Nurse sharks, scientifically known as Ginglymostoma cirratum, are a species of bottom-dwelling shark commonly found in the warm, shallow, tropical, and subtropical coastal waters of the Atlantic and Eastern Pacific Oceans. These sharks typically exhibit a yellowish-tan to dark brown coloration and possess a broad, rounded head with two distinct barbels near their nostrils, which function as sensory organs. Adult nurse sharks generally range from 2.3 to 2.7 meters (7.5 to 9 feet) in length and can weigh between 68 to 136 kilograms (150 to 300 pounds), though some individuals may exceed 3 meters (10 feet).
Assessing Their Threat Level
Nurse sharks are widely considered docile and non-aggressive towards humans. Bites are infrequent and almost exclusively occur when the shark is provoked or disturbed, such as by divers grabbing their tails, accidentally stepping on them, or attempting to feed them.
According to reports from the International Shark Attack File, there were approximately 51 provoked bites and 5 unprovoked bites by nurse sharks globally before 2022, with no recorded fatalities. Their teeth are small, serrated, and designed for crushing the shells of bottom-dwelling prey, rather than for tearing flesh. While a bite can cause injury due to their strong jaws and ability to suction onto objects, they are not typically severe.
Understanding Their Natural Behavior
Nurse sharks are nocturnal predators, meaning they are most active at night when searching for food. During daylight hours, they commonly rest motionless on the seafloor or seek shelter in caves and crevices. They are often observed resting in groups, sometimes piling on top of one another, with aggregations of up to 40 individuals documented.
These sharks are slow-moving and can use their muscular pectoral fins to “clamber” or “walk” across the seabed. Their diet primarily consists of bottom-dwelling organisms such as crustaceans like crabs, shrimp, and lobsters, as well as mollusks including clams, conchs, squid, and octopi. They also consume small fish, such as lizardfish and rays. Nurse sharks are skilled suction feeders, capable of generating powerful suction forces to extract prey from tight spaces or shells. Unlike many other shark species, they can breathe while remaining stationary by actively pumping water over their gills.
Safe Encounters
Interacting with nurse sharks in their natural habitat requires respect for their space and behaviors. Maintaining a respectful distance is important to avoid disturbing them. It is advised to avoid touching or attempting to provoke them, as this is the primary cause of bites.
Feeding nurse sharks is not recommended, as it can disrupt their natural hunting instincts and may lead to accidental bites. When encountering a nurse shark, moving calmly and slowly is beneficial. If a shark exhibits warning behaviors, such as arching its back or making quick head movements, retreating immediately is a prudent action. Following guidance from marine professionals or dive instructors can further ensure a safe experience for both humans and the sharks.