| Nurse shark Temporal range: 112–0 Ma Albian to Present[1] |
|
|---|---|
| Ginglymostoma cirratum | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Order: | Orectolobiformes |
| Family: | Ginglymostomatidae |
| Genus: | Ginglymostoma J. P. Müller and Henle, 1837 |
| Binomial name | |
| Ginglymostoma cirratum (Bonnaterre, 1788) |
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| Range of nurse shark (in blue) | |
The nurse shark, Ginglymostoma cirratum, is a shark in the nurse sharks (Ginglymostomatidae) family, the only member of its genus Ginglymostoma. Nurse sharks can reach a length of 4.3 m (14 ft) and a weight of 330 lbs (150 kg).[2]
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The nurse shark family name, Ginglymostomatidae, derives from the Greek: from γίγγλυμος meaning hinge and στόμα meaning mouth. Cirratum also derives from Greek, meaning curl or swim. Based on morphological similarities, Ginglymostoma is believed to be the sister genus of Nebrius, with both being placed in a clade that also contains the short-tail nurse shark (Pseudoginglymostoma brevicaudatum), the whale shark (Rhincodon typus), and the zebra shark (Stegostoma fasciatum).[3]
The nurse shark is a common inshore bottom-dwelling shark, found in tropical and subtropical waters on the continental and insular shelves. It is frequently found at depths of one meter or less but may occur down to 75 m. Its common habitats are reefs, channels between mangrove islands and sand flats. It occurs in the Western Atlantic from Rhode Island down to southern Brazil; in the Eastern Atlantic from Cameroon to Gabon (and possibly ranges further north and south); in the Eastern Pacific from the southern Baja California to Peru; and around the islands of the Caribbean.[4]
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. Nurse sharks are also known to graze algae and coral.
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.[4]
Nurse sharks are able to respire while stationary by pumping water through their mouths and out gills.
The mating season runs from late June to the end of July. Nurse sharks are ovoviviparous, meaning the eggs develop and hatch within the body of the female where the hatchlings develop further until live birth occurs. The gestation period is six months, with a typical litter of 21 - 29 pups.[4] The mating cycle is biennial, as it takes 18 months for the female's ovaries to produce another batch of eggs, during which time, cannibalistic behavior can occur. The young nurse sharks are born fully developed at about 30 cm long in Ginglymostoma cirratum. They possess a spotted coloration which fades with age.
The nurse shark is not widely commercially fished, but because of its sluggish behaviour it is an easy target for local fisheries. Its skin is exceptionally tough and is prized for leather; its flesh is consumed fresh and salted and its liver is utilised for oil. It is not taken as a game fish. It has been reported in some unprovoked attacks on humans but is not generally perceived as a threat. One such reported attack took place off the coast of San Pedro, Ambergris Caye at a dive site known as "Esmeralda." [4]
Juvenile nurse sharks are sometimes sold in the saltwater aquarium trade.[5] However, since nurse sharks attain lengths in excess of ten feet they are far too large to be kept in home aquaria.[5] In an article for Aquarium Fish Magazine, Scott W. Michael criticizes the ethics of aquarists attempting to keep species beyond their spatial and financial means.[5] He also notes that most public aquaria are not interested in taking specimens that have outgrown home aquaria and that they should never be released into the wild.[5]