Nurse Sharks: Characteristics, Behavior, Feeding, Mating, Attacks | Sea Life, Islands and Oceania

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NURSE SHARKS

nurse shark swimming

Nurse sharks (Scientific name: Ginglymostoma cirratum) are one of the most benign and sluggish shark species. Reaching a length of 4.3 meters (14 feet) and a weight of 150 kilograms (330 pounds), they spend much of their time cruising the bottom of the sea near the shore and searching through rocky crevices and caves for prey such as squid, crabs and lobsters. Their name comes from the powerful sucking sound made by their powerful throat muscle, small mouth and large pharynx which in the old days reminded some people who heard it of nursing children. They are also known as cat sharks. They source of the name nurse shark is a matter of debate.

Nurse sharks are one of the most commonly seen sharks on coral and rocky reefs in the western Atlantic Ocean and Caribbean Sea. They are known as easy-going predators and have been described as the “couch potatoes” of the shark world, according to the National Park Service. But don’t underestimate them. The slow-moving bottom dwellers have small mouths but strong jaws filled with thousands of tiny, serrated teeth. Their lifespan in the wild is around 25 years.

Nurse sharks have have few known predators other than humans and other sharks. One 45-centimeter (17-inch) juvenile was found in the stomach of a 2.3-meters (7.5-foot) lemon shark . Two nurse sharks were recorded in the stomach of 2.2-meter (7.2-foot) tiger shark.. Great hammerheads and bull sharks have also been observed attacking nurse sharks on several occasions but failed to injure them. American alligators and American crocodiles occasionally prey on nurse sharks in some coastal areas. [Source: Michael Barbour, Animal Diversity Web (ADW), Wikipedia]

Nurse sharks are utilized by humans for the pet trade and food. Their body parts are sources of valuable materials. They are an ecotourism draw. Nurse sharks are captured for aquariums. They are typically take well to and are docile in captivity. Scientists like them because they are robust, able to admirably tolerate capture, handling, and tagging. The skin is also used for leather. Occasionally nurse sharks are unintentionally caught in fish nets. In the 2000s, The International Union for Conservation of Nature (IUCN) stated the fins and meat were sold at aroun US$1.60 per kilograms (US$ 0.75 per pound.) The IUCN Red List lists nurse sharks as “Near Threatened”. They have no special status according to the Convention on the International Trade in Endangered Species (CITES). They are considered to be a species of least concern in the United States and in The Bahamas, but considered to be near threatened in the western Atlantic Ocean, particularly in South America, many areas of Central America and the Caribbean. In Panama, they are fished for fins and meat. Columbia have several protected areas for them. [Source: Michael Barbour, Animal Diversity Web (ADW) /=]

Websites and Resources: Shark Foundation shark.swiss ; International Shark Attack Files, Florida Museum of Natural History, University of Florida floridamuseum.ufl.edu/shark-attacks ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems

Nurse Shark Habitat and Where They Are Found

nurse shark range

Nurse sharks live in shallow, coasal, saltwater, marine environments in tropical and subtropical climates. You can typically find them in reefs, coastal areas as well as in estuaries at depths of one to 130 meters (3.28 to 426.51 feet). Juvenile nurse sharks are found at depths ranging from one to 4 meters, older juveniles and adults favor from depths of one to 75 meters during the day. At night both juveniles and adults stay between one and 20 meters in depth. Juveniles often hide in crevices in shallow lagoons. Adults are more wide-ranging, inhabiting deeper reefs, around bridges, rocky areas, and boulders. The lowest recorded depth was at 130 meters. This species is not migratory (make seasonal movements between regions, such as between breeding and wintering grounds), and shows strong site fidelity. [Source: Michael Barbour, Animal Diversity Web (ADW) /=]

Nurse sharks are found in inshore areas in the western and eastern Atlantic and the eastern Pacific. In the Pacific live in waters off the coast of Estero de La Bocana, Baja California Sur, in Central America along the Pacific coast, the Gulf of California, and to just south of the coast of Nazca, Peru in South America.

In the eastern Atlantic Ocean, nurse sharks are distributed in the Bay of Biscay between France and Spain near the coast as well as from the Strait of Gibraltar south to Luanda, Angola. In the western Atlantic Ocean, they are found in coastal waters ranging from Portsmouth, New Hampshire to southern Belize. They have also been seen in waters off Cuba, the Bahamas, the Dominican Republic, and Puerto Rico. Nurse sharks in South America are distributed from Guyana to the State of Sao Paulo in Brazail to the south.

