Species - hemiscyllium ocellatum epaulette shark was discovered by Bonnaterre in 1788, Family – Hemiscylliidae, Classification - elasmobranchii, orectolobiformes, hemiscylliidae
Epaulette sharks are found in shallow waters of the Great Barrier Reef in the northeast corner of Australia to New Guinea. This species is a slender fish with an elongated and thick precaudal tail. The epaulette is easily identified by two large black spots surrounded by white above and slightly behind each pectoral fin. These sharks are small and are usually less than 1m. They use electroreception (detect electric fields) and olfaction (the sense of smell) to search for their prey. The species generally feeds at night in shallow tidal pools in and around coral reefs. These waters are often anoxic (low in oxygen) because these pools do not mix well with the surrounding seawater. The epaulette has adapted to live in these conditions and can remain without oxygen for up to an hour with no ill effects (11). The epaulette generally wriggles and walks when it is searching for its prey and lives off small benthic organisms (organisms living on the sea floor or just beneath the substrate) (6).
Epaulette sharks are most often found foraging in small tide-pools and in shallow waters near coral reefs (2). They are primarily bottom feeders and prefer areas where there are coral reefs that harbor their food choices of various invertebrates. These invertebrates consist mostly of worms and crabs (6). Unless they are looking for food, these sharks remain motionless on the sand or concealed in rocky crevices (10).
They are an oviparous species where a pair of eggs develop and are deposited about every 14 days (10).
The shark is recognized by its small and slender form and short rounded snout with prominent eyes, pectoral and pelvic fins (3). They are marked with dark brown spots (3).
Larger fish such as sharks and groupers are their natural predators. They are not on the endangered species list because they have very little commercial value (3). Aquariums on the other hand use these fish because they are small and fit well into their small public displays. However, the over-collection of this species from the wild does not pose a significant threat since they reproduce well in captivity (1). This species is often infested with gnathiid isopod (terrestrial crustaceans, having seven pairs of legs) larvae called praniza (6).
The species has an elongated lateral body shape flattened on the bottom near the snout. There are two lateral large spots just above the dorsal fins that are outlined with white. Much smaller spots are randomly scattered on the rest of the body and head (2).
The epaulette shark's maximum length is 107cm (2).
The epaulette shark is included in the long tail carpet sharks family, Hemiscylliidae (4). The family contains two other species: the speckled carpet shark and the grey carpet shark (4). The epaulette shark and the speckled carpet shark look very similar (4). The epaulette shark can be distinguished by the presence of two large dark spots (ocelli) above the pectoral fins similar to the speckled carpet shark, but with white borders surrounding the ocellus (4). Furthermore, the speckled carpet shark has more small dark spots on its head and body, while the epaulette has fewer more widely spaced spots (4). The epaulettes also have a longer, flatter snout and a more slender body.
Habitat and Ecology
An oviparous species with males and females maturing at 54 to 62 cm TL. Mating probably occur between July and November, with females carrying eggcases found between August and December, although in captivity they have been noted to breed continuously (West and Carter 1990). Two egg capsules are produced and deposited among coral at night. A pair of egg capsules may be produced every 14 days, resulting in up to about 20 potential offspring per female per annum. Eggs hatch after about 120 days with young at 14 to 16 cm TL. Subsequent growth is initially slow, but reaches about five cm year-1 after about three months (West and Carter 1990). Epaulette sharks descend into deeper water between coral reefs and have been found at depths of at least 40 m. The species is hypoxia tolerant and is able to survive in anoxic waters. This trait is important as this shark is often found in shallow (ca 15 cm deep), warm (ca 30°C) waters that become severely hypoxic during the night. This trait may enable this species to survive in areas of poor water quality, such as mining run-off in New Guinea.
The epaulette shark lives in shallow reef flat environments and tidal waters where it is has adapted to live in anoxic conditions (1).
There is evidence of movement from one local reef to another, but studies show that these sharks stay in close proximity to their local habitat (8). Their food source is also non-migratory, so there is no need for epaulettes to migrate. Epaulette sharks are sluggish animals that crawl on the substrate and the placement of their fins may physically prevent them from swimming long distances (8).
Unlike many other sharks, the epaulette sharks have no predictable pattern of movement in and out of their communities (8). The random movement suggests that these sharks stay in their habitat as long as the reefs are stable, and harbor abundant benthic organisms (the prey of the epaulette shark) (8).
The shark’s diet consists of benthic organisms (animals living on the sea floor) that it gets by burying its head in the sand or catching on the surface of the substrate (6). Annelids (segmented worms) and crabs account for most of the food for this species, although there is some shift to shrimp as the shark matures (6). The epaulette shark's diet reveals its important role in structuring reef flat communities on the Great Barrier Reef (8). Population estimates indicate that the epaulette is abundant in these communities, and therefore is likely to be an important predator of invertebrates in the reef flat environment (6).
Life History and Behavior
Epaulette sharks spend most of their time close to the sandy bottom near coral reefs (1). Unless scouting for food, they can remain motionless on the sand or concealed in rocky crevices (1). They blend in easily with the coral because of their intricate camouflage (1).
Epaulettes are mostly bottom feeders and although they are considered nocturnal, they may be observed searching for food during the day (1). They are usually found hiding inside or below coral heads facing into the current, a form of orientation known as "rheotaxis" that may improve respiration or predator awareness (9). These sharks are known for "crawling" on the sea floor using their pectoral and pelvic fins (5). Once they catch their prey, these sharks usually chew their food before ingesting it (4).
