Nurse sharks may appear lethargic and slow but when disturbed, they can attack quickly and can inflict harm on other creatures. They can lie motionless for a long time, survive mostly on crustaceans and hunt for their food during the night.
The release of the smash hit movie, Jurassic Park, has helped adults rediscover what kids have known all along – dinosaurs are absolutely fascinating. Underwater, the sharks are the divers’ dinosaurs. Twice as old as now extinct dinosaurs, sharks have been around since the Devonian Period – 350 million years ago.
A fine example of an undersea “dinosaur” is the Nurse Shark – one of the most docile sharks to be encountered by divers. Here is a creature that looks incredibly prehistoric yet has survived in great abundance.
Behold The Nurse Shark
The Nurse Shark is one of the Orectolobiformes – a group of sharks with the mouth positioned well in front of their eyes. This physical aspect is one of the major differences between Nurse Sharks and the free swimming Requiem Sharks.
Because this species inhabits inshore coral reefs, lagoons and rocky ledges, it is frequently encountered by divers. In fact, the Nurse Shark is generally the first shark a new diver sees.
The Nurse Shark has a large, rounded head, with a thick body and a skinny tail. It resembles a gigantic tadpole. The eye is very small in proportion to the body – almost bead-like. Two fleshy barbells hang down from the snout, one in front of each nostril.
The fins of the Nurse Shark help give it that prehistoric appearance. The caudal fin (tail) has a large upper lobe and almost no lower lobe. This tail fin design allows the shark to lie on the bottom comfortably or to swim within inches of the bottom without dragging its tail.
The first dorsal fin is way back on the body, even with the pelvic fins. The base of this dorsal is almost as long as its height, The second dorsal starts immediately behind the first and ends at the base of the caudal fin.
The lower fins (pectoral, pelvic and anal) are also quite short but very broad. The shape and arrangement of the Nurse Shark’s fins provide an easy way of identifying this creature.
At a distance, the Nurse Shark appears gray but upclose you will find its color is really brown. Color shades can range from tan to almost a rich chocolate brown. The underside is usually a creamy white.
The color is fairly uniform across the entire body but juveniles may have small black spots. Variations in color may be partly owing to the ambient light. The tone can be pale while the shark is in the shadows of a cave or under a ledge but the same animal can become darker when exposed to stronger sunlight.
The Nurse Shark can range in size from 6 to 12 feet. Maximum possible length is approximately 14 feet. Nurse Sharks that reach a length of 10 to 1 2 feet are very heavy bodied – almost the breadth of a cow.
The Nurse Shark is a member of the family Ginglymostomatidae – which has only three species. They are all bottom dwellers that tend to lie in crevices, under ledges, in coral caves or under shipwrecks. The Nurse Shark shown here is G. cirratum, probably the most abundant of the three.
The Nurse Shark is very distinctive in its shape and color. This shark is rarely confused with other shark species in the same region. The only other species that look similar are the Indo-Pacific and Tawny Nurse Sharks, both found in the Pacific, and the Shorttailed Nurse Shark found in the Indian Ocean.
The Nurse Shark has an extremely wide range in the Atlantic Ocean, as well as certain portions of the Pacific. It can be found in the Western Atlantic from Rhode Island to Brazil. it is also found in the eastern Atlantic from Senegal to Gabon (Africa), and in the eastern Pacific from southern Baja California to Peru.
The Nurse Shark inhabits the shallow reef and rock areas from the inter-tidal zone to a depth of 1 65 feet. It is often found in coral caves in waters ranging from 20 to 60 feet deep and this is why it is so frequently encountered by divers.
The Nurse Shark can lie motionless on the bottom for long periods of time while breathing through its mouth and gills. During the day, it remains inactive-appearing to be asleep under a ledge or in a cave. If it cannot find refuge in a cave, it will seek a narrow crevice or depression in the seafloor.
Nurse Sharks can be encountered either singly or in groups. It is not uncommon to find two or three Nurse Sharks occupying the same coral cave. Divers have also reported finding Nurse Sharks in narrow crevices, piled on top of each other in random positions – stacked like logs.
The Nurse Shark is a nocturnal feeder. At night, it hunts for lobsters, crabs or other crustaceans. This animal has small teeth and a powerful jaw designed for holding and crushing. It will suck its prey into its mouth with a strong vacuum force, then crush and swallow the victim.
The Nurse Shark has quite a varied diet. It will feed on small fish, octopus and sea urchins but its favorite food is Spiny Lobsters. It will often dig under pieces of coral in search of food. When necessary, it can be a scavenger – feeding on dead fish on the bottom. The Nurse Shark is deceptive in appearance and behavior. During the day it looks lethargic, lazy or asleep. When disturbed it will move over, reverse its position or swim slowly away. Because of the design of its tail, this fish swims in an eel-like manner – snaking its way through the water.
Divers should not be fooled by this sluggish behavior. If harassed, the Nurse Shark can react with lightning speed. It is very agile as well as quick. If a diver pulls or grabs its tail, the Nurse Shark can reach around and bite the hand that holds it.
The Nurse Shark is not aggressive toward divers and prefers to be left alone. It does not have sharp cutting teeth like Requiem Sharks. instead, it has small teeth but a very powerful jaw. When harassed or molested the Nurse Shark will bite. It can clamp down on a diver’s arm, leg or hand with incredible power – causing excruciating pain. In some cases, attempts to get the shark to release its grip have failed and the diver is dragged from the water with the shark still holding on. Sometimes the shark has to be killed and the vice-like jaws pried apart in order to free the diver.
Should you encounter this prehistoric creature underwater, the best advice is “look but don’t touch.”