Nurse Shark

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Nurse Shark

Since this is one of the most studied sharks, the main mystery that remains is the origin of its name. There are three theories to what it could be. The first, and most common, is that the shark is named for the sucking sound it makes as it hunts, possibly resembling a nursing baby. The other two theories involve archaic words - ‘nusse’ and ‘hurse’. Nusse refers to catsharks, which is still a term applied to nurse sharks in Caribbean waters, where they are called "tiburon gato". Hurse is an Old English word for sea-floor shark.


Content List

1. Scientific & Common Names

2. Characteristics

a. Breeding

b. Behavior

3. History

4. Present Status

5. References


Scientific & Common Names

Kingdom - Animalia

Phylum - Chordata

Class - Chondrichthyes

Subclass - Elasmobranchii

Order - Orectolobiformes

Family - Ginglymostomatidae

Genus – Ginglymostoma

Species – G. cirratum

Common Names – Nurse Shark, Cat Shark


Characteristics

Nurse sharks can reach sizes between 9-14 feet, with 6-8 being more common. They can also weigh over 300 pounds. While adults are generally a yellowish to darker brown, juveniles can have dark spots with lighter rings. Nurse sharks are slow moving bottom dwellers who tend to restrict their actives to the night. Their small mouths are located on the underside of their snout, and are barely visible when they are resting on the bottom. Despite the small size of their mouth and their generally docile nature, they have a powerful bite and a multitude of very sharp teeth. Adult nurse sharks have few natural enemies, but larger sharks such as lemons, bulls, tiger, and great hammerheads will sometimes hunt them. They are found in shallow, warm coastal waters in both the Atlantic and the eastern Pacific.


Breeding

The reproduction habits of nurse sharks are among the most studied and understood of all sharks. Males – often many, forcing the females to sometimes flee the melee – approach the lounging females and bite her pectoral fins in an effort to turn her on her side. Most adult females bear multiple scars from this behavior. After fertilization, the embryos develop inside the mother in independent egg sacks, receiving nourishment only from the yolk and not the mother, this is called ovoviviparous reproduction. Six months later, in the spring or early summer, the nurse shark will then give birth to 20-30 live pups, each slightly less than a foot long. This cycle repeats every two years.


Behavior

Nurse sharks are nocturnal animals and nearly all their activity occurs at night, when they become much more energetic swimmers. During the day, they remain resting, sometimes in groups of a few dozen that can pile on top of each other. They often feed by sucking their prey into their mouths, which is most helpful with fish hiding in coral or with conchs. They find most of their prey in sandy bottoms, including sting rays, crustaceans, and mollusks. Bites on humans are not unheard of, but none have been fatal and the majority were considered to be provoked attacks where the animal was handled or aggravated. Only ten unprovoked attacks are list on the International Shark Attack File.


History

Nurse sharks have never been hunted in great numbers, but there is a history of using their hides for leather and their liver oil for lamps and other purposes.


Present status

While there has been a decrease in their numbers, they are not considered currently at risk, unlike many other species of shark.


References

International Shark Attack File: Florida Museum of Natural History, University of Florida

The Book of Sharks by Richard Ellis

The Shark Handbook: The Essential Guide for Understanding the Sharks of the World by Dr. Greg Skomal, Nick Caloyianis(Photographer)

The Encyclopedia of Sharks by Steve Parker

Sharks: History and Biology of the Lords of the Sea by Angelo Mojetta