Epaulette shark
Encyclopedia
The epaulette shark is a species of longtailed carpet shark
, family
Hemiscylliidae, found in shallow, tropical waters off Australia
and New Guinea
(and possibly elsewhere). The common name
of this shark comes from the very large, white-margined black spot behind each pectoral fin, which are reminiscent of military epaulette
s. A small species usually under 1 m (3.3 ft) long, the epaulette shark has a slender body with a short head and broad, paddle-shaped paired fins. The caudal peduncle (to which the tail fin is attached) comprises over half the shark's length. Adults are light brown above, with scattered darker spots and indistinct saddles.
Epaulette sharks have nocturnal habits and frequent shallow water on coral reef
s or in tidal pools. This shark has evolved to cope with the severe nighttime oxygen
depletion (hypoxia
) in isolated tidal pools by increasing the blood supply to its brain and selectively shutting down non-essential neural functions. It is capable of surviving complete anoxia for an hour without ill effects, and at a much higher temperature than most other hypoxia-tolerant animals. Rather than swim, epaulette sharks "walk" by wriggling their bodies and pushing with their paired fins. This species feeds on a wide range of small benthic invertebrate
s and bony fishes. Epaulette sharks are oviparous, with females depositing pairs of egg capsules around every 14 days from August to December. Due to their hardiness and small size, epaulette sharks are popular with both public
and home aquaria
. The International Union for Conservation of Nature (IUCN) has assessed this species as of Least Concern
, as outside of the small aquarium trade it is of little interest to fisheries
.
Pierre Joseph Bonnaterre
in the 1788 Tableau encyclopédique et méthodique des trois règnes de la nature
. The name was later changed to the currently valid Hemiscyllium ocellatum. The type specimen was a 35 cm (14 in) long immature male caught near Cookstown
, Queensland
, Australia
. Other common names for this species are the itar shark and the blind shark (also used for Brachaelurus waddi). Goto's 2002 morphological
analysis of the carpet shark
s showed the genus Hemiscyllium as a polytomy
, meaning that the phylogenetic relationships between the epaulette shark and its sister species could not be resolved.
to the northern coast of Australia
, as far south as Sydney
. The Capricorn-Bunker Group of the Great Barrier Reef
contains a particularly large population, with thousands estimated to inhabit the reefs around Heron Island alone. Additionally, there are unsubstantiated reports of this species from Malaysia, Sumatra
, and the Solomon Islands
. Epaulette sharks are found in shallow water to a maximum depth of 50 m (160 ft), and are often seen in water barely deep enough to cover their bodies. They prefer tidal pools, coral flat
s, and stands of staghorn coral
.
The epaulette shark has an elongated body, over half of which is comprised by the slender caudal peduncle. The snout is short and rounded, with the nares placed almost at the tip along with a pair of tiny barbels
; there are grooves running from the nares to the mouth. There are 26–35 tooth rows in the upper jaw and 21–32 tooth rows in the lower jaw. The teeth are small, with broad bases and triangular cusps. The eyes are oval in shape and elevated, with a large spiracle
below each. The five pairs of gill slit
s are small, with the fourth and fifth very close together.
The pectoral and pelvic fins are broad and rounded and are thickly muscled. The two similarly-sized dorsal fin
s are placed well back on the body. The anal fin is low and positioned just in front of the caudal fin. The caudal fin has only an upper lobe, which contains a prominent ventral notch near the tip and is angled almost horizontally relative to the body. Adult epaulette sharks are beige to brownish above with many widely-spaced brown spots and subtle darker bands. There is a very large black spot ringed in white located behind each pectoral fin; this pair of spots are the origin of this shark's common name. Juveniles have alternating light and dark bands over their body and fins, which break up as they mature. Epaulette sharks are typically 70–90 cm (27–35 in) long; the maximum reported length is 107 cm (42 in).
for navigating its complex reef environment, the epaulette shark moves by seemingly walking, bending its body from side-to-side and pushing off of the substrate with its paddle-shaped pectoral and pelvic fins. The shark only swims to escape from a threat, and then not very far. The cartilaginous
supports of the epaulette shark's paired fins are reduced and separated when compared to other sharks, allowing them to be rotated for use as limbs. This mode of locomotion even enables the shark to crawl out of the water to access isolated tidal pools. The gait of the epaulette shark is convergently
similar to those of tetrapod
s such as salamander
s, suggesting that the movements needed for walking on land may predate, and facilitated the evolution of, the first terrestrial vertebrate
s. Epaulette sharks are largely nocturnal and are most active in low water. They often hide inside or below coral heads, though it is enough for the head to be covered even if the rest of the body is exposed. Sometimes they perch in the open on sandy flats or atop reefs facing into the current, a form of orientation known as rheotaxis that may improve respiration
or predator awareness.
