Australian swellshark
Encyclopedia
- Not to be confused with the draughtsboard sharkDraughtsboard sharkThe draughtsboard shark is a species of catshark, family Scyliorhinidae, so named for its "checkerboard" color pattern of dark blotches. It is endemic to New Zealand, where it is also known as the carpet shark...
, Cephaloscyllium isabellum, of New Zealand.
The Australian swellshark or draughtboard shark (Cephaloscyllium laticeps) is a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of catshark
Catshark
Catsharks are ground sharks of the family Scyliorhinidae, with over 150 known species. While they are generally known as catsharks, many species are commonly called dogfish....
, 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...
Scyliorhinidae, endemic to 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...
. This bottom-dwelling species can be found on the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
down to a depth of 220 m (721.8 ft). Usually measuring 1 m (3 ft) long, it is a stout-bodied, broad-headed shark with a short tail and a 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...
much larger than the second. It can be identified by its variegated dorsal coloration of brown or gray patches and numerous spots.
Australian swellsharks are sedentary and mainly nocturnal, with most individuals remaining within the same local area throughout the year. It feeds on small 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, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
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...
es. When threatened, it responds by rapidly taking in water or air to inflate its body, hence the name "swellshark". This shark is oviparous and females lay pairs of distinctively ridged egg capsules
Mermaid's purse
An egg case or egg capsule, colloquially known as a mermaid's purse or devil's purse, is a casing that surrounds the fertilized eggs of some sharks, skates, and chimaeras. They are among the common objects which are washed up by the sea. They are made of collagen protein strands...
at 20–30 day intervals. The eggs hatch after 11–12 months. Harmless and of little commercial interest
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
, many Australian swellsharks are caught incidentally
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...
in gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
s and bottom trawls but usually survive to be released because of their extreme hardiness. As a result, the International Union for Conservation of Nature (IUCN) has assessed this species as of Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
.
Taxonomy
The first scientific description of the Australian swellshark, as Scyllium laticeps, was published in 1853 by French zoologist Auguste DumérilAuguste Duméril
Auguste Henri André Duméril was a French zoologist. He was professor of Herpetology and Ichthyology at the Muséum National d'Histoire Naturelle in Paris from 1857. His father André Marie Constant Duméril was also a zoologist...
, in the scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
Revue et Magasin de Zoologie. The type specimen was a 79 cm (31.1 in) long male caught off Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
. The specific epithet laticeps is derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
latus, meaning "broad", with the suffix ceps, meaning "head". Other common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s for this species include flopguts (a reference to its ability to inflate), Isabell's swell shark, nutcracker shark, rock shark, sleepy Joe, and spotted swellshark. This species is almost identical to the draughtsboard shark
Draughtsboard shark
The draughtsboard shark is a species of catshark, family Scyliorhinidae, so named for its "checkerboard" color pattern of dark blotches. It is endemic to New Zealand, where it is also known as the carpet shark...
(C. isabellum) 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...
; the two species differ in coloration and the form of their egg cases (ridged in C. laticeps versus smooth in C. isabellum).
Distribution and habitat
The Australian swellshark inhabits the continental shelf of southern Australia, from the Recherche Archipelago off Western AustraliaWestern Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
to Jervis Bay
Jervis Bay
Jervis Bay is a large bay bounded by the state of New South Wales, the Jervis Bay Territory, and a detached enclave of the Australian Capital Territory. HMAS Creswell is located between Jervis Bay Village and Greenpatch in the Jervis Bay Territory.-History:...
in New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
, including Tasmania. It is commonly found on or near the bottom amongst rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s or seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
beds, from close to shore to a depth of 220 m (721.8 ft).
Description
The Australian swellshark has a stocky, rounded body that tapers significantly to the short caudal peduncle. The head comprises no more than a fifth of the total length and is broad and moderately flattened, with a very short, thick, blunt snout. The nostrilNostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s are divided into small incurrent and excurrent openings by short, triangular flaps of skin that do not reach the mouth. The mouth is extremely large, without furrows at the corners. The teeth are numerous and small with multiple cusps; the upper teeth are exposed when the mouth is closed. The large, oval eyes are placed somewhat on the upper surface of the head, and have rudimentary nictitating membrane
Nictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
s (protective third eyelid
Eyelid
An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
s) and ridges underneath.
There are two 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...
s, the first much larger than the second. The first dorsal originates over the forward half of the pelvic fin bases, while the second is located over the anal fin. The pectoral fins are large and broad, and the anal fin is larger than the second dorsal fin. The short and broad caudal fin has an indistinct lower lobe and a prominent ventral notch near the tip of the upper lobe. The skin is thick and covered by well-calcified
Calcification
Calcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...
