Nurse Shark

Maximum longevity: 25 years (wild)

Nurse sharks range in length from about 75 centimeters for the short tail nurse shark to 4 meters in length for the other types of nurse sharks. The average weight of a 240 centimeter long nurse shark is 330 pounds. They are generally dark in color or have dark scattered spots along their bodies. They have broad heads, no grooves around the outer edge of their nostrils, and relatively fat or stout bodies and tails. Their anal fins are slightly behind their second dorsal fins and just in front of their caudal fins. Anal fins are absent in some families of sharks.

Other Physical Features: bilateral symmetry

Average mass: 60280 g.

Average lifespan
Status: wild: 25.0 years.

Nurse sharks live off of sandy beaches, mud and sand flats, and from the intertidal zone on coral and rocky reefs to depths of 70 meters.

Aquatic Biomes: benthic ; reef ; coastal

Nurse sharks live in warm waters. They range from the Eastern Pacific Ocean, Eastern and Western Atlantic Ocean to the Indian Ocean.

Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )

Nurse sharks eat a variety of foods. Their diet includes small fishes, shrimps, octopus, sea snails, crabs, lobsters, squid, sea urchin, and corals.

Nurse sharks are used in several fishing industries for bait to catch other aquatic animals. They also help control populations of several sea creatures. Scientists are also interested in these sharks because they are easy to find because of their dark color and slow moving nature. Their dark color makes them easier to spot in the water and their slow locomotion makes it easy to catch and tag these sharks, making them a relatively easy anmial to study.

At present, Nurse sharks have no special conservation status. They are sought out for crab trap bait and for sport fishing, however, and their reproductive rate is relatively slow. This suggests that their populations bear watching.

IUCN Red List of Threatened Species: near threatened

Nurse sharks are interesting animals for of several reasons. It is not true that that all sharks need to swim in order to breath, and when they cannot for whatever reason, they die. Sharks breath primarily by using a ram-jet ventilation system, which requires that they be swimming. Some sharks, however, have a second system based on respiratory pumping of water. Nurse sharks can switch to this respiratory system when they are at rest, saving energy and the neccesity to swim to get plenty of water over their gills. This is especially important for bottom dwellers such as Nurse sharks. Nurse sharks do not attack humans, despite claims to the contrary; they are one of the most docile animals in the sea.

Very little is known about most shark mating rituals, and the same holds true for the Nurse shark. The Atlantic Nurse shark has been observed mating on the ocean floor. In general, the male inseminates the female with his claspers (these are located between the male's pelvic fins). During mating he turns his claspers foward and inserts one into the female and transfers his sperm. Nurse sharks can be either oviparous or ovoviparous. In oviparous organisms the eggs develop and hatch on the outside of the body. The pups, as baby sharks are called, hatch out of a leathery protective covering with the yolk attached and stay on the ocean floor until they fully mature. In ovoviparous creatures the eggs develop on the inside of the body and hatch within or immediately after extrusion by the parent. The yolk of these pups are hatched inside the uterus before the pups are developed, and they too have leathery eggs. These sharks have from 20-30 pups at a time. Nurse sharks grow about 13 centimeters in length and 2-3 kilograms a year. They do not reach sexually maturity until they are from 15 to 20 years old.