Epaulette sharks are preyed upon by larger fishes such as other sharks. Its coloration provides protective camouflage
, while its epaulette is speculated to be an eyespot
for distracting or deterring predators. Epaulette sharks are almost all parasitized by the praniza (parasitic) larva
l stage of gnathiid
isopods. The larvae feed on blood
and mostly attach to the skin around the cloaca
and the claspers, though they are also found inside the mouth and on the gills. These parasites cause little damage and are not believed to adversely affect the health of the shark. Other parasites of this species include a species of myxosporea
n in the genus Kudoa, which infests the skeletal muscle
s, the hemogregarine protozoan Haemogregarina hemiscyllii, which infects the blood, the ostracod
Sheina orri, which attaches to the gills, and the nematode
Proleptus australis, which infests the stomach.
At night, the shallow reef platforms inhabited by the epaulette shark often become isolated from the ocean by the receding tide. The amount of dissolved oxygen in the pool can drop 80% or more overnight from the combined respiration of all the organisms within the pool. The epaulette shark has evolved to cope with these hypoxic conditions, being able to survive for over three hours in 5% of the atmospheric O2 level without losing behavioral responsiveness. In the laboratory, epaulette sharks have survived for an hour without any oxygen at 30°C (86°F), which is also unusual in that most animals capable of tolerating oxygen deprivation do so at low temperatures.
The physiological responses of the epaulette shark to low oxygen are mediated by the nucleoside
adenosine. In hypoxic conditions, the heart and ventilation rates drop sharply. The shark's blood pressure
falls by half as the blood vessel
s dilate to deliver more blood to the brain and heart. Unlike in bony fishes and tetrapods, the blood flow rate remains constant and there is no elevation of blood glucose
levels. The brains of sharks only consume a third as much ATP
as those of teleosts. The epaulette shark is able to lower this energy demand further by reducing the metabolism
of certain areas of its brain, e.g. keeping the sensory nuclei functional while deactivating the motor nuclei. This allows the shark to supply enough ATP to prevent neuron
death, while still remaining alert to its environment.
s, with juveniles taking mostly the former and adults mostly the latter. It hunts most actively at dawn and dusk, though feeding can occur at any time during the day. This shark relies mainly on its olfactory
and electroreceptive senses to locate hidden prey. It is capable of sucking prey into its mouth by expanding its muscular buccal cavity. While searching for food, the epaulette shark sometimes turns over debris with its snout or thrusts its head into the sand, swallowing food items while expelling the sand grains through its gill slits. Unlike most sharks, the epaulette shark may chew
its food for up to 5–10 minutes. Its teeth can be depressed to form a flat surface for crushing hard-shelled prey.
in the epaulette shark takes place from July to December, though in captivity reproduction occurs continuously. Courtship may be initiated by the female following and biting the male. The male then holds onto the pectoral fin of the female with his mouth and lies alongside her, while inserting one of his claspers into her cloaca
. Copulation lasts about one and a half minutes. This species is oviparous, with females depositing eggs from August to December. The female drops the egg capsules two (rarely four) at a time every 14 days, producing a total of 20–50 eggs per year. Each egg case measures 10 cm (3.9 in) long and 4 cm (1.6 in) wide. The young emerge after 120–130 days, at a length of 14–16 cm (5.5–6.3 in). The growth rate of the young is slow at first but increases to about 5 cm (2 in) per year after three months. Both males and females mature sexually at a length of 54–64 cm (21–25 in), corresponding to an age of at least seven years.
