I got to experience my first nurse shark encounter during a night dive while part of Mermaid Kat’s Mermaid Week Maldives 2021. Nurse sharks are found off the coast in warm tropical and subtropical waters and are popular with divers and ecotourists.
Adults are about 3 meters or 10 feet long, weighing 90 kilograms or 200 pounds. They are a solid brown but can change their color in response to light and some have appeared to be a bright yellow or a milky white. Young nurse sharks are spotted but they lose their spots with age. Nurse sharks have rounded dorsals, a broad head, smooth skin, and barbells. Barbells are located below their nostrils and assist the sharks in locating prey by helping provide a sense of touch.
Speaking of prey, they are opportunistic predators that rummage around the sediment on the bottom of the seafloor for invertebrates and small fish. They hunt at night, so it is easier for them to capture prey that is mostly awake during the daytime. Nurse sharks favor shrimps, crabs, bivalves, and other similar creatures. They capture their prey using suctions - they can even suck a queen conch straight out of its shell! If the prey is too big, they’ll violently shake it to tear it or use a suck and spit method to break it apart. Once in it’s puckered mouth, which opens like a hinged box and is lined by rows of tiny backward curled teeth, the shark then crushes its prey with it’s strong jaws and grounds it with its serrated teeth. When in the same environment as alligators, they have been known to attack and eat each other. Large sharks will also occasionally feed on nurse sharks.
Nurse sharks are not related to grey nurse sharks, which is another name for a Sand Tiger Shark, and they aren’t the same species as tawny nurse sharks, which are also part of the carpet shark family. The origin of the name “nurse shark” is a bit unclear, but there are three solid guesses as to how it came about. The first is that when it is sucking its prey it sounds similar to a nursing baby. Another thinks it comes from the archaic word “nusse” which means cat shark, and the third thinks it comes from the Old-English word “hurse” which means sea-floor shark.
The meaning of their scientific name is a bit more clear. Ginglymostoma cirratum is a mix of Greek and Latin and means “curled, hinged mouth”, which makes sense with what we just learned about their mouths and how they eat. Ginglymostoma is Greek for hinged mouth while cirratum is Latin for curled ringlets. Nurse sharks are a type of carpet shark and are best known for their docile nature, being a slow-moving bottom dweller, and their ability to adapt to captivity. In captivity, they have been known to be trained to work with a handler.
Nurse sharks can live 25 years in captivity and 35 years in the wild. They have a low metabolism which leaves them with minimal energy. During the day, they rest facing against the current on the seafloor so that water can flow into their mouth and across their gills while they lay motionless in groups of up to 40 nurse sharks. They aren’t found in deep, cold water. Adults tend to rest on rocky ledges of reef shelves while juveniles stay in shallower reefs, mangrove islands, and seagrass beds. Nurse sharks are most active at night when they hunt.
They are not listed on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species due to insufficient data, as the global population is unknown at this time. However it is thought that the populations off the coast of the United States and Bahamas are of least concern, while elsewhere in the world they might be vulnerable or declining. Like all sharks, they are threatened by pollution, overfishing, and habitat destruction. They are fished for food and for leather. Additionally, nurse sharks are very important for research, especially when it comes to shark physiology.
Nurse sharks are one of 39 shark species covered in the Exclusive Economic Zone, a plan by the US National Marine Fisheries Service that hopes to “stabilize shark populations through reduction of commercial and recreational fishing procedures via licensing and quotas” in the Atlantic and Gulf of Mexico, from state waters up to 200 miles offshore.
Despite their docile nature, nurse sharks are statistically the 4th highest number of human shark attacks. They will bite if threatened or injured and every attack from a nurse shark on record was due to the shark being provoked. While they rest motionless during the day, it gives people a false sense of security, leading them to poke, prod, and pull on the wild sharks. The shark will then give a defensive bite, which is then recorded as a shark attack. As always, look with your eyes, not your hands, and leave the sharks alone.