Shark of the month: Epaulette shark

The Epaulette shark (Hemiscyllium ocellatum) is also known as the Walking shark. They owe this name to the fact that they use their fins to walk over coral reefs. Though capable of freely swimming they seem to show a preference for walking across the bottom using paired fins as limbs. Epaulette sharks belong to the species of long-tailed carpet sharks and can be found off the coast of Australia and Papua, Indonesia. Epaulette sharks are largely nocturnal and are most active at low water when they can crawl between isolated tidal pools. These sharks also display a strong resistance to low oxygen (Hypoxic) conditions that occur when tidal pools are isolated from the ocean. In these conditions, blood flow and ventilation rates drop sharply, combined with suppressing non-essential activity and reducing metabolism in certain areas of the brain. Epaulette sharks can survive for over three hours in conditions with less than 5% oxygen without loss of behavioral responsiveness. In laboratory testing these sharks have survived for an hour without oxygen at 30oC, this temperature is far above that at which most hypoxic tolerant organisms are capable.

hemiscyllium_ocellatum_oceanopolis

Credits to Citron / CC-BY-SA-3.0

Anatomy and appearance

Epaulette sharks are usually less than 1m in length, with a slim body and a short head and broad paired fins. The common name for this shark is derived from the large black spot observed on the body behind each pectoral fin, similar to military epaulettes. Adults are light brown on top with indistinct lines and scattered dark spots, while juveniles have alternating light and dark bands which fade with age. Their colouring provides camouflage from predators while the large black spot is hypothesized to act as an eye spot.

Habitat

Epaulette sharks are found across a range from the southern coast of New Guinea down the east and west coasts of Australia, as far south as Sydney. A particularly large population has been observed in the Capricorn Bunker group of the Great Barrier Reef. These sharks are found in shallow water habitat to a maximum depth of 50m. They are regularly observed in tidal pools, coral flats and amongst small coral outcrops.

hemiscyllium_ocellatum_distmap

Diet

Epaulette sharks feed mainly by opportunistic predation on benthic crustaceans, worms and small fish. Though feeding occurs most actively at dawn and dusk, it may occur at any time. Olfactory and electro-receptive senses help locate hidden prey which can be swallowed while sand or other detritus is expelled from gill slits. Hard shelled prey such as crabs are crushed between small triangular teeth.

Population

epaulette

Credits to aquariumdomain.com

Mating in the wild between Epaulette sharks occurs from July to December with females initiating copulation. The females deposit eggs from August to December with each female producing 20 to 50 eggs a year, two at a time every 14 days. Each egg case measures 10cm by 4 cm with the young emerging after 120-130 days at 14-16cm in length. Males and females mature at an age of around 7 years at 54 to 64 cm.

Conservation

The IUCN has assessed the species as “Least Concern”, however in waters off Papua New Guinea habitat destruction, over-fishing and damaging fishing practices have pushed the species to a “Near Threatened” state. In Australia the habitat of this species is largely protected in Marine Protected Areas and across the rest of the species distribution the species is of little to no commercial interest. Small scale collection for the aquarium trade does occur though this is of little impact. These sharks readily acclimatize to captivity and have been observed to breed in local aquaria.

Relationship to humans

Interactions between humans and these sharks have demonstrated a lack of fear by Epaulette sharks with small bites possible if too closely handled, however the species should be regarded as harmless.

Originally written by KY and edited by Isabelle Walter

 

 

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