Epaulette sharks can live in low oxygen concentrations. When the tide lowers at night, the water on the reef flat that surrounds the island does not mix well with the ocean water which causes an anoxic (low oxygen) condition in the water (11). The flora and fauna in the area can lower their oxygen concentrations from the normal oxygen level of 6.7 mg O2/L to a hypoxic level of 2.1 mg 02/L. The epaulette shark has an increased capacity to survive in these conditions that exist off the northeast corner of Australia near Heron Island (11).
The brownbanded bamboo shark, a close relative of the epaulette shark, lives approximately 25 years (4). It is expected that the epaulette shark would live to be about the same age.
Not much is known about reproduction in the wild, but there is some data on the sharks in captivity (7). While females sexually mature at an average length of about 64.3cm (3), males mature when they are about 59-62cm (2). The species is oviparous and reproduces by laying eggs (7). Males grasp the female’s pectoral fins or body in its mouth to stabilize the pair during the process (10). Two eggs are produced from each breeding episode with one embryo in each egg (7). Females may produce up to 50 eggs per year (7). By measuring the shark's hormone levels it was estimated that females lay eggs from August to January, while males appear to have swollen claspers from July through December. The males had a high amount of sperm storage in the months of August through November (7). After eggs are released into the water, a fibrous material on one side of the egg will commonly become entangled in coral to stabilize its location (7). The embryos gain nourishment solely from their yolk sacs. After four months, the eggs hatch with juveniles measuring around 15cm long (10). There is no parental care after the egg case is deposited (7).
The egg cases of the epaulette shark are 10cm long and 4cm wide and it takes about 120 days for them to hatch. Once the eggs hatch, the young measure about 15cm. During the first year growth is slow. Maturity is reached at about 60-70cm. (4)
The shark is golden brown to tan in color with widely spaced brownish-black spots encircled with white edges (1). These attributes allow the epaulette to camouflage itself with the ocean floor (1). There is a large black spot surrounded by a white ring above the pectoral fins (3). Young epaulette sharks have bands above the pectoral fins that change into spots when the fish matures (4). Typically the males are about 60cm in length while the females are 64cm in length at maturity. The maximum reported length of an epaulette shark is 107cm (4).
There are two dorsal fins located on the body. The anal fin is located just forward of the caudal fin (4). The teeth are small with broad bases, and are triangular in shape (4). This species is a bottom feeder and is commonly encountered in shallow coral reef areas of tidal waters (4).
Evolution and Systematics
Heart, arteries, lungs, and cells of blind shark allow survival in low oxygen by reducing respiration rate.
"The epaulette shark (Hemiscyllium ocellatum) is a tropical marine vertebrate. It lives on shallow reef platforms that repeatedly become cut off from the ocean during periods of low tides. During nocturnal low tides, the water [O2] can fall by 80% due to respiration of the coral and associated organisms. Since the tides become lower and lower over a period of a few days, the hypoxic exposure during subsequent low tides will become progressively longer and more severe. Thus, this shark is under a natural hypoxic preconditioning regimen. Interestingly, hypoxic preconditioning lowers its metabolic rate and its critical PO·. Moreover, repeated anoxia appears to stimulate metabolic depression in an adenosine-dependent way." (Nilsson and Renshaw 2003:3131)
Learn more about this functional adaptation.
Molecular Biology and Genetics
Statistics of barcoding coverage: Hemiscyllium ocellatum
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
- Needs updating
The epaulette shark is listed as "Least Concern" with the World Conservation Union (IUCN). A status of "Least Concern" means that the species does not qualify for "Critically Endangered", "Endangered", "Vulnerable" or "Near Threatened" (1).
The population trend of the epaulette shark is stable (1).
The epaulette shark is not considered a sport fish so it is generally not targeted for that purpose (1). However, the collection of this species for aquarium trade could be a significant threat (1). The aquariums in the USA are the largest market for this species (1). Furthermore, their hypoxic ability (ability to withstand low oxygen conditions) may help their survivability in less cared for private facilities, thus making it more attractive to smaller aquariums. With improvements in technology and science, major aquariums have been able to reproduce epaulette sharks successfully (1). Therefore, there is less of a demand for these sharks in the wild (1).A serious threat to epaulette sharks is the incidental catch along with food value fish by means of artisanal fishing techniques (coastal or island ethnic groups using traditional techniques such as throw nets) (1). This is especially happening in and around New Guinea where even dynamite is used as a fishing aid (1). The dynamite damages coral reefs which is the epaulette shark's habitat (1). The species is abundant in Australia and is not threatened with extinction globally, however it is “Near Threatened” near and around New Guinea (1).
Relevance to Humans and Ecosystems
Epaulette sharks are popular in the aquarium trade due to their small size. They fit well into artificial habitats and reproduce readily in captivity (1).
The epaulette shark (Hemiscyllium ocellatum) 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 epaulettes. 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 reefs 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 invertebrates 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.
Taxonomy and phylogeny
The epaulette shark was originally described as Squalus ocellatus by the French naturalist 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 sharks showed the genus Hemiscyllium as a polytomy, 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 Guinea 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 flats, 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 slits 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 fins 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 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 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 tetrapods such as salamanders, suggesting that the movements needed for walking on land may predate, and facilitated the evolution of, the first terrestrial vertebrates. 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) larval 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 myxosporean in the genus Kudoa, which infests the skeletal muscles, 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 vessels 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.
The epaulette shark is an opportunistic predator of benthic crustaceans, worms, and small bony fish. Off Heron Island, over 90% of the epaulette shark's diet consists of polychaete worms and crabs, 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.
Mating 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.
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