Nurse Sharks, The Original Bottom Feeder
Nurse sharks are commonly found in shallow, sub-tropical and tropical waters. Their range is from Rhode Island to Brazil, including the Gulf of Mexico, the Indo-Pacific in Philippines and the Caribbean Sea. Rarely are they found north of Cape Hatteras. They frequently dwell on rocky and coral reefs, and in channels between mangroves keys and sand flats. Examples of the nurse shark species are the Pacific Sleeper Shark, Tawny nurse shark and the Zebra shark.
Nurse sharks are bottom-dwellers and they are typically slow-moving, sluggish and docile. They are sociable, and they can be found sleeping in groups. The tawny nurse sharks tend to vary in color from yellowish-tan to dark brown. Their average size is around 8 to 9 feet long and over 200 pounds. Nurse sharks are nocturnal by nature and hunt on the bottom of the sea. They eat stingrays, crustaceans, octopi, squids, shrimp, clams and mollusk.
Nurse sharks are an ancient species and they are not as active as modern species of sharks. Ancient shark species breath using buccal pumping which is named for the buccal, or cheek, muscles that pull the water into the mouth and over the gills. By contrast, modern sharks breathe through a technique called ram ventilation which requires them to swim and force water into their mouths to process. Most modern sharks, however, can employ buccal pumping and ram ventilation as needed.
The nurse shark has a caudal (tail) fin which can be one fourth of the length of their body. The bottom, pectoral fin helps the nurse shark to hover and sometimes the nurse shark will provide a shelter for crabs and other shellfish which the nurse shark can then ambush.
At times, when the nurse shark hunts, it can appear to be walking along the ocean floor with its pectoral fins. Often a nurse sharks stomach contents do not contain much food. This indicates that the nurse shark’s lethargic, idle nature does not require as much food as active modern sharks.
Nurse sharks are not known to be dangerous to humans unless provoked. They have strong jaws and thousands of tiny, serrated teeth, and they will bite if stepped on or bothered by divers. There is no record of fatalities, but a nurse sharks mouth is attached to a large pharynx the allows it to suck up food and the nurse shark bite can be very harmful.
Nurse sharks can latch onto its victim with a vice-like grip that may require surgical instruments to remove it. According to George Burgess, Director, International Shark Attack File, “A nurse shark bite is one of the worst because their teeth are like cheese graters on each side,” and they suck food into their mouth, grinding up tissue as they go, Burgess says. “When they get onto a human being, it’s like a vacuum cleaner.… They leave a concave hole where they’ve turned flesh into hamburger.” However, nurse sharks typically demonstrate shy, non-aggressive behavior.
People often wonder how did they get the name nurse shark. Some say the name nurse shark is derived from the old English word “hurse” which translates to “sea-floor shark.” Others claim it gets its name from Grecian etymology and an archaic word, “nusse”, meaning cat shark. In Caribbean waters, the nurse shark is often referred as "tiburon gato" or cat-shark.
In observation, the snout of the nurse shark appears to be cat-like because it has flexible nasal barbels on each side of its mouth near the tip of its snout. The barbels help the nurse shark to sniff out food in the sand. Finally, though, some say the nurse shark name may come from the strange sucking or “nursing” sounds they make when searching for prey in the sand. Whatever the source, it is long forgotten, as this ancient shark species lies in wait on the bottom of the sea.