The origin of the name "nurse shark" is unclear. It may come from the sucking sound they make when hunting for prey in the sand, which vaguely resembles that of a nursing baby. Or it may derive from an archaic word, nusse, meaning cat shark. The most likely theory though is that the name comes from the Old English word for sea-floor shark: hurse.
The nurse shark has two rounded dorsal fins, rounded pectoral fins, an elongated caudal fin, and a broad head. Nurse sharks are brownish in color. Maximum adult length established by reliable reports is 3.08 m (10.1 ft); earlier reports of lengths up to 4.5 m (15 ft) and corresponding weights of up to 330 kg (730 lb) are likely to have been exaggerated
Nurse sharks are slow-moving bottom-dwellers and are, for the most part, harmless to humans. However, they can be huge—up to 14 feet (4.3 meters)—and have very strong jaws filled with thousands of tiny, serrated teeth, and will bite defensively if stepped on or bothered by divers who assume they’re docile. They use their strong jaws to crush and eat shellfish and even coral, but prefer to dine on fish, shrimp, and squid. They are gray-brown and have distinctive tail fins that can be up to one-fourth their total length. Unlike most other sharks, nurses are smooth to the touch.
Biology and Ecology Edit
Nurse sharks are found in the warm, shallow waters of the western Atlantic and eastern Pacific oceans. They are abundant throughout their range and have no special conservation status, although the closeness of their habit to human activities is putting pressure on the species.
Nurse sharks are nocturnal animals, spending the day in large inactive groups of up to 40 individuals. Hidden under submerged ledges or in crevices within the reef, the nurse sharks seem to prefer specific resting sites and will return to them each day after the night's hunting. By night, the sharks are largely solitary; they spend most of their time rifling through the bottom sediments in search of food. Their diet consists primarily of crustaceans, molluscs, tunicates, sea snakes, and other fish, particularly stingrays.
They are thought to take advantage of dormant fish which would otherwise be too fast for the sharks to catch; although their small mouths limit the size of prey items, the sharks have large throat cavities which are used as a sort of bellows valve. In this way nurse sharks are able to suck in their prey with a short, violent influx of water. Nurse sharks are also known to consume algae and coral, although this may be the by-catch caused by their method of eating.
Nurse sharks have been observed resting on the bottom with their bodies supported on their fins, possibly providing a false shelter for crustaceans which they then ambush and eat. Nurse sharks are able to respire while stationary by pumping water through their mouths and out gills.
It was shown that compared to sharks such as the shortfin mako shark, nurse sharks only use about eighteen percent of the energy a more active predatory shark would use. Due to their lower metabolic rates as well as their ability to have relatively larger litters of pups that grow faster compared to the offspring of other sharks, they are often one of the most common shark species in tropical to sub-tropical waters.