Nervous Shark

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. …

The nervous shark is found over continental and insular shelves off northern Australia from Shark Bay in the west to Moreton Bay in the east, as well as off Papua New Guinea and around the Solomon Islands. It is among the most common sharks in Darwin Harbor, the Gulf of Carpentaria, and Shark Bay. 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.

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. A known parasite of the nervous shark is the myxosporean Kudoa carcharhini. Like other requiem sharks, the nervous shark is viviparous: once the embryos exhaust their initial supply of yolk, they are provisioned by the mother through a placental connection formed from the depleted yolk sac. Adult females have a single functional ovary, on the right, and two functional uteruses. The male bites at the sides of the female as a prelude to mating. After mating, the female stores the sperm for approximately four weeks prior to fertilization. In Darwin Harbor, mating occurs from January to March and birthing occurs in October and November following a gestation period of eight to nine months. …