the caudal fin to the first dorsal fin.

Teeth


The teeth of the Port Jackson shark are arguably its most distinguishable feature. Unlike other sharks its teeth are different in the front and back. The frontal teeth are small, sharp and pointed, while the latter is flat and blunt. These teeth are helpful for these species towards it diet, which consists of mollusks and similar organisms; they are perfect for crushing. While they are young, the sharks have sharper teeth.

Respiratory system


The Port Jackson shark has five gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s, 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. The shark possesses behind each eye an accessory respiratory organ called a spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...

. 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
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical 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 20 times more slowly than air 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 have the ability to eat and breathe at the same time. This ability is unusual for sharks which mostly 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.

Reproduction


Male Port Jackson sharks become sexually mature between ages 8 and 10, and females at 11 through 14. They are oviparous meaning that their eggs, which are laid annually, are produced in a group, rather than in live birth
Live birth
In human reproduction, a live birth occurs when a fetus, whatever its gestational age, exits the maternal body and subsequently shows any sign of life, such as voluntary movement, heartbeat, or pulsation of the umbilical cord, for however brief a time and regardless of whether the umbilical cord or...

. Their breeding season begins in August, continuing until the middle of November while the female lays egg pairs off and on for every 10 to 14 days. As many as 8 pairs of offspring can be laid during this period. The eggs mature for 10–11 months before hatching at once from the sac. The babies, known as neonates, have an 89% mortality rate of dying before even being born.

Digestive system


Digestion of food can take a long time in the Port Jackson shark. Food moves from the mouth to the 'J' shaped stomach, where it is stored and initial digestion occurs. Unwanted items may never get any further than the stomach, and are coughed up again. They have the ability to turn their stomachs inside out and spit it out of their mouths in order to get rid of any unwanted contents.
One of the biggest differences in digestion in the shark when compared to mammals is the extremely short intestine. This short length is achieved by the spiral valve
Spiral valve
A spiral valve is the lower portion of the intestine of some sharks, rays, skates and bichirs. A modification of the ileum, the spiral valve is internally twisted or coiled to increase the surface area of the intestine, to increase nutrient absorption....

 with multiple turns within a single short section instead of a very long tube-like intestine. The valve provides a very long surface area for the digestion of food, requiring it to pass around inside the apparently short gut until fully digested, when remaining waste products pass by. The most obvious internal organ in sharks is the huge liver, which often fills most of the body cavity.
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.
When most people think of shark teeth, they think of large, sharp teeth like those in the film 'Jaws'. Not all sharks have teeth like these. The teeth of the Port Jackson Shark are very different. They are not serrated, and the front teeth have a very different shape from those found at the back of the jaws, 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.
Juvenile Port Jackson Sharks have more pointed teeth and feed on a higher proportion of soft-bodied prey than adults. 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.

Relationship with humans


The shark has no major importance to humans. It is not an endangered species whatsoever and cannot be utilized as a food supply. It is, however, useful when scientists are hoping to study bottom-dweller sharks or can be caught as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...

. It also does not pose any danger to humans. In October 2011 a man was 'bitten' by a Port Jackson shark at Elwood
Elwood, Victoria
Elwood is a suburb in Melbourne, Victoria, Australia, 8 km south from Melbourne's central business district. Its Local Government Area is the City of Port Phillip...

 Beach in Melbourne
Melbourne
Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...

. The bite did not pierce the skin and the man was able to swim away while the shark was latched on to his calf.

Conservation


Although listed as "Least Concern" on the World Conservation Union (IUCN) Red List, it is known that the shark's embryos experience very high mortality rate
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...

s (89%). Its status is otherwise, largely unknown. Predators of the species are also unknown. Though Crested bullhead shark
Crested bullhead shark
The crested bullhead shark is an uncommon species of bullhead shark, family Heterodontidae, occurring off eastern Australia from the coast to a depth of . This shark can be distinguished from other members of its family by the large size of the ridges above its eyes and by its color pattern of...

 (Heterodontus galeatus) are known to prey upon Jackson shark embryos, the biggest threat is probably from other sharks such as white sharks and the broadnose sevengill shark
Broadnose sevengill shark
The broadnose sevengill shark is the only extant member of the genus Notorynchus, in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, with the exception of the members of the order Hexanchiformes and the sixgill sawshark.The...

(Notorynchus cepedianus).

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