Marine Wildlife Encyclopedia
Nurse Shark Ginglymostoma cirratum
Species ID: G.GC
Description: A wide-bodied shark with a flattened, blunt head and barbels above its mouth. The pectoral fins are broad and two large dorsal fins are located towards the rear of the body near the un-forked tail. Nurse sharks are grey to brown in colour. Males differ from females by the presence of external sexual organs called ‘claspers’, fingerlike projections on the ends of the pelvic fins. Juveniles resemble adults but are covered in small dark spots which disappear with age
Maximum Size: 4.3 m (14 ft)
Longevity: Up to 25 years
Status: IUCN endangered species convention currently lacks sufficient data to assess the conservation status of this species
Nurse Sharks & People: The nurse shark is sometimes collected for public aquariums. This is generally a docile species, although reports exist of biting accidents when this species is harassed or accidentally stepped on
Geographical Range: Occasional in shallow tropical waters on both sides of the Atlantic Ocean as well as in the shallow waters of the Eastern Pacific along the coast of California
Coral Reef Zone: Found in the back reef, fore reef and drop-off zones
Favourite Habitat: Nurse sharks prefer sandy areas in which to rest and hunt, as well as rocky areas that offer ledges or caves for shelter
Depth Range: 0-130 m (0-430 ft)
A Day in the Life:
Dawn: Feeding activity declines and nurse sharks seek shelter
Day: These nocturnal animals are sluggish and are usually found resting in caves
Dusk: Nurse sharks emerge from shelter, and move towards shallower areas to forage
Night: At night, nurse sharks actively forage for prey in relatively shallow reef areas
Who Eats Who
The nurse shark feeds on hard-shelled prey such as lobster, crabs, conch, and sometimes squid and fishes. Because it is so big, the nurse shark has few natural predators; it is consumed only by larger shark species.
Scuba Diver & Snorkeler Best Practices
Participate in scientific underwater assessment projects Science matters—advanced divers may wish to participate in fish or coral censuses. Assessments such as these help scientists and marine managers take ‘the pulse’ of coral reefs. Not only will you experience the pleasure of diving, but you will also know that you are helping advance knowledge of the ecosystem and aiding in its protection.
Nurse sharks are usually easy to approach, especially during the day when they are sluggish. They are generally docile but may bite if harassed or cornered. As such, divers and snorkelers should avoid petting or handling nurse sharks
Nurse sharks are active, nocturnal predators that consume a variety of prey. They have jaws specialized for sucking prey out of reef crevices and crushing hard-shelled animals. Nurse sharks also have a number of special feeding techniques in their behavioural arsenal. They often root around in the sand with their snout to uncover buried prey. In order to feed on the thick-shelled queen conch, nurse sharks flip the conch upside down with their snout before sucking out the soft meat. Nurse sharks have also been observed resting patiently in open sandy areas, propping their body up with their pectoral fins. Unsuspecting prey sometimes move under their body, believing it is a shelter, which is when the shark pounces.
Observe, record & share:
O G.GC-101 – Digging: Nurse sharks may root around in the sand to uncover buried prey
O G.GC-102 – Crushing hard prey: Hard-shelled prey like lobsters are sucked up and crushed
O G.GC-103 – Flipping conch: Nurse sharks flip conchs upside down before sucking out the meat inside
OG.GC-104 – False shelter: Nurse sharks prop themselves up on the pectoral fins and pounce on unsuspecting prey that try to shelter there
Attack & Defense Behaviour
Nurse sharks have very few natural predators due mainly to their size which makes them too big for most reef predators to tackle. Only larger shark species are known to prey on nurse sharks. Nurse sharks tend to stay hidden within protective caves and crevices for most of the day. When threatened, nurse sharks escape to shelter and if cornered, or extremely agitated, they may bite.
Observe, record & share:
O G.GC-201 – Hiding: During the day nurse sharks rest under ledges or in caves, sometimes in groups
O G.GC-202 – Escaping: A nurse shark harassed by a larger opponent may escape to the shelter of a familiar ledge or cave where it feels more secure
O G.GC-203 – Biting: A nurse shark attacked by a larger opponent may bite in defence, not an idle threat from a species whose powerful jaws are designed for crushing shells
Nurse sharks reproduce sexually by internal fertilization and do not undergo sex change during reproductive development. During the mating season, male nurse sharks look for females during daylight hours in shallow water. Courtship begins as the two sharks swim side by side, and a receptive female responds by arching her body toward the male. The male grasps one of the female’s pectoral fins in his jaws to anchor himself and then twists his body until the pair’s genitals align and copulation can occur, usually with jerking motions. If a female is not interested in mating, she may spin around to prevent the male from attaching, and may even swim into shallow water or attempt to bury her fins in the sand so that the male cannot get a grip. Individual female nurse sharks are receptive to mating every two years. Mating season generally occurs during the summer, peaking in June and July, and pregnant females give birth to pups in November and December after a 6 month gestation period.
Observe, record & share:
O G.GC-301 – Following: Males follow or swim beside females
O G.GC-302 – Female acceptance: A receptive female arches her body towards the male
O G.GC-303 – Fin biting: Males bite the pectoral fins of a receptive female
O G.GC-304 – Mating: An anchored male aligns genitalia with the female and mates
O G.GC-305 – Unreceptive female: Females who do not want to mate spin to dislodge males, may swim into extremely shallow water or bury their fins in the sand
O G.GC-306 – Pregnancy: Pregnant female sharks have swollen bellies
O G.GC-307 – Birth: Pregnant female sharks give birth to live young in shallow water
False shelter: Nurse sharks are sometimes found lying in open sandy areas, propping themselves up on their pectoral fins. Observations on captive nurse sharks have revealed that sharks achieve this position by alternately rolling side to side while digging the tip of each pectoral fin into the sand. This creates a small dark space underneath the snout which researchers believe is mistaken for a shelter by prey, such as small fish and crabs. When an unsuspecting animal moves into this false shelter, the nurse shark pounces and consumes them.
Did You Know?
• Nurse sharks are ovoviviparous, which means that they produce eggs that develop and hatch inside the body.
• Female nurse sharks can incubate and give birth to up to 40 pups at a time, but most litters are between 20 and 30 pups. Since nurse sharks mate multiple times with different partners, pups in the same brood may be the product of as many as four different fathers!
• Newborn and juvenile nurse sharks grow up in mangroves, where the thick root system provides shelter from large predatory fish. Human coastal development is damaging mangrove forests, resulting in fewer nursery areas for these sharks.
What to do?
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