Epaulette sharks are harmless to humans, though if handled they may nip their captors. They are easily captured by beachgoers as they move slowly and show little fear of humans; the shark is often injured by these encounters. This species adapts readily to captivity and is displayed by many public aquariums in the United States, Canada, and Australia. In an article for Aquarium Fish Magazine, Scott W. Michael referred to the epaulette shark as "the best shark for the home aquarium." They will breed in captivity, even in tanks as small as 510 L (135 gal), though full-grown sharks are best housed in tanks of 680 L (180 gal) or more. They are not compatible with community tanks as they will eat other fish.
The International Union for Conservation of Nature (IUCN) has assessed the epaulette shark as of Least Concern
. This species is common in Australian waters, where it is not captured by either commercial
or recreational fisheries
, and is minimally affected by collection for the aquarium trade and fishery bycatch
. Much of its Australian habitat is encompassed by protected marine parks. Off New Guinea, the epaulette shark has been assessed as Near Threatened
, as there it faces habitat degradation, destructive fishing practices
, and over-exploitation
by artisan fishers.
Hemiscylliidae
Hemiscylliidae is a family of sharks in the order Orectolobiformes, commonly known as longtail carpet sharks or bamboo sharks. They are found in shallow waters of the tropical Indo-Pacific....
, 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...
Hemiscylliidae, found in shallow, tropical waters off 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...
and New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
(and possibly elsewhere). The 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...
of this shark comes from the very large, white-margined black spot behind each pectoral fin, which are reminiscent of military epaulette
Epaulette
Epaulette is a type of ornamental shoulder piece or decoration used as insignia of rank by armed forces and other organizations.Epaulettes are fastened to the shoulder by a shoulder strap or "passant", a small strap parallel to the shoulder seam, and the button near the collar, or by laces on the...
s. A small species usually under 1 m (3.3 ft) long, the epaulette shark has a slender body with a short head and broad, paddle-shaped paired fins. The caudal peduncle (to which the tail fin is attached) comprises over half the shark's length. Adults are light brown above, with scattered darker spots and indistinct saddles.
Epaulette sharks have nocturnal habits and frequent shallow water on coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s or in tidal pools. This shark has evolved to cope with the severe nighttime oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
depletion (hypoxia
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
) in isolated tidal pools by increasing the blood supply to its brain and selectively shutting down non-essential neural functions. It is capable of surviving complete anoxia for an hour without ill effects, and at a much higher temperature than most other hypoxia-tolerant animals. Rather than swim, epaulette sharks "walk" by wriggling their bodies and pushing with their paired fins. This species feeds on a wide range of small benthic invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s and bony fishes. Epaulette sharks are oviparous, with females depositing pairs of egg capsules around every 14 days from August to December. Due to their hardiness and small size, epaulette sharks are popular with both public
Public aquarium
A public aquarium is the aquatic counterpart of a zoo, housing living aquatic species for viewing. Most public aquariums feature tanks larger than those kept by home aquarists, as well as smaller tanks. Since the first public aquariums were built in the mid-19th century, they have become popular...
and home aquaria
Fishkeeping
Fishkeeping is a popular hobby concerned with keeping fish in a home aquarium or garden pond. There is also a fishkeeping industry, as a branch of agriculture.-Types of fishkeeping systems:...
. 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...
, as outside of the small aquarium trade it is of little interest to fisheries
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
.
Taxonomy and phylogeny
The epaulette shark was originally described as Squalus ocellatus by the French naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Pierre Joseph Bonnaterre
Pierre Joseph Bonnaterre
Abbé Pierre Joseph Bonnaterre was a French naturalist who contributed sections on cetaceans, mammals, birds, reptiles, amphibians, and insects to the Tableau encyclopédique et méthodique...
in the 1788 Tableau encyclopédique et méthodique des trois règnes de la nature
Tableau encyclopédique et méthodique
The Tableau encyclopédique et méthodique des trois regnes de la nature was an illustrated encyclopedia of plants, animals and minerals, notable for including the first scientific descriptions of many species, and for its attractive engravings. It was published in Paris by Charles Joseph Panckoucke,...
. The name was later changed to the currently valid Hemiscyllium ocellatum. The type specimen was a 35 cm (14 in) long immature male caught near Cookstown
Cookstown
Cookstown may refer to either of the following:*Cookstown, County Tyrone, Northern Ireland*Cookstown, Ontario, Canada*Cookstown, New Jersey, United States...
, Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
, 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...
. Other common names for this species are the itar shark and the blind shark (also used for Brachaelurus waddi). Goto's 2002 morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
analysis of the carpet shark
Carpet shark
The carpet sharks are an order, Orectolobiformes, of sharks, so called because many members have ornate patterns reminiscent of carpets....
s showed the genus Hemiscyllium as a polytomy
Polytomy
A polytomy , meaning many temporal based branches, is a section of a phylogeny in which the evolutionary relationships can not be fully resolved to dichotomies. In a phylogenetic tree, a polytomy is represented as a node which has more than two immediate descending branches...
, meaning that the phylogenetic relationships between the epaulette shark and its sister species could not be resolved.
Distribution and habitat
The range of the epaulette shark extends from the southern coast of New GuineaNew Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
to the northern coast of 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...
, as far south as Sydney
Sydney
Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...
. The Capricorn-Bunker Group of the Great Barrier Reef
Great Barrier Reef
The Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...
contains a particularly large population, with thousands estimated to inhabit the reefs around Heron Island alone. Additionally, there are unsubstantiated reports of this species from Malaysia, Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...
, and the Solomon Islands
Solomon Islands
Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...
. Epaulette sharks are found in shallow water to a maximum depth of 50 m (160 ft), and are often seen in water barely deep enough to cover their bodies. They prefer tidal pools, coral flat
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s, and stands of staghorn coral
Staghorn coral
The Staghorn coral is a branching coral with cylindrical branches ranging from a few centimetres to over two metres in length and height. It occurs in back reef and fore reef environments from 0 to 30 m depth. The upper limit is defined by wave forces, and the lower limit is controlled by...
.
Description
Barbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
; there are grooves running from the nares to the mouth. There are 26–35 tooth rows in the upper jaw and 21–32 tooth rows in the lower jaw. The teeth are small, with broad bases and triangular cusps. The eyes are oval in shape and elevated, with a large 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...
below each. The five pairs of gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are small, with the fourth and fifth very close together.
The pectoral and pelvic fins are broad and rounded and are thickly muscled. The two similarly-sized 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 are placed well back on the body. The anal fin is low and positioned just in front of the caudal fin. The caudal fin has only an upper lobe, which contains a prominent ventral notch near the tip and is angled almost horizontally relative to the body. Adult epaulette sharks are beige to brownish above with many widely-spaced brown spots and subtle darker bands. There is a very large black spot ringed in white located behind each pectoral fin; this pair of spots are the origin of this shark's common name. Juveniles have alternating light and dark bands over their body and fins, which break up as they mature. Epaulette sharks are typically 70–90 cm (27–35 in) long; the maximum reported length is 107 cm (42 in).
Biology and ecology
As an adaptationAdaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
for navigating its complex reef environment, the epaulette shark moves by seemingly walking, bending its body from side-to-side and pushing off of the substrate with its paddle-shaped pectoral and pelvic fins. The shark only swims to escape from a threat, and then not very far. The cartilaginous
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
supports of the epaulette shark's paired fins are reduced and separated when compared to other sharks, allowing them to be rotated for use as limbs. This mode of locomotion even enables the shark to crawl out of the water to access isolated tidal pools. The gait of the epaulette shark is convergently
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
similar to those of tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s such as salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s, suggesting that the movements needed for walking on land may predate, and facilitated the evolution of, the first terrestrial vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s. Epaulette sharks are largely nocturnal and are most active in low water. They often hide inside or below coral heads, though it is enough for the head to be covered even if the rest of the body is exposed. Sometimes they perch in the open on sandy flats or atop reefs facing into the current, a form of orientation known as rheotaxis that may improve respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
or predator awareness.
