Nurse Shark

The nurse shark genus Ginglymostoma is derived from 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. The name "nurse" may have originated from antiquated spelling conventions. The Oxford English Dictionary notes that, in medieval times, the "n" of the word "an" was frequently transferred to a following word that began with a vowel. Huss, husse and hurse were antiquated names for dogfish and other sharks. Another possibility is noted by Lineaweaver and Backus in The Natural History of Sharks, which posits instead that the name comes from the fact that the nurse shark is ovoviviparous. "Possibly, some bygone observer watched a shark giving birth to live young and thought the shark was giving nurse."

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). and in the East Pacific from Baja California to Peru. Nurse sharks are also subject to piebaldism, a genetic condition that results in a partial lack of body pigmentation and a speckled body.

Nurse sharks are opportunistic predators that feed primarily on small fish (e.g. stingrays, teleosts) and some invertebrates (e.g. crustaceans, molluscs, sea urchins, tunicates, anthozoans), as well as algae. They are typically solitary nocturnal animals, rifling through bottom sediments in search of food at night, but are 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. American alligators (Alligator mississippiensis) and American crocodiles (Crocodylus acutus) may occasionally prey on nurse sharks in some coastal habitats. Photographic evidence and historical accounts suggest that encounters between species are commonplace in their shared habitats.

Nurse sharks are ovoviviparous, with fertilized eggs hatching inside the female. The mating cycle of nurse sharks is biennial, with females taking up to 18 months to produce a new 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 21–29 pups.