Nurse shark (Ginglymostoma cirratum) is a species of shark found in the Western Atlantic, Eastern Atlantic, and the Eastern Pacific oceans. They occur along the coasts of Australia, Uruguay, South Africa, Argentina, and the United States, where they are found in the vicinity of mangrove islands, coral reefs, rocks, and caves.
Nurse sharks are typically characterized by their two spineless, dorsal fins, of which the second is slightly smaller than the first. They are usually dark brown or light yellow in color. Young nurse sharks have small dark spots on their entire body. These sharks are characteristically large and sluggish. When they are born, they measure 11 to 12 inches. At full growth though, their length varies from 2 to 13 feet. The largest of this species are about 14-feet long. They generally weigh about 110 kg.
They are nocturnal creatures, i.e., mainly active at night, and are generally found motionless resting at the bottom of the ocean floor. These sharks congregate in schools, i.e., groups of fish, and retreat to the same caves for resting. They do not migrate when the water gets cold. Instead, they simply become less active.
Nurse sharks attain maturity at 15 to 20 years and mate during the summer. Their reproduction is termed 'ovoviviparous', wherein the embryo does not receive any nutrition from the placenta. The gestation period is around six months. Each female has a maximum of only two live young ones, as the firstborns try to eat their siblings in the uterus, leaving only one in each of the two fallopian tubes.
Nurse sharks have barbells, which are thin, fleshy, whisker-like organs on their lower jaw (in front of the nostrils) that they use to locate their food. They eat octopus, mollusks, sea urchins, squids, spiny lobsters, shrimp, stingrays, puffers, and crabs. They are also known to feed on shelled conchs―a seemingly impossible feat these sharks achieve by flipping them over and sucking the snail out. They have thousands of replaceable teeth, which are serrated and fan-shaped; these play a crucial role in their diverse diet.
Nurse sharks are threatened by predators like tiger sharks and lemon sharks. Great hammerhead sharks and bull sharks are also known to attack them, though the instances are rare. Additionally, nurse sharks are hunted by humans for their meat, skin (which makes good quality leather), and liver oil. At the ongoing rate, we are set to lose them sooner or later, and that will have drastic effects on the food chain and consequently, the marine environment.