During the day the nurse shark is a sluggish animal, spending most of its time resting on sandy bottoms, or in crevices in rocks and coral reefs. Often several nurse sharks may congregate when resting, sometimes even piling on top of one another (2). At night however, the nurse shark actively roams the sea bottom and reef for prey. It feeds on bottom invertebrates such as spiny lobsters, shrimps, crabs, sea urchins, squid and octopi (2). It is also feeds on fish, its nocturnal nature enabling it to prey on resting fish that would be too active during the day to capture (2). The nurse shark's small mouth and large pharynx enable it to feed by a unique suction method, effectively making the nurse shark the 'hoover' of the ocean floor. By cupping its mouth over a hole or crevice and expanding its throat, it creates a vacuum that sucks prey out of their hiding (4). This suction-feeding is also useful for extracting snails from their shells (2), and it will dig in sand to root out prey sensed by its fleshy barbels (2). The nurse shark is one of few sharks in which courtship behaviour is relatively well known (4). The male swims alongside the female, grabs one of the pectoral fins in his mouth, rolls her over and they mate (4). A large number of males will often try to mate with a single female, and females often bear numerous bite-scars and bruises received during mating attempts. It is therefore not surprising that females frequently try to avoid males by swimming in very shallow water, where they can bury their pectoral fins in the sand (5). Nurse sharks are ovoviviparous (2), a method of reproduction whereby the young develop inside a weakly-formed egg shell within the mother, receiving nourishment from their yolk sac, for five to six months (2). The females move to shallow seagrass beds and coral reefs to give birth to 20 to 30 pups in late spring and summer (2). Like many sharks the nurse shark is slow growing, with males not reaching maturity until 10 to 15 years of age, and females 15 to 20 years (2).

The nurse shark is included as a Vulnerable species in the Official List of Endangered Animals in Brazil, fisheries are managed within United States' waters, and the Colombian government is considering a ban on the nurse shark fishery along with an extensive habitat protection campaign (1). However, in regions outside of the Western Atlantic, the lack of data makes it difficult to assess the status of populations, and subsequently to implement appropriate conservation measures. Measures recommended include the regulation of spear-fishing and the marine ornamental fish trade, compulsory release of incidentally caught sharks, and the establishment of no-fishing areas encompassing mating and breeding grounds (1). Countries should be motivated to take action to prevent over-fishing of the nurse shark as it is likely to be far more valuable alive for dive-tourism than as fisheries products (6).

The strange looking nurse shark is not the heavy, fearsome fish we normally expect a shark to look like. Its long, flexible body is yellowish-brown to grey-brown, with two spineless, rounded dorsal fins and a long tail fin that can be over a quarter of the whole body length (2). The large, rounded pectoral fins are flexible and muscular, and can be used as limbs to clamber along the sea bottom (2). The head is broad and flat, with small jaws housing small teeth (3) and fleshy, sensory projections (barbels) hang down by its mouth (2). It is not entirely clear where the nurse shark got its strange name from, perhaps from the ancient English name for a dogfish, 'huss' (4). More suitable is its scientific name which translates in Latin as 'the shark with the flexible curly mouth' (4).

The nurse shark inhabits inshore tropical and subtropical waters, where it is found at depths of less than one meter down to 130 metres (2). It is frequently found on rocky and coral reefs, and in channels between mangroves keys and sand flats (2).

Occurs in the Western Atlantic, from Rhode Island in the United States to southern Brazil; the Eastern Atlantic, from the Cape Verde islands to Gabon; and the Eastern Pacific, from the Gulf of California to Peru (2).

Classified as Data Deficient (DD) by the IUCN Red List. The Western Atlantic subpopulation is classified as Near Threatened (NT) (1).

Nurse sharks are commonly caught in small-scale local fisheries in some parts of its range, and are incidentally captured in many coastal fisheries (1) (2). Its tough, thick hide makes good leather, the flesh is consumed by humans and used for fishmeal, and oil is extracted from the liver (2). The nurse shark is also captured for the aquarium trade, and is occasionally the target of spear fishermen (1). As the nurse shark grows slowly and matures late, this exploitation can cause populations to decline rapidly and recover slowly (6). The threat of overexploitation is compounded by the impact of humans on the coastal and reef habitats of the nurse shark (1) (6). Coral reefs are a particularly vulnerable habitat, being impacted by pollution, sedimentation, global climate change and disturbance from tourism (1). Extreme population reductions have already been recorded in the southern Western Atlantic, and it is possible that the nurse shark is declining, unnoticed, in other areas where there is a lack of data (1). For this reason, the World Conservation Union (IUCN) has classified the nurse shark as Data Deficient (1).

