The Nurse shark (Ginglymostoma cirratum) is a shark belonging to the family Ginglymostomatidae. They have several ranges and have been typically quite common even right here in Florida and the Caribbean. They are highly social sharks, but typically rest in groups by day and are active by night. The Nurse shark has one of the highest suction scales on the RSI of any shark. They aren’t typically a threat, but will defend themselves and since they suck and never let go, their bite can be quite painful and inflict some damage. The Nurse shark is quite popular among divers and ecotourism.
Family: Ginglymostomatidae – Nurse Sharks
Genus: Ginglymostoma
Species: cirratum
Phylum– Chordata
Class– Chondrichthyles
Common Name– Carpet Sharks
Family– Ginglymostomatidae
Common Name– Nurse Sharks
Genus– Ginglymostoma
Species– cirratum
Status: IUCN Red List DATA DEFICIENT
Average Size and Length: They are born between 27-30 cm/10.6-11.8 inches. Mature males have been measured at 210 cm/6.9 feet. Mature females have been measured between 230-240 cm/7.5-7.9 feet. The maximum recorded length has been 300 cm/9.8 feet. There is a possibility of one measuring 430 cm/14.1 feet, but this is probably exaggerated.
Average Weight: The heaviest recorded weight has been 243 pounds. There are reports of heavier, but these are not confirmed.
Current Rare Mythical Sightings: The origin of the name “Nurse shark” is uncertain. It may come from the sucking sound they make when hunting for prey in the sand, which vaguely resembles that of a nursing baby. Or it may derive from an archaic word, “nusse”, meaning cat shark. The most likely theory though is that the name comes from the Old English word for sea-floor shark: “hurse”.
Teeth and Jaw: The mouth is small and subterminal. The Nurse shark possess an independent dentition, the simplest type of tooth arrangement found in sharks where there is no overlap between teeth. This allows forward movement of replacement teeth that is independent of adjacent teeth in the jaw. The teeth are serrated. Check out this video of the mouth, teeth and nasoral barbels here.
Head: There are long barbels and nasoral grooves. The mouth sits in front of the dorsal lateral eyes. There are tiny spiracles behind the small eyes.
Denticles: The Nurse shark dermal denticles are typically thick and diamond-shaped with a single peak and are positioned side-by-side along the skin. Some of them lack ridges, but some have large, widely spaced and incomplete ridges. The ridge spacing is significantly wider than that observed for other reef-associated shark families.
Tail: The precaudal tail is shorter than the head and the body. The caudal fin is elongated and is greater than 25% of the total length.
Demographic, Distribution, Habitat, Environment and Range: Nurse sharks have several wide ranged. In the east Pacific, they can be found from Mexico to Peru. In the west Atlantic, they can be found in the USA to the Gulf, Caribbean and Brazil. In the east Atlantic, they can be found from Cape Verde Islands, Senegal, Cameroon, to Gabon. They are rarely found to the North of France. They typically can be found over rocky or coral reefs, in channels between mangrove keys and sand flats on tropical and subtropical continental and insular shelves from less than 1 foot to 39 feet. They have been found between 131-427 feet off Brazil. Their home range is small.
Juvenile nursery areas are in shallow turtle-grass beds and coral reefs.
Diet: They feed on bottom invertebrates, stingrays, bony fish and other opportunistic prey. They can even extract conch from their intact shells.
Nurse sharks are occasionally prey for American alligators (Alligator mississippiensis) where they share the same habitat. Recent studies based on photographs and historical accounts indicate that these encounters may be more common than previously thought. In addition, larger sharks may prey upon them.
Ram-Suction Index: Nurse sharks are obligate suction feeders capable of generating suction forces that are among the highest recorded for any aquatic vertebrate to date. They may also shake their head violently to rip off smaller, digestible sizes of prey, or suck and spit. They suck prey in rapidly with their very small mouths and large pharynx.
Aesthetic Identification: Adult Nurse sharks are uniform yellow to grey-brown. The young sharks have small, dark, light-ringed ocellar spots and obscure saddle markings. The dorsal fins of the Nurse shark are broadly rounded. The first dorsal fin is much larger than the second dorsal fin and anal fins.
Biology and Reproduction: The Nurse shark is ovoviviparous. They have between 20-30 pups per litter, with large yolk-sacks. They are born in late spring to summer after a 5 to 6-month gestation period. Females reproduce every other year.
Males mature at 10-15 years of age, and females at 15-20 years if age.
Nematodes have been observed in the gills of nurse sharks in captivity at the New York Aquarium.
Behavioral Traits, Sensing and Intelligence: Nurse sharks are Nocturnal. They are also social sharks. They can be found resting in groups, sometimes even piles by day in preferred shallow water locations in caves or on sand. They are highly active at night. Check out this video of an example of Nurse shark social feeding, even with a manatee.
They have been known to use their muscular pectoral fins to climb or clamber on the bottom and snout to root out prey. They prop up on them, head up, sucking in prey.
Their courtship and mating behavior are interesting. They engage in parallel synchronized swimming with their sides almost touching. The male Nurse shark will be besides, or slightly behind or below the female. The male will then bite one of the female’s pectoral fins and both will roll upside-down. This is the point they will mate, and they stay close to the sea bed.
Nurse sharks show strong site loyalty, and it is one of the few shark species known to display mating site fidelity. They are known to return to the same mating grounds over and over again.
Nurse sharks are an important species for shark research predominantly in physiology. They are robust and able to tolerate capture, handling, and tagging extremely well.
Speed: They are strong swimming at night. Based on their dermal denticles, they are slower swimming sharks.
Nurse Shark Future and Conservation: Currently, the Nurse shark is not evaluated. Historically, they were common in many areas. Their small home ranges and aggregating habits make it highly vulnerable to local extirpation. They are popular with divers and ecotourism, and hardy in public aquaria.
Nurse Shark Recorded Attacks on Humans: They are typically docile with humans, will bite if provoked or if needed to defend themselves. They have strong suction, and do not let go so their bites can pack a lasting and powerful punch. They are ranked high in human shark bites, in the past as high as 4th.