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. The tawny nurse shark is uniformly grey to tan-brown on its upper surfaces, paling slightly on the belly. Juveniles can be distinguished from adults by the presence of small dark spots on the skin. This large shark has a broad, flattened head with a squarish snout and tiny eyes. 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.
Tawny nurse shark habitat
It occurs on or near the bottom in lagoons, in channels or along outer edges of coral and rocky reefs, in areas with seagrass and sand on reefs, sandy areas near reef and off sandy beaches. It prefers areas in crevices and caves. Young prefer crevices in shallow lagoons but adults are more wide ranging.
Life History: Ovoviviparous (aplacental viviparity) with uterine cannibalism in the form of oophagy. Pregnant females from Okinawa had one or two foetuses per uterus (297 to 595 mm) with the yolk sac reabsorbed and a greatly expanded stomach filled with yolky material in the larger fetuses and also had egg cases in the uterus (Teshima et al. 1995). It appears as though this species practices oophagy on relatively large, cased nutritive eggs (unlike lamnoids which have very small nutritive eggs) and is the first orectoloboid known to have uterine cannibalism. It is not known if the foetuses eat each other (adelphophagy) as with the grey nurse shark (Carcharias taurus).
Reproductive periodicity: Unknown Size at birth: 40 to 80 cm total length (TL) Average litter size: At least four per uterus suggested from egg cases, but the large size differences between foetuses in a litter suggests the litters are smaller, possible only one per female (Compagno 2001). Size male maturity: 250 cm TL Size female maturity: 230 to 290 cm TL Max size: to at least 320 cm TL Growth rates: Unknown
Tawny nurse shark threats
Threats within Australia are likely to be minimal, there are no target fisheries, although it is taken in inshore fisheries throughout much of the rest of its range.
In the Gulf of Thailand, it was historically more abundant and it may have been adversely affected by the use of explosives and poisons on reefs in the Indian Ocean and western Pacific, particularly Indonesia and the Philippines (Compagno 2001). Nebrius ferrugineus often form small aggregations during the day and have a limited home range, with individuals returning to the same area every day after foraging. This behaviour together with small litter size, large size at maturity and inshore habitat suggest that it is vulnerable to local population depletion in areas of heavy fishing pressure. Furthermore, its docility and habit of resting in caves and crevices during the day make it susceptible to capture and harassment by divers, and reef destruction.