This shark is commonly captured in local artisanal fisheries in some areas where it occurs, particularly the tropical western Atlantic. It was, however, rare in a localized broad-spectrum fishery out of Guaymas, Mexico (examined by the writer in 1974). It has been prized for its extremely tough, thick, armour-like hide, which makes an exceptionally good leather, but is also used fresh and salted for human consumption, as well as for liver oil and fish meal. The stratoconidia (earstones) of this shark and other species are said to be used as a diuretic by local fishermen in southern Brazil.It is easily captured with line gear, gill nets, fixed bottom nets and bottom trawls, and spears. It can be readily captured on sportsfishing tackle, but is generally regarded as being too sluggish to be much of a game fish (unlike the tawny nurse shark in Australia). Divers have sometimes speared nurse sharks, which is inane 'sport' because of its senselessness. The sharks are often sitting ducks for spearfishing divers on the bottom, and the modest speed of these sharks even when active make them no great challenge to hit. However, the toughness of these sharks may make them difficult to subdue underwater, and a diver that spears one may receive a well-deserved bite. The nurse shark was regarded as a pest by fishermen in the Lesser Antilles because it rifled fish traps for food. Conservation Status : The conservation status of the nurse shark needs to be assessed throughout its range, but particularly offWest Africa, parts of the tropical western Atlantic and in the eastern Pacific where intensive inshore fisheries are being pursued and the distribution and abundance of these sharks is sketchily known. They are regarded as particularly vulnerable to overexploitation because of their slow growth, low reproductive rate, inshore habitat, apparent site-specificity, their presence in areas with intense inshore fisheries, and very little catch data available. The USAwas the only country reporting nurse shark catches (214 t in 1995) to FAO over the vast range of this shark, and this was only reported during the last decade. Apart from their vulnerability to inshore fisheries, these sharks have been increasingly captured for private and public aquaria, and may have declined in some areas as a result of exploitation. Carrier (1996) and Carrier and Pratt (1998) suggested that public entry should be banned during the late spring and summer at one nurse shark breeding site in the Dry Tortugas National Park, Florida Keys, to avoid disturbing the mating of the sharks in shallow water. These sharks are a major asset to ecotourism in the Caribbean, and probably generate far more revenue there as live sharks viewed by divers than as fisheries products.