Nurse Shark Physical Characteristics

hiding out in the reef

Nurse shark adults range in length from one to three meters (3.5 to 19 feet), with their average length being 1.93 imeters (6.3 feet). They range in weight from 70.5 to 114.5 kilograms (155 to 252 pounds). Both sexes are roughly equal in size and look similar. At birth nurse sharks are 27 to 30 centimeters (10.6 to 12 inches) in length. Among the heaviest nurse sharks are females with with eggs. Castro (2000) examined one female weighing 114.5 kilograms. Reports of large sizes are unconfirmed.[Source: Michael Barbour, Animal Diversity Web (ADW) /=]

Nurse sharks are yellow to grayish-brown in color. Juveniles have small, dark, eye-spot-like spots covering their bodies. Nurse sharks are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature), heterothermic (have a body temperature that fluctuates with the surrounding environment) /=\

Nurse shark have very tough skin and a pair of barbels under their mouths that are used in sensing out the invertebrates that it feeds on. According to Animal Diversity Web: Nurse sharks have five gills located between the head and first dorsal fin. The fifth gill almost overlaps the fourth. The dorsal and second dorsal fins are rounded. The first dorsal fin is 25 percent larger than the second. The anal fins are similar in size to the second dorsal fins and precede the tail. Nurse sharks have nasoral grooves and long barbels that surround the mouth. The eye location is dorsolateral approximately 20 centimeters from the mouth in adults. Between the eyes and gills is a spiracle which is a vestigial gill slit that takes in oxygen from the surrounding water while the shark is stationary. These sharks have 30 to 42 upper teeth and 28 to 34 lower teeth in single rows. /=\

Nurse Shark Behavior

Nurse sharks are nocturnal (active at night), motile (move around as opposed to being stationary), sedentary (remain in the same area), social (associates with others of its species; forms social groups), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). [Source: Michael Barbour, Animal Diversity Web (ADW) /=]

20120518-Nurse_sharks cartagena.jpg
Nurse sharks
Like rays, nurse sharks spend a lot of time just just lying on the sea bottom. They can “walk” along the bottom using their pectoral fins like limbs and sometimes are found in groups with several dozen individuals. They show strong site fidelity (loyalty to a certain reef or placem a trait typical of reef sharks) and hunt at night. According to Animal Diversity Web: They stay in groups and return at dawn to the same location for rest in groups or piles. The social hierarchy may be correlated with the same biting as performed during mating. Nurse sharks use olfaction to find prey. They use the snout to push the mouth against small crevices and suck prey out. There is little data on the migration habits and mating of shivers (pods or schools) of nurse sharks across different sites. Due to the strong site fidelity of the nurse shark, there have been cases of geographic population fragmentation and local extinctions.

Nurse sharks are territorial (defend an area within the home range), and will bite competing sharks for prey. The home range is very limited, sources not listing specific territory sizes. Multiple studies had the same tagged specimen return over the course of multiple years. It often returns from feeding during the night to the same shallow water or cave locations by dawn to rest in groups or piles. Nurse sharks have high territorial (defend an area within the home range), fidelity and do not travel more than several square kilometers from their point of origin. /=\

Nurse Shark Perception and Communication

Nurse sharks communicate with vision, touch, sound, chemicals usually detected by smelling and electric signals and sense using vision, touch, sound, chemicals detected by smelling and electric signals, using sight, sound, electroreception, touch, and smell to detect its surroundings. Sight is limited to 10 meters and used in conjunction with other senses..

in Fish Rock Cave, New South Wales

According to Animal Diversity Web: Nurse sharks do not identify prey with sight. Sound is in the form of an acoustic near and far-field perception . Gardiner et al. (2014) report that the near-field perception can acquire sound pressure signals at distances 0.4 to two body lengths of the nurse shark, while far-field perception can be detected in low frequency signals over multiple kilometers away. This is slightly different than reported by Casper and Mann (2006), who found that the nurse shark's most sensitive hearing is between 300 Hz and 600 Hz which is in the ultra low frequency spectrum. [Source: Michael Barbour, Animal Diversity Web (ADW) /=]

Olfaction, or smell, is used to detect odor plumes of prey. The variables that determine the distance an odor plume is detectable is the source strength, wavelength, and environmental signal-to-noise ratio. Smell is used for prey identification. Gardiner et al. (2014) found that by blocking olfaction, nurse sharks neither detect nor feed on nearby prey. Electroreception is through the ampullae of Lorenzini located in the shark's snout. This electroreception is used for precise directional locating of prey or other creatures. This is used at distances less than one meter.

