The epaulette shark ( Hemiscyllium ocellatum) is a fascinating species known for its unique 'walking' ability and resilience in shallow reef environments. This article delves into the specifics of the epaulette shark's diet and feeding habits, exploring what they eat, where they forage, and how their behavior adapts to their environment.
Introduction to the Epaulette Shark
The epaulette shark is a small, slender shark species, typically around 1 meter in length. It is easily identified by the large black spot, ringed in white, located on each side of its body, resembling an epaulette. These sharks are commonly found on shallow reefs of Australia and New Guinea, particularly on the Great Barrier Reef, typically no deeper than 40 m. They exhibit a preference for shallow, tidal reef areas. Their ability to move around complex reef structures by 'walking' on their pectoral fins between tidal pools and reef flats is a distinctive feature. They can endure low oxygen levels while out of the water and seem resilient to the higher water temperatures of these shallow habitats.
Habitat and Foraging Behavior
Epaulette sharks mainly feed in reef flats and tidal pools, where they forage in sandy substrates to find their prey. They are primarily bottom feeders and prefer substrates of sand and coral reef growth as source areas for their food. Although they are considered primarily nocturnal, they may be observed searching for food during any part of the day, with their favorite times for feeding at dusk and dawn. This activity pattern helps them avoid some predators and take advantage of the availability of their prey.
Epaulette sharks are commonly found foraging in small tide-pools remotely located from active ocean water. These tide pools characteristically are low in oxygen concentration and unable to support most fish life. Research has shown that this species has the ability to selectively route blood to essential parts of its body, and it also appears that its nerves are designed to function in low oxygen circumstances.
Dietary Preferences
The diet of the epaulette shark primarily consists of polychaete worms, small fish, and crustaceans. Recent studies on this shark’s food preferences indicated that the diet of juveniles tends toward a preference for polychaete worms, while adults seem to prefer crabs. Both groups will also feed on small bony fish and shrimp. As epaulette sharks mature, their diet shifts more from polychaete worms to fish and crabs. Their food choices are mostly limited to various invertebrates.
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Hunting Techniques
Epaulette sharks are most active at dusk and dawn, employing a combination of sensitive nasal barbles and keen electroreception to find their prey in the sand. These adaptations enable them to locate hidden prey in the complex reef environment. They crawl, clamber, and swim about, while thrashing their tail to dig their snout into the sand.
Adaptations for Feeding
Several adaptations allow the epaulette shark to thrive in its unique environment. Special modification of the attachment, skeleton, and musculature of the paddle shaped pectoral and pelvic fins provides strength and allows for a great range of movement, permitting the unique “walking” pattern of this animal. This walking ability is possible through specially adapted paddle-shaped fins that have modified musculoskeletal attachments. This allows them to move between and forage in tidal pools that become separated from the ocean, and which are inaccessible to other predators.
Their tolerance of very low oxygen levels (hypoxia conditions) is another significant adaptation. One study showed that the epaulette was unaffected by an oxygen level of 0.35 mg/L at 75 degrees for 2 hours. This allows them to forage in hypoxic environments.
Reproduction and Early Diet
Females mature at a length of around 0.6 m and are capable of producing up to 50 egg cases per year, although typically only two are produced at a time. Fibrous strands from the eggs help them entangle on the seafloor, and they tend to hatch after a gestation of about 120 days, with new born pups being barely 0.2 m long. The newborn pups are about 15 cm (5.9 in) long. The diet of juvenile epaulette sharks consists mainly of polychaete worms, providing them with the necessary nutrients for growth and development.
Interactions with Humans and Conservation Status
The primary relationship epaulette sharks seem to have with people is fascination - it is a favorite in aquaria and in wildlife documentaries for its unusual walking habit. There is little known exploitation of them, but the extent of their capture in areas such as New Guinea requires further investigation. There is limited exploitation of this species in the bulk of its range in Australia, where it is primarily collected for the aquarium trade.
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They are under some threat in New Guinea from overfishing, habitat destruction and pollution, but there is currently insufficient data and further monitoring is required. Although currently unknown, the impacts of climate change could impact their ability to forage in hypoxic environments and the development of their embryos. Consequently, this species is considered Least Concern by the IUCN, with a stable population.
Physical Characteristics
The epaulette shark is easily recognized. It has a small, slender, almost eel-like form, a short, rounded snout with nasal barbells on the underside, prominent eyes, spiracles, and paddle shaped pectoral and pelvic fins. Two dorsal fins of similar size are located well back on the body. The anal fin is located just forward of the caudal fin. The caudal fin is narrow and has no ventral lobe. The caudal peduncle (to which the tail fin is attached) comprises over half the shark’s length. There are 26 to 35 tooth rows in the upper jaw and 21 to 32 tooth rows in the lower jaw. The base body color is a creamy or slightly brownish hue. An easily located identifying characteristic from which the fish derives its name, is a large, black, false eyespot, ringed in white, located on each side of the fish above the trailing edge of the pectoral fins. The body is marked with widely spaced dark brown spots. Epaulette sharks are typically 70 to 90 cm (27 to 35 in) long.
Additional Facts
Epaulette sharks are able to walk, both along the seafloor and across land, for short distances due to specially adapted pectoral fins and musculature. They are also capable of surviving on very little oxygen for up to an hour and tolerating increased temperatures while foraging on reef flats and in tidal pools.
When feeding, most sharks swallow their prey whole or if it is too large, will bite off large chunks and swallow them whole; however, the epaulette shark is sometimes observed chewing its food with a small portion sticking out of its mouth.
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