The nurse shark (Ginglymostoma cirratum) is an elasmobranch fish within the family Ginglymostomatidae. They are directly targeted in some fisheries and considered as bycatch in others. Nurse shark conservation status is globally assessed as being Data Deficient due to the lack of information across its range in the Eastern Pacific and Eastern Atlantic. They are considered to be Near Threatened in the Western Atlantic due to their vulnerable status in South America and reported threats throughout many areas of Central America and the Caribbean; and they are considered to be a species of Least Concern in the U.S. and Bahamas.
Taxonomy
The nurse shark genus Ginglymostoma is derived from the Greek language meaning hinged mouth, whereas the species cirratum is derived from Latin meaning having curled ringlets. Based on morphological similarities, Ginglymostoma is believed to be the sister genus of Nebrius, with both being placed in a clade that also include species Pseudoginglymostoma brevicaudatum, Rhincodon typus, and Stegostoma fasciatum.
Description
The nurse shark has two rounded dorsal fins, rounded pectoral fins, an elongated caudal fin, and a broad head. Maximum adult length is currently documented as 3.08Â m (10.1Â ft), whereas past reports of 4.5Â m (15Â ft) and corresponding weights of up to 330Â kg (730Â lb) are likely to have been exaggerated. Adult nurse sharks are brownish in color. Newly born nurse sharks have a spotted coloration which fades with age and are about 30Â cm in length when nascent.
Distribution and habitat
The nurse shark has a wide but patchy geographical distribution along tropical and subtropical coastal waters of the Eastern Atlantic, Western Atlantic, and Eastern Pacific. In the Eastern Atlantic it ranges from Cape Verde to Gabon (accidental north to France). In the Western Atlantic, including the Caribbean, it ranges from Rhode Island to southern Brazil., and in the East Pacific from Baja California to Peru.
Nurse sharks are a typically inshore bottom-dwelling species. Juveniles are mostly found on the bottom of shallow coral reefs, seagrass flats, and around mangrove islands, whereas older individuals typically reside in and around deeper reefs and rocky areas, where they tend to seek shelter in crevices and under ledges during the day and leave their shelter at night to feed on the seabed in shallower areas.
Biology and ecology
Nurse sharks are opportunistic predators that feed primarily on small fish (e.g. stingrays) and some invertebrates (e.g. crustaceans, molluscs, tunicates). They are typically solitary nocturnal animals, rifling through bottom sediments in search of food at night, but often gregarious during the day forming large sedentary groups. Nurse sharks are obligate suction feeders capable of generating suction forces that are among the highest recorded for any aquatic vertebrate to date. Although their small mouths may limit the size of prey, they can exhibit a suck-and-spit behavior and/or shake their head violently to reduce the size of food items.
Nurse sharks are exceptionally sedentary unlike most other shark species. Nurse sharks show strong site fidelity (typical of reef sharks), and it is one of the few shark species known to exhibit mating site fidelity, as they will return to the same breeding grounds time and time again.
Reproduction
Nurse sharks are ovoviviparous, producing young by means of eggs that are hatched within the body of the pregnant female. The mating cycle is biennial, taking 18 months for the female's ovaries to produce another batch of eggs. The mating season runs from late June to the end of July, with a gestation period of six months and a typical litter of 21â€"29 pups. The young nurse sharks are born fully developed at about 30 cm long.
See also
- List of sharks
- List of prehistoric cartilaginous fish