Nurse Shark Food and Feeding Behavior

Nurse sharks are opportunistic predators and obligate ocean floor feeders. Obligate carnivores, are also called hypercarnivores, have diet that is at least 70 percent meat. Nurse sharks hunt, forage, stalk and ambush prey, mostly at night. They are adapted to suction-feed within three centimeters of their mouth. They often create vacuums with their mouth and suck prey from crevices. They can suck stubborn, hard-to-dislodge prey from the their hiding places into their mouths in a as little as 50 milliseconds.

Nurse sharks feed mostly on fish, rays, cephalopods (most squid and octopus), gastropods, bivalves, sea urchins, and crustaceans but coral pieces and algae have also been found in their stomachs. Castro (2000) brokedown of stomach contents of the nurse sharks he sampled as: Teleostei (fish) — 89.11 percent; Cephalopods — 4.46 percent; Other — 2.48 percent; Crustaceans — 1.98 percent; Anthozoa 1.49 percent, Chondrichthyes 0.50 percent. [Source: Michael Barbour, Animal Diversity Web (ADW)]

Nurse sharks are typically solitary nocturnal hunters and foragers, rifling through bottom sediments and roaming around reefs and rocky areas in search of food. at night, but are often gregarious during the day forming large sedentary groups. Their suction powers are among the highest ever recorded for any aquatic animal. Although their small mouths limit the size of prey, they sometimes employ suck-and-spit behavior or shake their head violently to reduce prey into manageable sizes. [Source: Wikipedia]

Nurse Shark Reproduction

nurse shark mouth

Nurse sharks are ovoviviparous (aplacental viviparous, eggs are hatched within the body of the parent) and iteroparous (offspring are produced in groups such as litters). multiple times in successive annual or seasonal cycles). They engage in internal reproduction in which sperm from the male fertilizes the egg within the female, give birth to live young and produce litters of 20 or 30 pups. [Source: Michael Barbour, Animal Diversity Web (ADW) /=]

Nurse sharks engage in seasonal breeding. Females breed once every other year. Copulation and fertilization occurs in the tw-to-fouur-week breeding season in June and July. The gestation period ranges from five to six months.Females reach sexual or reproductive maturity at 15 to 20 years. Males reach sexual or reproductive maturity at 10 to 15 years.

Nurse sharks are polygynandrous (promiscuous), with both males and females having multiple partners with pups having multiple paternities. . They are one of the few shark species known to exhibit mating site fidelity, as they will return to the same breeding grounds time and time again. They also stay in the same group after copulation.

Mating Nurse Sharks

According to Animal Diversity Web: Male nurse sharks begins mating by nudging the female into position with their head. Often he will bite a pectoral fin or flank in order to hold on. The male then inserts its clasper until sperm transfer is complete. Like other sharks, the purpose of the male's siphon sac is to assist in sperm competition and to flush rival sperm out. The siphon sac is a pair of bladders attached to the claspers of the male that uses seawater to inject its sperm into the cloaca from the clasper. The action of contracting the bladder and force from the seawater flushes competing sperm out of the female nurse shark. This happens just prior to copulation. [Source: Michael Barbour, Animal Diversity Web (ADW) /=]

During copulation, the female nurse shark remains quite motionless. Biting behavior in males has been noted as being a possible indicator of a sexual hierarchy and is maintained through such behavior. Other specific courtship and mating behaviors include the male and female swimming parallel and synchronously side-by-side. If the female is avoiding copulation she will lie on her back, float in the water, or rest motionlessly on the ocean floor. The female might also pivot and roll on her back when a male bites her pectoral fin. If the female is receptive, she will arch her body toward the male, cupping her pelvic fins. /=\

Describing a pair of nurse shark mating off the Florida Keys, Harold L. Pratt Jr. and Jeffrey Carrier wrote in National Geographic, "To subdue his partner, the male must seize the females' pectoral fin, flip her, and carry her from the shallows to deeper water...Suddenly a spray of seawater erupts from the surface — it's the male shark lunging for a female's fin — and a tail slaps the water with a percussive boom." [Source: Harold L. Pratt Jr. and Jeffrey Carrier, National Geographic, May 1995]

"Amid a swirl of fins we watched as the male struggled to arch his body over the female... Often one of his penis-like claspers poked out of the water, pointing skyward." The male then got a tight grip on female's fin and aligns his body with hers. "Thus anchored he can roll the female over, flick his tail underneath her to brace himself, and insert the clasper. Successful copulation lasts between one and two minutes...Afterwards, the male collapsed on the sea bottom. This evident fatigue may result from the fact that the male is deprived of oxygen the whole time he has his jaws clamped onto the female's fin. After days of mating, the female swims away with a chewed up pectoral fin." Less than 10 percent of attempts to mate by nurse sharks end in success.

