Nurse sharks are a type of shark known for their calm disposition. These bottom-dwelling creatures typically spend their days resting, often in groups, before becoming more active under the cover of night. They thrive in warm, shallow marine environments, making them a common sight for divers.
Defining Nurse Sharks
Nurse sharks, scientifically known as Ginglymostoma cirratum, possess distinct physical characteristics. They typically exhibit a yellowish-tan to dark brown coloration; juveniles may have small dark spots that fade with age. Adults average 2.3 to 2.7 meters (7.5 to 9 feet) in length and can weigh over 90 kilograms (200 pounds), with females often slightly larger than males.
Their appearance is characterized by a flattened head and a broad, rounded snout. Two prominent, fleshy barbels between their nostrils are sensory organs used for detecting prey. Their skin is smooth to the touch, unlike the rough texture of many other shark species.
Habitat and Behavior
Nurse sharks are commonly found in the warm, shallow waters of the tropical and subtropical Atlantic and Eastern Pacific oceans. They prefer habitats such as coral reefs, sandy bottoms, and mangrove channels, often resting in caves or under ledges during the day. These sharks are primarily nocturnal, spending daylight hours in a sedentary state on the seafloor. They can often be seen lying in groups, sometimes piled upon one another, with up to 40 individuals. Unlike some other shark species, nurse sharks do not need to constantly swim to breathe; they can pump water over their gills while stationary.
Diet and Feeding Habits
Nurse sharks are opportunistic bottom feeders with a diverse diet. Their prey primarily consists of crustaceans like crabs and lobsters, mollusks such as clams and octopi, small fish, and sea urchins. They employ a unique suction-feeding method, using their small mouths and powerful throat muscles to vacuum up food. This allows them to extract prey from crevices within reefs or from the ocean floor. They can even dismember prey with the intensity of their suction, and their serrated teeth help crush hard-shelled items.
Interaction with Humans
Nurse sharks are generally known for their docile nature and are not typically considered dangerous to humans. They are often encountered by divers and snorkelers without incident. However, bites can occur if the shark is provoked or disturbed, with common scenarios including stepping on them, grabbing their tails, or attempting to feed them by hand. While nurse shark bites are not usually fatal, their strong jaws and small, serrated teeth can inflict significant tissue damage. Unprovoked attacks are extremely rare, with records showing a considerably higher number of provoked incidents.
Conservation Status
The nurse shark (Ginglymostoma cirratum) is currently classified as “Vulnerable” on the IUCN Red List of Threatened Species. Threats to nurse shark populations include coastal fisheries, where they are sometimes caught as bycatch, and habitat degradation. In some regions, they are still targeted for their fins, meat, or skin, or are considered a nuisance animal by local fishermen.