Nurse Shark Facts: Description, Habitat, and Behavior

The nurse shark (Ginglymostoma cirratum) is a type of carpet shark. This slow-moving bottom dweller is known for its docile nature and adaptation to captivity. It is a different species from the grey nurse shark (one of the names for the sand tiger shark, Carcharias taurus) and the tawny nurse shark (Nebrius ferrugineus, another type of carpet shark).

Description

The shark's genus name Ginglymostoma means "hinged mouth" in Greek, while the species name cirratum means "curled ringlets" in Latin. The nurse shark's mouth has a puckered appearance and opens much like a hinged box. The mouth is lined with rows of tiny backward-curled teeth.

An adult nurse shark is solid brown, with smooth skin, a broad head, elongated caudal fin, and rounded dorsal and pectoral fins. Juveniles are spotted, but they lose the pattern with age. There are numerous reports of nurse sharks occurring in unusual colors, including milky white and bright yellow. Scientists have discovered this species of shark is able to change its color in respond to light.

The largest documented nurse shark was 3.08 m (10.1 ft) long. A large adult may weigh about 90 kg (200 lb).

Distribution and Habitat

Nurse sharks occur in warm tropical and subtropical waters off coasts of the Eastern and Western Atlantic and the Eastern Pacific. They are bottom-dwelling fish, living at a depth appropriate to their size. Juveniles prefer shallow reefs, mangrove islands, and seagrass beds. Larger adults live in deeper water, taking refuge under rocky ledges or reef shelves during daytime. The species is not found in cooler deep water.

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Shark Facts: Habitat, Behavior, Diet

By Jennifer Kennedy

Diet

During the night, nurse sharks leave their group, venturing out for solo feeding forays. They are opportunistic predators that disturb bottom sediment to uncover prey, which they capture using suction. When captured prey is too large for a shark's mouth, the fish violently shakes its catch to tear it or uses a suck-and-spit technique to break it apart. Once captured, prey is crushed by the shark's strong jaws and ground by its serrated teeth.

Usually, nurse sharks feed upon invertebrates and small fish. Where nurse sharks and alligators are found together, the two species attack and eat each other. Nurse sharks have few predators, but other large sharks do occasionally feed on them.

Behavior

Nurse sharks have a low metabolism and generally expend minimal energy. While most sharks need to move to breathe, nurse sharks can rest motionless on the sea floor. They face against the current, allowing the water to flow into their mouths and across their gills.

In the daytime, nurse sharks rest on the sea bottom or hidden under ledges in groups as large as 40 individuals. Within the group, they appear to snuggle and cuddle with each other. Scientists believe this may be an example of social behavior. Nurse sharks are most active at night, when they hunt.

Reproduction

Male nurse sharks reach sexual maturity between 10 and 15 years of age, while females become mature between 15 and 20 years of age. As in some other shark species, the male bites the female to hold her for mating. Since many males may attempt to mate with a female, it's not uncommon for a female nurse shark to bear numerous scars.

The species is ovoviviparous or live-bearing, so eggs develop in an egg case within the female until birth. Gestation typically lasts 5 to 6 months, with the female giving birth in June or July to about 30 pups. It is not uncommon for the pups to cannibalize each other. After giving birth, it takes another 18 months before the female produces enough eggs to breed again. Nurse sharks live 25 years in captivity, although they may reach 35 years of age in the wild.

Nurse Sharks and Humans

Nurse sharks adapt well to captivity and are an important species for research, primarily in the area of shark physiology. The species is fished for food and leather. Because of their docile nature, nurse sharks are popular with divers and ecotourists. However, they are the responsible for the fourth highest incidence of human shark bites. The sharks will bite if threatened or injured.

Conservation Status

The IUCN List of Threatened Species has not addressed the conservation status of nurse sharks, due to insufficient data. Generally, experts consider the species to be of least concern off the coasts of the United States and Bahamas. However, populations are vulnerable and declining elsewhere in their range. The sharks face pressure from their close proximity to human populations and are threatened by pollution, overfishing, and habitat destruction.

Sources

• Castro, J. I. (2000). "The biology of the nurse shark, Ginglymostoma cirratum, off the Florida east coast and the Bahama Islands)". Environmental Biology of Fishes. 58: 1–22. doi:10.1023/A:1007698017645
• Compagno, L.J.V. (1984). Sharks of the World: An annotated and illustrated catalogue of shark species known to date. Food and Agriculture Organization of the United Nations. pp. 205–207, 555–561, 588.
• Motta, P. J., Hueter, R. E., Tricas, T. C., Summers, A. P., Huber, D. R., Lowry, D., Mara, K. R., Matott, M. P., Whitenack, L. B., Wintzer, A.P. (2008). "Functional morphology of the feeding apparatus, feeding constraints, and suction performance in the nurse shark Ginglymostoma cirratum". Journal of Morphology. 269: 1041–1055. doi:10.1002/jmor.10626
• Nifong, James C.; Lowers, Russell H. (2017). "Reciprocal Intraguild Predation between Alligator mississippiensis (American Alligator) and Elasmobranchii in the Southeastern United States". Southeastern Naturalist. 16 (3): 383–396. doi:10.1656/058.016.0306
• Rosa, R.S.; Castro, A.L.F.; Furtado, M.; Monzini, J. & Grubbs, R.D. (2006). "Ginglymostoma cirratum". The IUCN Red List of Threatened Species. IUCN. 2006: e.T60223A12325895.