The nurse shark (Ginglymostoma cirratum) is a slow-moving, bottom-dwelling species that contrasts sharply with fast-swimming pelagic sharks. It spends much of its life resting on the seafloor, navigating the complex environments of tropical reefs rather than the open ocean. Adults are large, typically reaching lengths between 7.5 and 9.75 feet and weighing 200 to 330 pounds. This species is often called the cat shark, possibly due to the whisker-like sensory organs, called barbels, that hang from its snout.
Where Nurse Sharks Live
Nurse sharks are widely distributed across the warm, shallow waters of the world’s oceans, showing a strong preference for tropical and subtropical zones. Their range extends across the Western Atlantic, from Rhode Island down to southern Brazil, encompassing the Gulf of Mexico and the Caribbean Sea. They are also found in the Eastern Atlantic, near the Cape Verde Islands and along the coast of West Africa, as well as in the Eastern Pacific, from Baja California to Peru.
These sharks are non-migratory and exhibit high site fidelity, often returning to the same specific resting spots repeatedly. Their preferred habitats include complex structures such as coral reefs, mangrove keys, rocky areas, and sand or seagrass flats. They are bottom dwellers frequently observed in very shallow waters, sometimes less than a meter deep, but they can be found down to depths of about 75 meters during the day.
The nurse shark’s ability to remain stationary without swimming is a major factor in its habitat preference. Unlike many sharks that must swim continuously to force water over their gills, the nurse shark uses a method called buccal pumping to draw water over its gills while resting. This adaptation allows them to settle on the bottom or rest within caves and crevices for extended periods. This ability also contributes to their tolerance for environments with lower dissolved oxygen levels compared to other shark species.
What Nurse Sharks Eat
The diet of the nurse shark consists primarily of small, bottom-dwelling animals, reflecting its life spent near the seafloor. They are nocturnal hunters, actively foraging at night when many of their prey items are slow-moving or resting. Their main food sources include a variety of invertebrates such as crabs, shrimp, spiny lobsters, sea urchins, and shelled mollusks like conchs and clams. They also consume small reef fish that are often resting at night.
The nurse shark employs a specialized feeding technique known as suction feeding to capture prey. Using a muscular pharynx, they rapidly expand their buccal cavity, which creates a powerful vacuum that sucks prey directly into their mouth. This vacuum force is so intense that it allows them to pull prey items out of small holes in the reef or even extract snails from heavy shells. Their small, downward-facing mouth is ideally suited for foraging along the contours of the ocean floor.
The small barbels that protrude near their nostrils are used to sense the presence of prey hidden in the sand or crevices. These whisker-like organs help them locate food by touch and chemoreception before the suction mechanism is deployed. Algae and coral fragments have sometimes been found in their stomach contents, likely ingested accidentally as the shark forcibly vacuumed its primary prey from the reef structure.
How Nurse Sharks Behave
A notable aspect of their social behavior is their gregariousness, especially while resting. Nurse sharks frequently aggregate in groups, sometimes numbering up to 40 individuals, lying closely together or even piled on top of one another. This grouping behavior is related to their strong loyalty to specific daytime resting sites, which they return to consistently after nocturnal foraging.
Reproduction is characterized by an ovoviviparous strategy, meaning the embryos develop inside egg cases within the mother’s uterus, sustained by a yolk sac. Mating rituals, which often occur in the shallow waters off Florida in late spring and summer, are among the most documented for any shark species. Courtship involves one or more males surrounding a female, with the male biting and holding onto the female’s pectoral fin to position her for copulation.
The mating process can be vigorous, with the female often sustaining noticeable bite marks and bruises from the male’s grasp. Females typically have a biennial reproductive cycle and give birth to a litter of between 21 and 28 pups after a gestation period of five to six months. Despite their generally placid nature, nurse sharks will defend themselves if provoked and have been known to bite humans who accidentally step on them or attempt to grab them.