Nurse Sharks

The ship was sailing in the deep sea with the diver aboard. The ocean was azure blue. The diver donned his diving gear and plunged into the sea. The ocean was cool and enchanting. He came across fish of various colors, patterns and hues. Suddenly he saw two round objects shining in the distance. They swiftly became bigger. He could make out the contours of an enormous predator. It was a shark attacking an apparent intrusion in its domain. The diver was paralyzed by fright. Then he came to his senses and swam in the opposite direction. The shark made good the distance between them. It opened its jaws to display a serrated set of teeth. The diver was exhausted and closed his eyes expecting to be devoured. The shark to his surprise ignored him and swam past. He took a deep breath thanking his lucky stars.

Not all sharks attack humans. The nurse shark is a type of shark, which attacks humans only when provoked. It is definitely not the Florence Nightingale of the sea. It is a not an aggressive shark and will generally swim away when approached.

Description of Nurse Sharks

Nurse shark's taxonomic name is Ginglymostoma cirratum. They have two spineless, dorsal fins with the second one significantly 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. They are characteristically large and sluggish. They are mainly active in the night (hence called nocturnal creatures). They are generally found motionless resting at the bottom of the ocean floor. They go back to the same caves where they were resting before their activities. They congregate in schools (i.e. groups of fish). If a nurse shark loses its teeth it is replaced.

Occurrence and Reproduction of Nurse Sharks

Nurse sharks are generally found in the Western Atlantic, Eastern Atlantic and the Eastern Pacific oceans. They occur in the coasts of Australia, Uruguay, South Africa, Argentina and the United States. Their favorite habitats are mangrove islands (mangroves are trees and shrubs that grow in saline coastal habitats), coral reefs, rocks and caves. Nurse sharks mate during the summer. Their reproduction is termed ovoviviparous i.e. the embryo will not receive any nutrition from the placenta. The gestation period is around six months. Each female has a maximum of only two live young because the firstborn tries to eat all of its siblings in the uterus, leaving only one in each of the two fallopian tubes.

When they are born they measure 11 to 12 inches. Their adult size varies from 2 to 13 feet. The largest ones are about 14 feet long. They generally weigh about 110 kg. They attain maturity at 15 to 20 years old. They do not migrate when the water turns cooler. They simply become less active.

Diet of Nurse Sharks

Nurse sharks have barbells, which are thin, fleshy, whisker-like organs on the lower jaw in front of the nostrils that sense touch and taste. Barbells help the shark locate their food. They eat octopus, mollusks, sea urchins, squids, spiny lobsters, shrimp, stingrays, puffers and crabs. They eat shelled conchs by flipping them over and getting the snails by biting and sucking. They have thousands of replaceable teeth, which are serrated, and fan shaped.

Predators of Nurse Sharks

Tiger sharks and lemon sharks eat them. Great hammerhead sharks and bull sharks are also known to attack them.

Hunting of Nurse Sharks

Nurse sharks are hunted for their meat. Their skin makes good quality leather. Liver oil is extracted from them. Gray Nurse Sharks (they have a gray back and a white underside) are a type of nurse sharks that were severely depleted due to unrestrained hunting in the 50's, 60's and 70's. Efforts are going on to conserve them.

We should not lose these magnificent Gray Nurse Sharks. It could have drastic effects on the food chain and consequently, the environment. We should preserve them as a nature's gift for posterity.