Nurse sharks (Ginglymostoma cirratum) are known for their docile nature, leading most experts to consider them non-aggressive toward humans. These bottom-dwelling species spend the majority of their time resting on the seabed, minimizing interaction with people. While large, reaching an average length of 7.5 to 9.75 feet and weighing up to 330 pounds, their anatomy and behavior do not align with a predatory threat to humans. Documented bites are nearly always linked to specific circumstances rather than true attacks.
Understanding Nurse Shark Temperament
The nurse shark’s biology and lifestyle contribute to its reputation as a slow-moving, placid animal. This species is largely nocturnal, hunting for food along the ocean floor at night. During the day, nurse sharks commonly rest in groups of up to 40 individuals, often piled together in coral crevices or under ledges. This sedentary behavior makes them appear sluggish.
The shark’s physical adaptations are specialized for its diet of small, bottom-dwelling organisms. Nurse sharks primarily feed on crustaceans, mollusks like conchs and octopuses, and small fish. They possess a small mouth and a powerful, bellows-like pharynx, allowing them to use suction to inhale prey quickly. Their small, serrated teeth are designed for crushing the hard shells of crabs and clams, not for tearing the flesh of large animals.
Analyzing Bites Versus Predatory Attacks
When a nurse shark interacts aggressively with a human, it is nearly always a defensive reaction rather than a true predatory attack. A predatory attack is driven by a feeding instinct, but a defensive bite is a response to feeling provoked, threatened, or disturbed. Nearly all documented incidents are categorized as provoked, meaning the human initiated the interaction by touching, cornering, or harassing the animal.
The International Shark Attack File recorded 51 provoked bites and only five unprovoked bites globally before 2022. Provocation often involves divers or swimmers attempting to grab the shark’s tail, stepping on a resting shark, or trying to feed it by hand. When biting, a nurse shark may clamp down strongly and hold on, which can result in significant tissue damage due to their powerful jaws and crushing teeth. However, the injury is a defensive measure to escape a perceived threat, not a feeding bite intended to consume.
Safe Interaction Guidelines
The best defense against a nurse shark bite is to maintain a respectful distance and avoid disturbing the animal in its natural habitat. Since these sharks are most often encountered resting during the day, they are vulnerable to disturbance.
Divers and snorkelers should never attempt to touch, ride, or grab any part of the shark, as this is the most common trigger for a defensive bite. Avoid swimming near or harassing nurse sharks resting in caves or under ledges, as cornering them can cause them to feel trapped and lash out. Additionally, refrain from feeding nurse sharks by hand, as this teaches them to associate humans with food and can lead to accidental bites.