This is an inshore bottom shark of the continental and insular shelves in tropical and subtropical waters,often occurring at depths of 1 m or less in the intertidal, but down to at least 12 m and off Brazil between 40 and 130 m. The nurse shark is often found on rocky and coral reefs, in channels between mangrove keys and on sand flats. This is a large nocturnal and facultatively social shark that is proverbially sluggish during the daytime but strong-swimming and active at night; it rests on sandy bottom or in caves and crevices in rocks and coral reefs in shallow water during the day, often in schools or aggregates of three to three dozen individuals that are close to, or even piled on one another while resting. Swimming speed was measured at 31 to 78 cm/sec for a 250 cm captive individual (Hussain, 1991). In addition to swimming near the bottom or well off it, the nurse shark can clamber on the bottom using its flexible, muscular pectoral fins as limbs. Preliminary studies suggest that the nurse shark shows a strong preference for certain day-resting sites, and repeatedly homes back to the same caves and crevices after a night's activity. Nurse sharks fitted with conventional and sonic tags show little if any local movement, but adults have a larger range than young (Carrier, 1990). This suggests that groups of these animals are site-localized and vulnerable to local extirpation from overexploitation. This shark has been historically common or abundant in some areas where it occurs, particularly in the tropical western North Atlantic and off Tropical West Africa. Courtship and copulatory behaviour has been observed in captivity (Klimley, 1980) and studied in detail in the wild (Carrier, Pratt and Martin, 1994), and is apparently rather complex. In captivity a pair or sometimes a triplet of adults engage in synchronized parallel swimming, with the male abreast or slightly behind and below the female, but with sides nearly touching. A pair may rest on the bottom on their bellies in parallel after bouts of parallel swimming. While parallel-swimming, the male may grab one of the female's pectoral fins with his mouth, which in turn may induce the female to pivot 90° and roll on her back on the bottom. The male then nudges the female into a position parallel to him, swims on top of the female in parallel, inserts a single clasper in her vent, and then rolls on his back to lie motionless besides the inverted female with clasper still inserted. Carrier, Pratt and Martin divided nurse shark mating into five stages based on field observations of free-ranging individuals in a mating area in the Dry Tortugas, Florida: Precoupling, in which a male or group of males approached a female that was resting or swimming, in the latter case with parallel or tandem swimming, and with males approaching alongside and slightly behind the female with heads close to her pectoral fins. Coupling, in which the male grabs the female's pectoral fin, sometimes with two males grabbing both pectoral fins and with other males circling in close proximity. Positioning, in which the male, or two males, roll the female onto her back, and with the male rolling and aligning his tail and pelvic fins prior to copulation. Insertion and copulation, in which the male copulates with the female, inserting his right clasper if holding her right pectoral, and his left clasper if holding her left pectoral, and thrusts against the female who remains quiescent. Postcopulation, in which the male removes his claspers, releases the female's pectoral, and either the two depart or lie on the bottom in parallel with ventral surfaces down. Over half the copulatory bouts involved more than one male, with a few insertions and copulations involving two or more males. Reproduction is ovoviviparous, with intrauterine development of young being sustained primarily by the large supply of yolk in their yolk-sacs. Young are common in late spring and summer in waters off Florida, when females give birth. Numbers of intrauterine eggs or young are 20 to 30 in a litter. The gestation period is about five to six months and it reproduces every other year. Nursery areas are in shallow turtle-grass beds and on shallow coral reefs. Nurse sharks are slow-growing, with free-ranging tagged juveniles (average about 126 cm long) growing at about 13 cm per year. Males may be 10 to 15 years old at maturity and females 15 to 20 years old (Carrier, 1990; Carrier and Luer, 1990). The nurse shark feeds heavily on bottom invertebrates such as spiny lobsters, shrimps, crabs, sea urchins, squid, octopus, marine snails and bivalves, and also fish including herring (Clupeidae), sea catfish (Ariidae), mullet (Mugilidae), parrotfish (Scaridae), surgeonfish (Acanthuridae), puffers (Tetraodontidae), and stingrays (Dasyatidae). Algae is occasionally found in its stomach and may be sucked in along with prey animals. Its small mouth and large, bellows-like pharynx allow it to suck in food items at high speed. This powerful suction feeding mechanism and its nocturnal activity pattern may allow the nurse shark to take small, active prey like bony fishes that are resting at night but would be too active and manoeuvrable for this big, lumbering shark to capture in the daytime. When dealing with big, heavy-shelled conchs the nurse shark flips them over and extracts the snail from its shell, presumably by grabbing its body with its teeth and by suction. It will dig under coral detritus and in sand with its head to root out prey. Young nurse sharks have been observed resting with their snouts pointed upward and their bodies supported off the bottom on their pectoral fins; this has been interpreted as possibly providing a false shelter for crabs and small fishes that the shark then ambushes and eats. In captivity the nurse shark, when stimulated by food in the form of cut fish, will cruise in circles close to the bottom searching for the food, with its barbels touching or nearly touching the bottom; when it contacts a chunk of food, it may overshoot it but then quickly backs up and rapidly sucks it in. It may even work over vertical surfaces with its barbels.

Maximum said to be 430 cm long but most adults are under 3 m long and the largest reliably reported were 280 to 304 cm. Newborn young are about 27 to 30 cm. Males mature at about 210 cm and adult males reach at least 257 cm; females are immature at 225 to 235 cm and mature mostly at about 230 to 240 cm (though one adult female 152 cm long has been reported) and reach over 259 cm.