, arrowhead
Arrowhead
An arrowhead is a tip, usually sharpened, added to an arrow to make it more deadly or to fulfill some special purpose. Historically arrowheads were made of stone and of organic materials; as human civilization progressed other materials were used...
-shaped dermal denticles, which are more sparse in young sharks. The back and sides are light gray to brown, with an irregular pattern of close-set darker saddles and blotches along with many dark (sometimes light) spots, and a dark stripe from under the eye to the pectoral fin origins. The fins do not have sharply lighter margins. The underside is cream-colored, with some mottling on the fins and often a dark stripe running down the middle in adults. The maximum known length is 1.5 m (4.9 ft), though few exceed 1 m (3.3 ft).
Biology and ecology
One of the higher-level predators within its ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
, the Australian swellshark feeds on 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 (particularly crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s and rock lobster
Rock lobster
Jasus edwardsii, the southern rock lobster, red rock lobster, or spiny rock lobster, is a species of spiny lobster found throughout coastal waters of southern Australia and New Zealand including the Chatham Islands. This species is commonly called crayfish or crays in New Zealand and in Māori...
s), cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s (including squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
), and small 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...
es. Even large-sized prey tends to be swallowed whole; the long periods of rest exhibited by some sharks may relate to digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
. Like the other members of its genus, this shark is capable of rapidly inflating its body by taking water or air into its stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, as a defense against predators. These include larger fishes, such as 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), and marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s. By inflating, the shark may be able to wedge itself inside crevices, make itself harder to swallow, or simply intimidate a would-be predator. Marine snails are known to prey upon this shark's eggs. The Australian swellshark serves as a host to a number of parasite species, but these are poorly documented.
Life history
The Australian swellshark is oviparous. Males have larger teeth than females, with which to bite and hold onto them for copulation. Whether there is a specific mating season is uncertain, though in terms of spermSperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
production males are capable of breeding year-round. Females have a single functional ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
and two oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...
s, ovulating
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
a single egg into each at a time. They can store sperm for at least 15 months. Females produce eggs throughout the year, laying them in pairs approximately once every 20 days from January to June, and once every 30 days the rest of the year. The second egg in a pair is deposited 12–24 hours after the first.
The pale, flask-shaped egg capsule
Mermaid's purse
An egg case or egg capsule, colloquially known as a mermaid's purse or devil's purse, is a casing that surrounds the fertilized eggs of some sharks, skates, and chimaeras. They are among the common objects which are washed up by the sea. They are made of collagen protein strands...
s measure 13 cm (5 in) long and 5 cm (2 in) across, and bear 19–27 crosswise ridges. There are long, curling tendrils at the four corners, which allow the female to attach the capsule to seaweed or other bottom structures. In captivity, the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
develops external gills at two months old, which are retained until it is five months old, at which time the internal gills take over and the first pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
ation appears. At six months, embryonic growth accelerates and the yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
begins to shrink, disappearing by nine to ten months of age. Hatching usually occurs at eleven to twelve months; the newly emerged young are miniature versions of the adults measuring 14 cm (6 in) long. Males mature sexually at a length of 71–87 cm (28–34.3 in), and females at 75–86 cm (29.5–33.9 in).
Human interactions
The Australian swellshark is harmless to humans and seldom utilized, though recently in parts of Tasmania some have begun to be marketed as a source of "flakeFlake (fish)
Flake is a term used in Australia to indicate the flesh of any of several species of small shark, particularly Gummy shark. The term probably arose in the late 1920s when the large-scale commercial shark fishery off the coast of Victoria was established. Until that time, shark was generally an...
". It is regarded as a nuisance by lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
fishers due to its habit of entering traps
Lobster trap
Not to be confused with Lobster-tailed potA lobster trap or lobster pot is a portable trap that traps lobsters or crayfish and is used in lobster fishing. A lobster trap can hold several lobsters. Lobster traps are constructed of wire and wood. An opening permits the lobster to enter a tunnel of...
to eat the contents. Every year, substantial numbers of Australian swellsharks are 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...
in the southeast Australian shark gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
fishery, and more in bottom trawls and on longlines. These animals are usually released, and likely suffer minimal mortality due to their resilience. Since this species at present faces little risk from fisheries, the International Union for Conservation of Nature (IUCN) has listed it under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
. Although commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
reported drops in Australian swellshark catches from 1973 to 1976 and 1998 to 2001, these appeared to have resulted from changing fishing habits rather than actual population declines. Nevertheless, as a precaution the government of Tasmania has instituted a possession limit of two sharks per person or five sharks per boat per day.