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Author: (Lesson, 1830)

Field Marks:
Moderately long barbels, nasoral grooves present but no perinasal grooves, mouth well in front of eyes, eyes lateral, spiracles minute, precaudal tail shorter than head and body, two spineless, angular dorsal fins and an anal fin, first dorsal fin much larger than second dorsal and anal fins, first dorsal base over pelvic bases, pectoral fins falcate, caudal fin moderately long, over 1/4 of total length, colour brown, from tan to dark grey-brown according to habitat, and slowly changeable by the individual.

Diagnostic Features:
Teeth more or less compressed in sides of jaws, forming imbricated series. Dorsal, pectoral, and anal fins apically angular, pectoral fins narrow and falcate.

Geographical Distribution:
Indo-West and Central Pacific: South Africa, Mauritius, Scychelles and Madagascar to Red Sea, India, Malaysia, Indonesia, Singapore, Thailand, Viet Nam, China, Papua New Guinea, Australia (Queensland), New Caledonia, New Ireland, Samoa, Palau, Marshall Islands, Tahiti.

Habitat and Biology:
A large, tropical inshore shark of the continental and insular shelves, commonly in the intertidal in water scarcely able to cover it and from the surf line down to a few metres depth, but ranging down to at least 70 m. It occurs on or near the bottom in lagoons or along the outer edges of coral and rocky reefs, sandy areas near reefs and off sandy beaches. It prefers sheltered areas in crevices and caves on reefs but often occurs in more exposed areas in a depression or crevice. The tawny shark is primarily nocturnal, resting in the daytime in shelters butprowling slowly about around reefs at night, although a few individuals may be active in the day. They are gregarious and form resting aggregations of two to a half-dozen or more in shelters, and are often seen piled inertly across or on top of one another. When resting, they are extremely sluggish.

Reproduction ovoviviparous, described as an oviparous or post-oviparous shark that retains the egg-cases until they hatch and the young are born. Number of young at least four per uterus.

Food of this shark includes corals, crabs, lobsters and other crustaceans, octopuses, squids and probably other cephalopods, sea urchins, and reef fishes (including surgeonfishes and siganids). While foraging the tawny shark moves along the bottom and explores depressions, holes and crevices in reefs. When it detects prey it places its small mouth very close to the victim, and uses its large pharynx as a powerful suction pump to rapidly inhale in reef organisms that may be out of reach of its teeth. A few large individuals dissected by the writer had quantities of small, active reef fishes in their stomachs, presumably sucked in by the sharks as the prey fishes lay inert in shelters or on the bottom at night. Individuals caught by fishermen may reverse this sucking action, and blast streams of water out of their mouths into the faces of their captors; they are said to make a grunting sound between streams.

This has been described as a much more docile species than its close relative, Ginglymostoma cirratum, and apparently usually allows humans to touch and play with it without biting. However, there are a few non-fatal attack records of these sharks biting their tormentors, and clamping tightly onto them. Because of its size and strength, the tawny shark should be regarded as potentially dangerous and treated with respect.

This is a tough, hardy shark that readily survives in captivity.

Size:
Maximum total length about 314 to 320 cm; though most individuals are smaller; an adult male was 250 cm long and two adults females, from 230 to 290 cm; size at birth about 40 cm.

Interest to Fisheries:
Common in areas where it occurs, and caught inshore by fishermen in Pakistan, India, and Thailand, and probably elsewhere. It is utilized fresh and dried salted for human food, its liver is rendered for oil and vitamins, its fins are used in the oriental sharkfin trade, and offal is processed into fishmeal. Its thick, armor-like hide is potentially valuable for leather. Off Queensland, Australia, it has been fished as a big-game shark, and large individuals are prized as powerful fighters.

Remarks:
I tentatively include Nebrius concolor and its synonyms in synonymy of N. ferrugineus. Normally these species are retained and often placed in different genera, with N. ferrutineus being usually placed in Ginglymostoma and concolor in Nebrius. However, the dentitional differences used to separate the two species (as in Garman, 1913, and Fowler, 1941: more compressed, more low-cusped teeth in concolor and less compressed, more high-cusped teeth in ferrugineus) may be due to growth changes in the teeth of a single species (ontogenetic heterodonty). At least in the material of Nebrius examined from the Gulf of Thailand and elsewhere, larger specimens over 2 m long have teeth of the ferrugineus type, while specimens about a meter long or less have teeth of the concolor type. Teeth of a specimen 1.8 m long pictured by Bass, d'Aubrey and Kistnasamy (1975b) are roughly intermediate. Growth changes apparently include increase in size of cusps relative to cusplets, shortening and broadening of the labial flange, and thickening and broadening of the teeth relative to their height.

Type material:
Holotype: ?. Type Locality: ? Mentioned as occurring at New Ireland and Waigiou, south Pacific.

Tawny nurse shark (Nebrius ferrugineus)