Nurse Shark

The Nurse Shark (Ginglymostoma cirratum) is a large, sluggish, bottom-dwelling shark that is generally harmless unless provoked. It has very strong jaws, a stout body, and a wide head with obvious barbels (thin, fleshy, whisker-like organs on the lower jaw in front of the nostrils that sense touch and taste). The fourth and fifth gill slits are very close together. The dorsal fins (on the shark's back) are almost the same size and are rounded. Behind each eye there is a spiracle, an organ that takes in water used for breathing when the shark rests at the bottom.

Female nurse sharks, averaging 7½ to 9 feet (2.2 to 2.7 m) and 165 to 230 pounds (75 to 105 kg), are slightly larger than their male counterparts.

The estimated age at maturity for these animals is 18 years for males and 20 to 22 years for females.

Adult nurse sharks generally range from light yellowish tan to dark brown in color. Juveniles up to 23 in (60 cm) have small black spots, with an area of lighter pigmentation surrounding each spot, covering the entire body. These are bands of lighter and darker pigmentation along the dorsal surface. Juveniles (28-48 in / 70-120 cm) are capable of limited color changes. In a tank experiment small nurse sharks, covered for just a few minutes became considerably lighter than individuals exposed to full sunlight. Unusually pigmented individuals (e.g. brilliant yellow or milky white) have been reported several times.

Common in the Atlantic and in the eastern Pacific, in coastal tropical and sub-tropical waters. Reported from Senegal to Gabon, Rhode Island to Southern Brazil, and Mexico to Peru. Also, some individuals have been reported in the Gulf of Gascogne in southwest France. This species is locally very common in shallow waters throughout the West Indies, south Florida and the Florida Keys. Apart of the eastern Pacific, the nurse shark is absent from the Indo-Pacific area, where other related groups have successfully evolved.

The nurse shark is a nocturnal animal that rests on sandy bottoms or in caves or crevices in rock in shallow waters during the day. They occasionally occur in groups of up to 40 individual, as they lie very close together sometimes even piling upon one another.

Nurse sharks are very active during the night. In addition to swimming near the bottom or well off it, the nurse shark can clamber on the sea floor, using its flexible, muscular pectoral fins as limbs. Large juveniles and adults are usually found around deeper reefs and rocky areas at depths of 3-75 meters (10-250 ft) during the daytime and migrate into shallower waters of less than 20 meters (70 ft) deep after darkness.

Juveniles up to 170 cm (6 ft) are generally found around shallow coral reefs, grass flats or mangrove islands in 1-4 meters (3-13 ft) of water. They often lie in groups within limestone solution holes or under rock ledges.

Nurse sharks show a strong preference for certain resting sites, and repeatedly return to the same caves and crevices after a nocturnal activity.