Nurse Shark Young and Development

Young nurse sharks are born fully developed at about 27 to 30 centimeters (around one foot) long. Litters form a nursery in areas of shallow turtle-grass beds and coral reefs. Carrier and Luer (1990) found that growth rates of young nurse shark averaged about 13 centimeters (one foot) per year, with their weight increasing an average of 2.3 kilograms (five pounds) per year in the wild. Nurse sharks exhibit indeterminate growth (they continue growing throughout their lives), but the rate of growth slows as they get older. [Source: Michael Barbour, Animal Diversity Web (ADW) /=]

Nurse sharks reach sexual maturity at certain lengths depending on sex — 200 to 210 centimeters (6.5 to 7 feet) in length for males, which they reach after 10 to 15 years of age, and 240 and 260 centimeters (8 to 8.5 feet) for females, which they reach after 15 to 20 years.

juvenile nurse shark

Young nurse sharks inherit the territory of their parents, mother or father. Nurse shark parental involvement is limited to juvenile nursery period in their local habitat. According to Animal Diversity Web: Research does not indicate whether or not it is currently known for parents to have specificity towards caring for specific pups.

The promiscuous nature of both sexes and multiple paternity in a litter is likely to attribute to the community raising effort in the nursery. It is not outwardly apparent that there are distinguishing features to identify paternity among the litter. The litter is involved in the social group of the local nurse shark population and as such inherits the local territory.

Nurse Shark Attacks

On some list nurse shark are ranked fourth in documented shark bites on humans, likely due to careless behavior by divers, swimmers and snorkelers who overestimate nurse sharks calm, sedentary disposition. If harassed or cornered nurse sharks will bite but otherwise they generally leave humans alone.

The International Shark Attack Files at the Florida Museum of Natural History only records unprovoked shark attacks on humans. According to its reckoning nurse sharks have accounted for nine non-fatal unprovoked attacks and zero fatal attacks for of total of 9 attacks since 1876, which is not so many especially when one considers how often the fish are enountered . [Source: International Shark Attack Files, Florida Museum of Natural History, 2023]

Several Instagram models have been bitten by nurse sharks while posing for photos with them in the Bahamas. Most wounds are considered relatively minor. In December 2017, honeymooner Sarah Illig was swimming with adult nurse sharks in the Bahamas when she was bitten on the arm. The 25-year-old’s husband filmed the incident, which saw the shark approach from Illig’s left side and nipping her arm. [Source: Tracking Sharks, Kevin McMurray, December 22, 2017]

According to Washington Post” “Knowingly or not, people swim near nurse sharks every day without incident. Attacks on humans are rare but not unknown, and a clamping bite typically results from a diver or fisherman antagonizing the shark with hook, spear, net, or hand. The bite reflex is such that it may be some minutes before a quietly re-immersed nurse shark will relax and release its tormenter. The small teeth seldom penetrate deeply but are razor sharp. Holding still reduces damage to both shark and man. Leaving sharks alone is the best tactic. [Source: Lindsey Bever, Washington Post, May 16, 2016]

In 2017, Tracking Sharks reported: A fisherman got more than he bargained for off the coast of Malaysia. Sairol Harun was wading in the waters off Bagan Lalang Beach in Sepang, when a nurse shark popped up. The shark latched onto the 24-year-old’s left thigh and refused to let go. Harun waded back to shore with the shark still attached to his leg and called police for help. The Malaysian Public Defense Forces (APM) arrived with an ambulance and attempted to remove the shark. “APM team takes about 10 minutes to release the bite of the fish using special equipment,” the JPJ/POLIS said in Facebook post. The man was taken to hospital where he was treated for the minor injury.[Source: Tracking Sharks, Kevin McMurray, December 22, 2017]

Nurse Shark Grab-and- Won’t-Let-Go Attacks in the Florida Keys

Nurse sharks have bitten a number of people who have harassed them or accidentally startled them. When provoked they will attack and often hold on to the victim with unyielding pit-bull-like grip. Describing one such attack in the Florida Keys, WPLG Local10.com reported: A Homestead man ended up with 16 stitches after a nurse shark clamped onto his foot while he was working on a dock. Andres Garcia was in the water in Key Largo when he said the shark bit down and grabbed on. [Source: Ian Margol and Michelle Solomon, WPLG Local10.com October 16, 2020]

Garcia said he isn’t sure if he stepped on the shark or if he just accidentally got too close to the area where the shark had been hovering. His coworkers tried to pry the shark from the man’s foot, but it held on tighter, Garcia said. Garcia eventually had to get out of the water with the shark still attached to his foot until it finally let go. The shark held on to his foot for at least 15 minutes, he said. Garcia said he is fine and recovering from the injuries.

