Ginglymostoma cirratum, more commonly known as nurse sharks, are one of the more sluggish shark species. They can grow anywhere from 7.5 to 14 feet (2.2 to 4.3 meters) in length and weigh 198 to 330 pounds (90 to 150 kilograms). They have very strong jaws that contain thousands of tiny serrated teeth. Unlike most sharks, nurse sharks do not need to constantly be moving in order to move water over their gills and maintain a sufficient internal blood pressure. They often remain motionless on the bottom and will continually open and close their mouths in order to move water over their gills.
Nurse sharks can be found in North America, South America, the east coast of Africa and the Caribbean Islands. They are bottom-dwellers and are found in tropical and subtropical waters around the continental shelves. Nurse sharks are usually seen at depths of 3 feet (1 meter), but have been known to dive down up to 39 feet (12 meters) into the ocean. They tend to live where food is abundant such as reefs, channels between mangrove islands and sand flats. They are nocturnal and are mostly inactive during the day. Rather than just resting anywhere, they have preferred resting spots (usually in crevices in rocks and reefs) which they return to daily. Nurse sharks can be found in groups of up to 40 individuals during the day, but they are solitary hunters.
Nurse sharks feed on a variety of oceanic inhabitants including fish, sea urchins, shrimp, stingrays, octopuses and squid. They will also eat shellfish and even coral, using their powerful jaws to crush them. They are able to inhale their prey into their mouths with tremendous speed and force. Of course, their fast reflexes and quiet approach also make them considerable hunters. Since nurse sharks are active at night, they are able to catch sleeping fish that would be unobtainable during the day.
Mating season for nurse sharks takes place in early summer. Females have a gestation period of 9 months. During that time, the eggs inside them develop and hatch which results in female nurse sharks giving birth to live young. They will give birth to anywhere from 20 to 28 young ones (called pups) each year. The pups measure about 12 inches (30 centimeters), but are otherwise fully developed. If they survive, they can live to be 25 years old.
Nurse sharks are relatively harmless to humans. Although there have been reports of attacks, almost all of them have been the result of divers venturing too close. These sharks will bite if they feel threatened or provoked, although they will not eat people. Although nurse sharks are not listed as endangered or threatened (global population figures are actually unknown), their closeness to human activities has put some pressure on the species. Hopefully, this unique shark never has to worry about population decline and survives long into the future.
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