While on a short boating trip to South Bimini Island in the Bahamas last week, I paid a visit to the marine field station there, known as the “Shark Lab.” I got a close look at one of the species of sharks that they are studying: the nurse shark.Adorned with a pair of catfish-like barbels, small eyes and not-very-prominent dentition, the nurse shark (Ginglymostoma cirratum) must rank as one of the most unintimidating-looking sharks in the world. They are not aggressive, and due to their generally docile nature they have a reputation for being “harmless.” Most “bad encounters” with this species are the result of people grabbing or poking them, causing the shark to clamp their small but powerful “vice-like” jaws on an appendage of their human tormentor and stubbornly hang on. As one of my references states, “It is always best to let a sleeping nurse shark lie.”
Nurse sharks are found along both the Atlantic and Pacific coasts of North America and South America, mostly in tropical and sub-tropical waters, as well as along the eastern Atlantic shore in France and Africa. Here on the Eastern Seaboard, they range from Brazil north to Long Island and Rhode Island waters.
The individual I was able to examine, approximately 2 feet in length, was a very young juvenile. At birth they measure 1 foot long and grow an additional half foot per year while young. Their average lifespan is 25 years. At 10 to 20 years, they are fully mature, measuring 8 to 9 feet in length and weighing over 200 pounds. Should a mature individual be provoked and clamp onto your arm or leg, and do its version of the crocodile “death roll,” you could be in trouble!
They generally reside on the sea floor in shallow waters (less than 70 feet deep). Solitary nocturnal predators, they feed on rays, squid, octopus, crabs, lobsters and various bivalves, using several unique strategies to capture prey. Its small mouth combined with its gill muscles and large, bellows-like pharynx can create an incredibly powerful, vacuum-like suction that enables it to catch small fish that are resting at night. Thick-shelled whelks or conchs are turned over and, using suction and teeth, the meat is extracted.
Juveniles often sit still on the sandy bottom, propping themselves up on their pectoral fins to create a cave-like space to lure in crab prey.
During the day, nurse sharks will congregate in groups, resting motionless on the bottom with their heads usually tucked under a rock or coral ledge. Unlike many other shark species, they do not need to be in constant motion for water to pass through their gills; muscles pump water through their mouth and out their gills as they lie still.
This species has been the subject of extensive research and study in Florida, and findings include the fact that it is non-migratory and exhibits strong site fidelity, making it very vulnerable to local extirpation. There is no commercial fishery for nurse sharks in Florida, and because of its relatively docile nature, swimming with this species is a popular form of ecotourism. Yet its abundance in the waters adjacent to Florida has declined—most likely a result of habitat degradation and loss.