Epaulette sharks are preyed upon by larger fishes such as other sharks. Its coloration provides protective camouflage
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
, while its epaulette is speculated to be an eyespot
Eyespot (mimicry)
An eyespot is an eye-like marking. They are found on butterflies, reptiles, birds and fish. In members of the Felidae family , the white circular markings on the backs of the ears are termed ocelli, and they are functionally similar to eyespots in other animals.Eyespots may be a form of...
for distracting or deterring predators. Epaulette sharks are almost all parasitized by the praniza (parasitic) larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l stage of gnathiid
Gnathiidae
Gnathiidae is a family of isopod crustaceans. They occur in a wide range of depths, from the littoral zone to the deep sea. The adults are associated with sponges and may not feed...
isopods. The larvae feed on blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
and mostly attach to the skin around the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
and the claspers, though they are also found inside the mouth and on the gills. These parasites cause little damage and are not believed to adversely affect the health of the shark. Other parasites of this species include a species of myxosporea
Myxosporea
The Myxosporea are a class of microscopic parasites, belonging to the Myxozoa. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate and an ectothermic vertebrate, usually a fish. Each host releases a different type of spore...
n in the genus Kudoa, which infests the skeletal muscle
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
s, the hemogregarine protozoan Haemogregarina hemiscyllii, which infects the blood, the ostracod
Ostracod
Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 65,000 species have been identified, grouped into several orders....
Sheina orri, which attaches to the gills, and the nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
Proleptus australis, which infests the stomach.
Hypoxia tolerance
The physiological responses of the epaulette shark to low oxygen are mediated by the nucleoside
Nucleoside
Nucleosides are glycosylamines consisting of a nucleobase bound to a ribose or deoxyribose sugar via a beta-glycosidic linkage...
adenosine. In hypoxic conditions, the heart and ventilation rates drop sharply. The shark's blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
falls by half as the blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s dilate to deliver more blood to the brain and heart. Unlike in bony fishes and tetrapods, the blood flow rate remains constant and there is no elevation of blood glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
levels. The brains of sharks only consume a third as much ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
as those of teleosts. The epaulette shark is able to lower this energy demand further by reducing the metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
of certain areas of its brain, e.g. keeping the sensory nuclei functional while deactivating the motor nuclei. This allows the shark to supply enough ATP to prevent neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
death, while still remaining alert to its environment.
Feeding
The epaulette shark is an opportunistic predator of benthic crustaceans, worms, and small bony fishes. Off Heron Island, over 90% of the epaulette shark's diet consists of polychaete worms and crabCrab
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, with juveniles taking mostly the former and adults mostly the latter. It hunts most actively at dawn and dusk, though feeding can occur at any time during the day. This shark relies mainly on its olfactory
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
and electroreceptive senses to locate hidden prey. It is capable of sucking prey into its mouth by expanding its muscular buccal cavity. While searching for food, the epaulette shark sometimes turns over debris with its snout or thrusts its head into the sand, swallowing food items while expelling the sand grains through its gill slits. Unlike most sharks, the epaulette shark may chew
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
its food for up to 5–10 minutes. Its teeth can be depressed to form a flat surface for crushing hard-shelled prey.
Life history
MatingMating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
in the epaulette shark takes place from July to December, though in captivity reproduction occurs continuously. Courtship may be initiated by the female following and biting the male. The male then holds onto the pectoral fin of the female with his mouth and lies alongside her, while inserting one of his claspers into her cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
. Copulation lasts about one and a half minutes. This species is oviparous, with females depositing eggs from August to December. The female drops the egg capsules two (rarely four) at a time every 14 days, producing a total of 20–50 eggs per year. Each egg case measures 10 cm (3.9 in) long and 4 cm (1.6 in) wide. The young emerge after 120–130 days, at a length of 14–16 cm (5.5–6.3 in). The growth rate of the young is slow at first but increases to about 5 cm (2 in) per year after three months. Both males and females mature sexually at a length of 54–64 cm (21–25 in), corresponding to an age of at least seven years.
Human interactions
The International Union for Conservation of Nature (IUCN) has assessed the epaulette shark 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...
. This species is common in Australian waters, where it is not captured by either commercial
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...
or recreational fisheries
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
, and is minimally affected by collection for the aquarium trade and fishery 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...
. Much of its Australian habitat is encompassed by protected marine parks. Off New Guinea, the epaulette shark has been assessed as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
, as there it faces habitat degradation, destructive fishing practices
Destructive fishing practices
The phrase destructive fishing practices has been featured in international fisheries literature for around three decades. No widely accepted definition of the phrase exists, and this will almost certainly remain the situation, given very different national and industry perspectives...
, and over-exploitation
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
by artisan fishers.