Tawny nurse shark (Nebrius ferrugineus)
|Size||Total length: up to 320 cm (2)|
Classified as Vulnerable (VU) on the IUCN Red List (1).
The most remarkable feature of the tawny nurse shark is probably its curious ability to change colour between grey and sandy brown depending on the colour of its surroundings (3). The tawny nurse shark is uniformly grey to tan-brown on its upper surfaces, paling slightly on the belly (2) (4). Juveniles can be distinguished from adults by the presence of small dark spots on the skin (4). This large shark has a broad, flattened head with a squarish snout and tiny eyes (3). There are two angular dorsal fins close to the tail, the pectoral fins curve backwards, and the long, narrow tail has a large upper lobe and almost no distinct lower lobe (4) (5).
The tawny nurse shark is widely distributed across the Indian and west and central Pacific Oceans, ranging from the Red Sea, East Africa and the Arabian Gulf to southern Japan, south through Indonesia to Australia (1) (2) (5).
This is a continental and insular shelf species restricted to a narrow band of shallow water from intertidal waters to depths of up to 70 m (1) (2) (4). The tawny nurse shark lives on or near the bottom in lagoons, or close to coral and rocky reefs (2). Like other nurse sharks, this species uses crevices and caves for shelter (5).
This primarily nocturnal shark usually forages for food at night, and rests under reef overhangs and caves during the day in small groups, often piled across or on top of one another (2) (4). At night, the species feeds on a variety of bottom-dwelling lobsters, crabs, octopus and sea urchins, as well as small fishes, usually returning to the same area each morning to rest (2) (4).
The tawny nurse shark is ovoviviparous, with females giving birth to up to eight live young that have hatched within the uterus (4).
The shallow water that the tawny nurse shark is restricted to is heavily fished, with the species being captured in demersal trawls, floating and fixed bottom gill nets and baited hooks across most of its range outside Australia (1). The flesh is sold for human consumption, with the fins making their way into the oriental sharkfin market. The species’ liver may also be processed for vitamins and oil, the offal processed for fishmeal, and the hide potentially for leather (2). The exact impact fishing is having on population numbers is unknown, but there are reports of local extinctions in waters around India and Thailand. Certainly, the shark’s narrow habitat range, apparently limited dispersion and low reproductive turnover make it highly vulnerable to the effects of over-fishing. Fortunately, this shark is still abundant in Australian waters, where it is captured only in very small numbers in gillnets and meshing (1).
There are currently no conservation measures targeting this species (1).
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- Demersal: fish that live on or near the ocean bottom. They are often called benthic fish, groundfish, or bottom fish.
- Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
- Nocturnal: active at night.
- Ovovivipary: method of reproduction whereby the egg shell is weakly formed and young hatch inside the female; they are nourished by their yolk sac and then ‘born’ live.
- Pectoral fins: in fish, the pair of fins that are found one on each side of the body just behind the gills. They are generally used for balancing and braking.
IUCN Red List (December, 2009)