Nurse Shark, Ginglymostoma cirratum
Nurse Shark, Ginglymostoma cirratum. Fish caught from coastal waters off Big Pine Key, Florida, April 2019. Length: 1.27 m (4 feet 2 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
Nurse Shark, Ginglymostoma cirratum. Fish caught from coastal waters off Islamorada, Florida, February 2020. Length: 1.27 m (4 feet 2 inches). Catch, photograph and identification courtesy of Marc Eberlein, Grand Rapids, Michigan.
The Nurse Shark, Ginglymostoma cirratum, is a member of the Nurse Shark or Ginglymastomatidae Family that is known in Mexico as tiburón gata. Globally, there are two species in the genus Ginglymostoma, both of which are found in Mexican waters, one, this species, in the Atlantic Ocean and one in the Pacific Ocean.
The Nurse Shark has a flattened body which is not the typical torpedo-shaped shark body. The adults vary in color from a yellowish tan to dark brown. The juveniles are covered with small black spots that have lighter colored margins. The juveniles will become lighter in color in full sunlight. They are characterized by having a broad rounded head with very small eyes and a subterminal mouth that is well in front of the eyes that has moderately long nasal barbels on either side and minute spiracles; their anal, dorsal and pectoral fins are broadly rounded; their caudal fin is elongated being greater than 25% of the total length, and does not have a distinct lower lobe first dorsal fin originates well behind the pectoral fins and over or behind the pelvic fins; and, their second dorsal fin is slightly smaller than the first.
The Nurse Shark are found resting on sandy bottoms or in shallow water caves and rock crevices around deeper reefs at depths up to 75 m (245 feet) during the day and move to coastal shallower waters of less than 20 m (65 feet) at night for feeding. They are normally found as solitary individuals but have also been observed in groups of up to 40 individuals. The juveniles are mostly found on the bottom of shallow coral reefs, seagrass flats, and around mangrove islands. The Nurse Sharks are exceptionally sedentary, unlike most other sharks. They have a high site fidelity returning to the same breeding grounds repeatedly. They reach a maximum of 3.08 m (10 feet 1 inch) in length and 109.6 kg (241 lbs) in weight with males being slightly larger than females. As of January 1, 2023, the International Game Fish Association world record stood at 119.6 kg (264 lbs) with the fish caught in coastal waters Port St. Joe, Florida in July 2007. They are normally solitary opportunistic hunters that are suction feeders that consume small fishes including catfishes, mullets, puffers and stingrays and invertebrates (crustaceans, mollusks and tunicates) including bivalves, crabs, spiny lobsters, octopi, sea urchins, shrimps and snails. In turn their juveniles are preyed upon by various larger sharks, including Bull Sharks, Great Hammerhead Sharks, Lemon Sharks, and Tiger Sharks. Females reach sexual maturity at 15 to 20 years and males at 10 to 15 years. Reproduction occurs in biannual cycles and is ovoviviparous with internal fertilization and eggs hatching inside the females. Each female will mate with multiple males. Gestation periods are 5 to 6 months and liter sizes of up to 50 miniature adults that are between 27 cm (11 inches) and 30 cm (12 inches) in length. Their young are born live and capable of fending for themselves and remain in shallow-coastal waters for several months to avoid predation. They have lifespans of twenty-five years.
The Nurse Shark is a resident of all Mexican waters of the Atlantic Ocean including the Gulf of Mexico and the east coast of the Yucatán Peninsula in the Caribbean.
The Nurse Shark is a straightforward identification and is the only large shark that is brown in color. If confused it would be with the Lemon Shark, Negaprion bervirostris (lacks mouth barbels).
From a conservation perspective the Nurse Shark is currently classified as Near Threatened. Today they are not targeted in most parts of their range and not considered to be a quality food fish. Historically they have been targeted for their fins, liver oil and skin to produce leather products, but have become overfished to near extinction in the southern parts of their range. The juveniles are popular within the aquarium trade for use in large public aquariums. Due to their sedimentary nature, they are a target of the ecotourism industry but will normally swim away when approached. They are considered to be an important species for shark research. The Nurse Shark is not considered to be dangerous to humans and will only attack if provoked. Their long-term viability is currently threatened by overfishing, low reproductive rates and inshore habitat destruction caused by human developments.