The Nervous shark (Carcharhinus cautus) is a species of requiem shark, and part of the family Carcharhinidae. It can be found in shallow coasts round Papua New Guinea, the Solomon Islands and northern Australia. It is extremely anxious, skittish and shy around humans.
Family: Carcharhinidae – Requiem sharks
Genus: Carcharhinus
Species: cautus
Phylum– Chordata
Class– Chondrichthyles
Subclass– Elasmobranchii
Common Name– Ground Sharks
Family– Carcharhinidae
Common Name– Requiem Sharks
Genus– Carcharhinus
Species– cautus
Status: IUCN Red List DATA DEFICIENT
Average Size and Length: The Nervous shark typically reaches 3.3–4.3 feet in length and may grow up to 4.9 feet long. Females grow larger than male Nervous sharks.
Teeth and Jaw: The Nervous shark has 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.
Head: It has a short and broad rounded snout.
Denticles: The dermal denticles are overlapping and have t3 horizontal ridges (5 in larger sharks) leading to marginal teeth.
Tail: 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.
Demographic, Distribution, Habitat, Environment and Range: 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.
The Nervous shark is one of the most common sharks in Darwin Harbor, the Gulf of Carpentaria, and Shark Bay. It prefers shallow inshore waters, to a depth of at least 148 feet. It seems to predominantly favor mangrove-lined areas with sandy-muddy bottoms and avoids areas with dense seagrass cover.
Diet: The Nervous shark mainly eats small teleost fishes like silversides, smelt-whiting’s, wrasses, and grunters. It also eats crustaceans like prawns, crabs, and mantis shrimps, and mollusks; predominantly cephalopods but also bivalves and gastropods.
The Nervous shark is also known to occasionally prey on the semiaquatic snakes Cerberus rynchops and Fordonia leucobalia.
Aesthetic Identification: The Nervous shark has a spindle-shaped body and is quite stout. It has five pairs of gill slits are medium in length. The Nervous shark is bronze to gray above and counter-shaded white below, with a white stripe on the flank.
The pectoral fins are somewhat long, narrow, and pointed. The first dorsal fin originates over the free rear tips of the pectoral fins; it is large and with a pointed apex. The second dorsal fin is positioned opposite the anal fin and is large and high.
There is no ridge between the dorsal fins.
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.
Biology and Reproduction: A known parasite of the nervous shark is the myxosporean, Kudoa carcharhini.
The Nervous shark is viviparous.
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 8 to 9 months. In Shark Bay, mating occurs from late October to early November and birthing occurs around the same time the following year, following a gestation period of 11 months; this slower development likely reflects the cooler temperatures of Shark Bay.
Females produce litters on an annual cycle in Darwin Harbor and on a biennial cycle in Shark Bay. The litter size ranges from 1 to 6 and is not correlated with the size of the female. The newborns are born from 14–16 inches long, and are birthed in shallow nursery areas such as Herald Bight in Shark Bay.
Both males and females mature sexually at around 33 to 40 inches depending on the location. They are mature at around 4 years in age for males and 6 years for females. The maximum lifespan for a female is 16 years and 12 for males.
Behavioral Traits, Sensing and Intelligence: The male bites at the sides of the female prior to mating.
Nervous Shark Future and Conservation: It is occasionally marketed for food. This species is susceptible to being caught incidentally in coastal gillnets. It may also be caught on line gear and in prawn trawls.
Nervous Shark Recorded Attacks on Humans: There is no threat to humans from the Nervous shark. They are shy and difficult to approach; the Nervous shark is harmless to humans.