The Nervous Shark is a species of requiem shark, family Carcharhinidae, so named because of its timid behavior with regard to humans. The harmless nervous shark is caught incidentally by coastal gillnet fisheries and perhaps also by line and trawl fisheries. The International Union for Conservation of Nature (IUCN) lacks sufficient data to assess the conservation status of this species except in Australian waters, where its population seems healthy and has been listed under Least Concern.
Description[]
The nervous shark has a rather stout, spindle-shaped body and a short, broadly rounded snout. The anterior margin of each nostril is extended into a slender nipple-shaped lobe. The moderately large eyes are horizontally oval in shape and equipped with nictitating membranes. The mouth lacks conspicuous furrows at the corners and contains 25–30 upper and 23–28 lower tooth rows. The upper teeth are narrow and angled, with coarsely serrated edges. The lower teeth are more slender and upright in shape, and have finer serrations. The five pairs of gill slits are medium in length.
The pectoral fins are moderately long, narrow, and pointed. The first dorsal fin originates over the free rear tips of the pectoral fins; it is large and falcate (sickle-shaped) with a pointed apex. The second dorsal fin is positioned opposite the anal fin and is relatively large and high. There is no ridge between the dorsal fins. A crescent-shaped notch is present on the caudal peduncle just before the upper caudal fin origin. The caudal fin is asymmetrical, with a strong lower lobe and a longer upper lobe with a ventral notch near the tip. The dermal denticles are overlapping and bear three horizontal ridges (five in larger individuals) leading to marginal teeth. This species is bronze to gray above and white below, with a white stripe on the flank. A thin black line runs along the leading margins of the dorsal fins, pectoral fins, and the upper caudal fin lobe, as well as the caudal fin trailing margin; the lower caudal fin lobe and sometimes the pectoral fins are also tipped in black. The nervous shark typically reaches 1.0–1.3 m (3.3–4.3 ft) in length and may grow up to 1.5 m (4.9 ft) long. Females attain larger sizes than males.
Habitat[]
This species generally inhabits shallow inshore waters, to a depth of at least 45 m (148 ft). It seems to particularly favor mangrove-lined areas with sandy-muddy bottoms and avoids areas with dense seagrass cover.
Food[]
The diet of the nervous shark consists mainly of small teleost fishes (including silversides, smelt-whitings, wrasses, and grunters). Crustaceans (including prawns, crabs, and mantis shrimps) and molluscs (predominantly cephalopods, but also bivalves and gastropods) constitute secondary food sources. This shark is also known to occasionally prey on the semiaquatic snakes Cerberus rynchops and Fordonia leucobalia.