The Florida Marine Patrol said nurse sharks swim slowly and can appear to be harmless, but they can be dangerous and should be avoided. "This is not unusual," said George Burgess, director of the International Shark Attack File. "It is hard to aggravate a nurse shark. They are pretty quiet animals, but if you get them mad, they hold on like a bulldog...In one memorable incident, an off-duty police officer felt obliged to pull out his service revolver and shoot the shark off a victim on a beach in Fort Lauderdale or Miami."

In September 2017, a man was bitten on the stomach by a juvenile nurse shark in the Florida Keys. Video shows the sharks refusing to let go until its gills were sliced open. “An unidentified man was filmed with a 3- to 4-foot long nurse shark attached to his arm. The video, originally shared to TikTock, identifies the location as Jenson Beach, Florida on Aug. 30. In the video, a man is seen walking around with the shark attached to his arm as passerbys offer tips on how to remove the shark. According to the man who posted the video, the shark cradler was taken to the hospital and the shark removed. Although there is no official confirmation about the shark’s fate, it is most likely dead. Witnesses in the video say the man was swimming when the shark latched onto his arm. [Source: Kevin McMurray, Tracking Sharks, September 2, 2020]

Ervin McCarty had a similar encounter in 2017 that was caught on video. McCarty was snorkeling Sept. 2 off Marathon City in the Florida Keys with several friends. One person in the group shot a grouper which was lodged in an underwater hole. When McCarty swam down to remove the grouper, a small nurse shark bit and latched on to his abdomen. Although he struggled to remove the shark, it did not release its bite. Eventually the group used a knife to slice into the shark’s gills, even though the shark continued to hold on. The shark finally let go after it was eviscerated but then bit McCarty one last time.

People Admitted to Hospitals with Nurse Sharks Attached to Them

In 1998, a 16-year-old Illinois boy was bitten by a nurse shark off Marathon Key in the Florida Keys after he grabbed the shark's tail. The unrelenting shark wouldn't let go of the boy's chest, and stayed attached to the boy until he reached a hospital where doctors cut the animal's spine to kill it. The boy was scuba diving with his father near Marathon, when he saw a three-foot nurse shark swimming near him and grabbed its tail, emergency workers said. The shark bit his chest and wouldn’t let go. Burgess doesn't count such incident in his statistics, he said, because it was a provoked attack. The child taunted the animal. He puts that one in a different file, he said: “S for Stupid.'' [Source: Reuters]

In May 2016 , an unidentified 23-year-old woman was bitten on the right forearm by a small 60-centimeter (two-foot) -long nurse shark while swimming near the south end of Red Reef Park in Boca Raton, Florida. She was taken to the hospital with the shark still attached to her arm. Witness said they saw the woman’s friends harassing the shark and grabbing its tail.[Source: Lindsey Bever, Washington Post, May 16, 2016]

The South Florida Sun-Sentinel reported that the 2-foot shark latched onto the woman’s forearm and refused to release her — even as it was dying. “The shark wouldn’t give up,” Boca Raton resident Shlomo Jacob, who witnessed the scene, told the newspaper. “It was barely breathing but it wasn’t letting go of her arm, like it was stuck to her or something.”

According to the Washington Post: Witnesses said the woman emerged from the water in Boca Raton with the shark hanging from her arm; a man supported it as paramedics made their way to the scene, according to news reports.By the time they arrived, a bystander may have killed the small shark, according to the Palm Beach Post.Ocean Rescue Capt. Clint Tracy told the Sun-Sentinel that medical personnel used a splint board to hold the woman’s arm and the shark was put on the stretcher with her to take her to the hospital. I have never seen anything like it,” Tracy told the newspaper. “Never even heard of anything like this.” The woman was listed in stable condition. Tracy, the Ocean Rescue captain, told the Sun-Sentinel that some swimmers had been antagonizing the small shark, though he did not know whether the woman played a part in it. An 11-year-old told the paper that people had been “messing with it” — holding the shark up by its tail.

Jim Abernathy, a local shark expert who gives dive tours along the coast, told ABC affiliate WPBF that he believes the nurse shark was fighting back when it bit the woman “I’m 99 percent sure that the person grabbed on its tail, and because the shark is only that big, it turned around and bit her right on the arm,” he told the news station, adding: “The sad thing about all of this is the shark was minding its own business, got taken to a hospital [and] will be killed because someone pulled its tail.”

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023