Saturday, October 22, 2011

Life of Nurse Shark

Life of Sea | Nurse Shark (Ginglymostoma cirratum) | The Nurse shark is a common coastal bottom-dwelling shark, found in tropical and subtropical waters on the continental and insular shelves. It occurs in the western Atlantic from Rhode Island to the south of Brazil, in the eastern Atlantic from Cameroon to Gabon, in the eastern Pacific from southern Baja California to Peru and around the islands of the Caribbean. Nurse shark is often found at a depth of one meter or less, but can occur up to 75 m. The common habitats are reefs, channels between mangrove islands and sand flats. Nurse sharks show a strong preference for certain resting sites and repeated the same caves and crevices to return after nighttime activity.

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 

Nurse shark reaches a maximum of 4.3 m total length, maximum weight is 110 kg. The Nurse shark is a common soil-dwelling reef shark found in brackish and marine environments in the shallow waters to 100 m. It has moderately long barbels between the nostrils, nasoral (the nostrils) grooves are present, the mouth is good for eyes, small spiracles, the precaudal tail is shorter than the head and body, the dorsal fins broadly rounded (the first much larger than the second and anal fins), tail moderately long, more than one fourth of the total body length, yellow brown to gray-brown in color, with or without small dark spots and obscure dorsal saddle markings.

Nurse sharks spend the day in large inactive groups of up to 40 people. Hidden under submerged ledges or in crevices in the reef, the nurse sharks seem to prefer specific places calm and return to them every day after the hunt of the night. At night, the sharks are largely solitary, they spend most of their time threaded through the bottom sediments in search of food. Nurse shark are nocturnal, feeding on soil invertebrates such as lobsters, shrimps, crabs, sea urchins, squid, octopus, snails and clams, and fish such as catfish, mullet, puffers and stingrays.

Nurse sharks are not aggressive and will generally swim away when approached, they are one of the most docile animals in the sea. However, some unprovoked attacks on swimmers and divers have been reported. If disturbed the bite is powerful and capable of inflicting serious injury. In some cases, loose jaws reached only after using surgical instruments. 

It is not true that all sharks must swim to breathe, and if they can not for whatever reason, they die. Sharks breathe primarily through a ram-jet ventilation used while swimming. Some sharks, however, half respiratory system is based on pumping water. Nurse sharks can switch to the airways when they are resting and saving and the need to swim to water and oxygen move their gills. This double airways is particularly important for ground dwellers such as the Nurse sharks.

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