The nurse shark (Ginglymostoma cirratum) is a common, slow-moving species often encountered by divers in tropical waters. This bottom-dwelling shark belongs to the carpet shark order, Orectolobiformes. Unlike more active relatives, the nurse shark is sedentary, spending much of its day resting on the substrate. Its scientific name refers to its unique facial features, translating roughly to “hinged mouth with curled ringlets.”
Distinct Physical Characteristics
Adult nurse sharks are typically light tan to dark brown. Their bodies are stout, featuring a broad head with small eyes positioned far forward. The mouth is notably small and positioned well in front of the eyes, giving the head a rounded appearance.
A distinctive pair of fleshy sensory appendages, called barbels, hang near the nostrils and extend toward the mouth. These barbels function as chemosensors, helping the shark locate prey hidden in the sand or crevices. They possess two rounded dorsal fins, lacking the spines found in some other shark species, with the first fin being larger than the second.
The shark’s powerful, elongated tail fin, or caudal fin, makes up more than one-quarter of its total body length and lacks a distinct lower lobe. This long, muscular tail helps propel the shark when it is actively swimming. Adult nurse sharks average between 7.5 and 8 feet in length, though some individuals grow up to 14 feet.
Habitat, Range, and Temperament
The nurse shark inhabits the warm, coastal waters of the tropical and subtropical Atlantic and Eastern Pacific Oceans. Their geographic range extends in the Western Atlantic from Brazil up to North Carolina, including the Caribbean Sea and the Gulf of Mexico. They prefer shallow environments, such as coral reefs, sand flats, and mangrove edges, though adults can be found in depths up to 75 meters during the day.
These sharks are primarily nocturnal, spending daylight hours resting motionless on the bottom, often tucked under rocky ledges or in caves. Nurse sharks are one of the few shark species that can actively pump water over their gills while stationary, allowing them to remain still. They frequently rest in groups, sometimes piling on top of one another in a single sheltered location.
The species is known for its mild and sluggish temperament. Nurse sharks are not considered aggressive toward humans, and bites are uncommon. Bites typically occur only when a person provokes, handles, or accidentally steps on a resting individual. A provoked bite can be powerful and capable of inflicting a serious injury.
Specialized Feeding Strategy
The nurse shark is an opportunistic bottom feeder, primarily consuming benthic invertebrates and small fish. They often forage at night, slowly moving along the seafloor, sometimes using their muscular pectoral fins to “clamber” across the substrate. Their diet includes crustaceans like lobsters and crabs, mollusks such as octopuses and clams, and small fish and stingrays.
The feeding mechanism of the nurse shark is highly specialized, relying on powerful suction rather than a large bite. They are obligate suction feeders, meaning they capture prey by rapidly expanding their pharynx to create a strong vacuum. This action is so forceful that it has been measured as one of the highest suction pressures recorded for any aquatic vertebrate.
The small, sub-terminal mouth and specialized anatomy, including a loosely connected hyoid arch, facilitate this rapid, high-pressure intake of water and food. Suction feeding is most effective at very close range, constraining the shark’s foraging to stalking or ambushing prey.
Reproduction and Life Cycle
Nurse sharks reproduce through ovoviviparity, where the eggs hatch internally within the mother’s uterus. The developing embryos are nourished by a yolk sac inside the egg case, with no direct placental connection to the mother.
The reproductive cycle is biennial. Mating usually occurs in the summer months, followed by a gestation period that lasts between five and six months. Females give birth to litters that commonly range from 20 to 30 pups, with each newborn measuring approximately 10 to 12 inches in length.
Growth is slow, with males reaching sexual maturity between 10 and 15 years of age and females between 15 and 20 years. Juvenile nurse sharks often use shallow, protected areas like mangrove swamps and sea grass beds as nurseries before moving to deeper reefs as adults. Globally, the nurse shark is listed as Vulnerable by the IUCN, although populations in some regions, such as the United States and the Bahamas, are considered to be of Least Concern.