Western Atlantic: Rhode Island to southern Brazil, including United States (exceptionally Rhode Island and North Carolina, South Georgia and Florida and Gulf coast from Florida to Texas), Mexico (Gulf of Mexico and Caribbean coasts), Bermuda, Bahamas, Turks and Caicos Islands, Cuba, Puerto Rico, Haiti, the Lesser Antilles, Belize, Jamaica, Barbados, Trinidad, French Guiana, Guyana, Panama, and Brazil (south to Rio de Janeiro). Eastern Atlantic: Cape Verde Islands, Senegal, Cameroon to Gabon, and rarely north to Gulf of Gascony, France. Eastern Pacific: Mexico (Baja California Sur, Gulf of California) south to Costa Rica, Panama, Ecuador, and Peru. The known distribution of the nurse shark suggests at least three geographically isolated populations (eastern Pacific, western Atlantic and eastern Atlantic), but their differentiation, if any, has yet to be studied.

fieldmarks: Moderately long barbels, nasoral grooves present but no circumnarial grooves; eyes dorsolateral, mouth well in front of eyes, spiracles minute; precaudal tail shorter than head and body; two spineless, broadly rounded, dorsal fins and an anal fin, first dorsal fin much larger than second dorsal and anal fins, caudal fin moderately long, over one-fourth of total length; colour yellow-brown to grey-brown, young with small dark, light-ringed ocellar spots and obscure dorsal saddle markings, adults and subadults without spots or saddles. Head in dorsal or ventral view broadly arcuate in young, narrower and U-shaped in adults. Snout bluntly wedge-shaped in lateral view, short and with mouth width about 2.3 to 2.6 times preoral length. Eyes small but usually over 1% of total length, positioned dorsolateral on head and with strong subocular ridges below them. Eyes with ventral edges just above level of dorsal ends of gill slits. Gill openings dorsolaterally situated on head and not or hardly visible from below but just reaching horizontal head rim in dorsal view. Nostrils nearly terminal on snout. Nasal barbels moderately elongated, tapered, slender and over 1% of total length, reaching past mouth. Lower lip trilobate and divided by shallow orolabial grooves connecting mouth with lower labial furrows. Distance between lower labial furrows about 1.5 times their length. Tooth rows 30 to 42/28 to 34, functional tooth series at least 7 to 9/8 to 12. Teeth moderately compressed, not imbricated but in alternate overlap pattern, functional series not separated from replacement series by toothless space. Tooth crown feet broad, cusps moderately tall, cusplets moderately large and 2 to 6 on each side, basal ledges moderately broad. Teeth osteodont, with pulp cavity filled by osteodentine. Body semifusiform. Lateral trunk denticles broad and rhomboid in adults, with three strong parallel ridges and a very short, blunt cusp. Pectoral fins broad and rounded-angular in young and semifalcate in large specimens, apices rounded. Pectoral-fin origins slightly behind to slightly in front of third gill slits. Pectoral fins plesodic and with radials reaching about 80% into fin web, radial segments 7 or 8 in longest radials. Pelvic fins rounded in young, possibly subangular in adults. Dorsal fins apically rounded. First dorsal-fin origin about over, slightly in front, or slightly behind pelvic-fin origins. Second dorsal fin distinctly smaller than first dorsal fin. Anal fin distinctly smaller than second dorsal fin, apically rounded. Anal-fin origin about opposite, slightly behind, or slightly in front of midbase of second dorsal-fin, with apex about under anal-fin base and posterior margin extending behind level of lower caudal-fin origin. Caudal fin long with dorsal caudal-fin margin over 25% of total length (adults). Caudal fin narrow and shallow with dorsal caudal-fin margin 3.2 to 3.6 times caudal-fin depth; no ventral caudal-fin lobe in young but a weak one in adults; preventral caudal-fin margin much shorter than postventral margin and 43 to 67% of it; terminal lobe short and 15 to 19% of dorsal caudal-fin margin. Total vertebral count 168 to 175, monospondylous precaudal count 48 to 50, diplospondylous caudal count 73 to 83 and 43 to 48% of total count. Jaws broadly arcuate. Intestinal valve count 16 to 17. Yellowish to grey-brown above and light whitish brown below, young with small dark, light-ringed ocellar spots and obscure dorsal saddle markings, adults and subadults without spots or saddles.

Dorsal spines (total): 0

Common over shallow sand flats, in channels, and around coral reefs; Young may be found among prop roots of red mangroves (Ref. 26938). Found on continental and insular shelves. A solitary (Ref. 26340) and sluggish fish, often encountered lying on the bottom (Ref. 9987). Macro-carnivore (Ref. 126840). Nocturnal, feeding on bottom invertebrates such as spiny lobsters, shrimps, crabs, sea urchins, squids, octopi, snails and bivalves, and fishes like catfishes, mullets, puffers and stingrays. Algae is occasionally found in its stomach. This species feeds by sucking in food at high speed through its small mouth and large, bellows-like pharynx. It feeds on big, heavy-shelled conchs by flipping them over and extracting the snail from its shell, presumably with its teeth and by suction. Carnivore (Ref. 57616).

Ovoviviparous, with 21 to 28 young in a litter. Development of young in the uterus being sustained by a large supply of yolk. Females give birth in late spring and summer in waters off Florida. During courtship, a pair sometimes a triplet of adults engaged in synchronized parallel swimming. While on it, the male may grab one of the female's pectoral fins with his mouth which induces the female to pivot 90° and roll on her back on the bottom. Then the male inserts a clasper in her vent, and then roll on his back beside the female. Pair may break apart and depart rapidly after copulation or the male may remain motionless on the subtrate as if recovering from the mating bout (Ref. 49562). Not all attempts of males to copulate with a female nurse shark result in successful fertilization, females may employ avoidance by 'pivotting and rolling' to escape from male attention (Ref. 49562). Or females may 'lie on back' and rest motionless and rigidly on the substrate (Ref. 51113, 49562). On the contrary, females send signals of readiness to copulate with males by arching their body toward their male partner and cupping the pelvic fin (Ref. 51126, 49562). Male nurse sharks may mate with many females over several weeks (polygyny) and vice versa (polyandry) (Ref. 49562). Also Ref. 205.

Moderately long barbels, nasoral grooves present but no perinasal grooves, mouth well in front of eyes, spiracles minute, precaudal tail shorter than head and body, dorsal fins broadly rounded (the first much larger than the second and anal fins), caudal fin moderately long, over 1/4 of total length, yellow-brown to grey-brown in color, with or without small dark spots and obscure dorsal saddle markings (Ref. 247). Head blunt, mouth inferior, pair of conspicuous barbels between nostrils (Ref. 26938).

Found on continental and insular shelves. Solitary (Ref. 26340) and sluggish fish, often encountered lying on the bottom (Ref. 9987). Nocturnal, feeding on bottom invertebrates such as spiny lobsters, shrimps, crabs, sea urchins, squids, octopi, snails and bivalves, and fishes like catfishes, mullets, puffers and stingrays. Ovoviviparous with 21 to 28 young in a litter (Ref. 9987, 43278). Kept in captivity for researches. May attack humans if they are molested or stepped upon accidentally. Edible, but mainly valued for its hide, which makes extremely tough and durable leather (Ref. 9987). Common over shallow sand flats, in channels, and around coral reefs; young may be found among prop roots of red mangroves (Ref. 26938).

fisheries: minor commercial; aquarium: public aquariums; price category: medium; price reliability: reliable: based on ex-vessel price for this species

The nurse shark (Ginglymostoma cirratum) is an elasmobranch fish in the family Ginglymostomatidae. The conservation status of the nurse shark is globally assessed as Vulnerable in the IUCN List of Threatened Species. 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 because of their vulnerable status in South America and reported threats throughout many areas of Central America and the Caribbean. They are directly targeted in some fisheries and considered by-catch in others.

Nurse sharks are an important species for shark research. They are robust and able to tolerate capture, handling, and tagging extremely well. As inoffensive as nurse sharks may appear, they are ranked fourth in documented shark bites on humans, likely due to incautious behavior by divers on account of the nurse shark's calm, sedentary nature.

Western Atlantic: Rhode Island, USA to southern Brazil, including the Gulf of Mexico and Carribean, Antilles

benthic