Author: (Bonnaterre, 1788)
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, 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 1/4 of total length, colour yellow-brown to greybrown, with or without small dark spots and obscure dorsal saddle markings.
Nasal barbels moderately long, reaching mouth; tooth crowns rather broad, cusps small and short and cusplets numerous and large. Origin of first dorsal fin about
over pelvic origins; first dorsal fin larger than second dorsal and anal fins; caudal fin moderately long, over 1/4 of total length.
Western Atlantic: Rhode Island to southern Brazil, including Gulf of Mexico, Bermuda, Bahamas, Cuba, Jamaica, Caribbean. Eastern Atlantic: Cape Verde Islands, Senegal, Cameroon to Gabon, and accidental to Gulf of Gascony, France. Eastern Pacific: Southern Baja California, Gulf of California to Peru.
Habitat and Biology:
A common large inshore bottom shark of the continental and insular shelves in tropical and subtropical waters, often occurring at depths of a metre or less in the intertidal, but down to at least 12 m. The nurse shark is often found on rocky reefs, in channels between mangrove keys and on sand flats. This is a nocturnal shark that is proverbially sluggish during the daytime but strongswimming and active at night; it rests on sandy bottom or in caves and crevices in rocks in shallow water during the day, often in schools or aggregates of 3 to three dozen individuals that are close to or even piled on one another while resting. In solrlitinn tn swimmino 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 indicate 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.
Courtship and copulatory behaviour has been observed, and is apparently rather complex. 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 degrees and roll on her back on the boftom. 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.
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 21 to 28 in a litter.
The nurse shark feeds heavily on bottom invertebrates such as spiny lobsters, shrimps, crabs, sea urchins, squids, octopuses, marine snails and bivalves, and also fishes including sea catfishes, mullets, puffers and stingrays. Algae is occasionally found in its stomach. 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 fishes that are resting at night but would be too active 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 with its teeth and by suction.
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 inhales it in. It may even work over vertical surfaces with its barbels.
The nurse shark is often regarded as harmless to people, because of its sluggishness during the day and relatively small teeth. In the Caribbean and off Florida people frequently come in contact with it, and it mostly will not react aggressively when approached but usually swims away when disturbed. However, there have been a small number of non-fatal, unprovoked attacks on swimmers and divers with uncertain motivation on the part of the sharks, though non-feeding aggression or some other motivation is more likely than feeding attacks because of the relatively small prey taken by this shark. In one bizarre unprovoked attack a large nurse shark grabbed a diver's chest with its teeth, then appeared to hold onto his body with its pectoral fins; unfortunately the sex of the shark was not recorded. More commonly people attempt to ride, spear, drag or otherwise harass this shark, or accidentally step on one while wading, and get bitten as a result. Although its teeth are small, the jaws and associated muscles of the nurse shark are extremely powerful and vice-like; in some instances nurse sharks have bitten people and held on, and had to be pried loose with a tool.
These sharks are very hardy and capable of surviving a wide range of temperatures and dissolved oxygen levels in captivity. They grow to adult size when obtained as young and kept in aquaria of sufficient size, and will even give birth in captivity. Specimens have been kept for 24 to 25 years. The young makeinteresting pets and can be trained to feed at the surface. These sharks have often been used for experimental behavioural and physiological research in captivity, for which they are excellent subjects because of their hardiness and ability to learn.
Maximum total length said to be 430 cm but most adults are under 3 m long and the largest otherwise reported were 280 to 304 cm; adults males mature at about 225 cm and reach at least 257 cm; females are immature at 225 to 235 cm and mostly mature at about 230 to 240 cm (though one 152 cm long has been reported) and reach over 259 cm; newborn young about 27 to 30 cm.
Interest to Fisheries:
Very common in shallow waters where it occurs, and often captured in local artisanal fisheries. It has been prized for its extremely tough, thick, armor-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 fishmeal. 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 captured with line gear, gillnets, fixed bottom nets and bottom trawls, and spears. It can be readily captured on sportfishing tackle, but is regarded as too sluggish to be much of a game fish. Divers sometimes spear nurse sharks, which is minimal sport because of their modest speed even when active; but the toughness of these sharks may make then difficult to subdue underwater. In the Lesser Antilles, the nurse shark is regarded as a pest by fishermen because it rifles fish traps for fond.
Lectotype: Museum National d'Histoire Naturelle, Paris, MNHN A.7654, 458 mm female, locality uncertain. Type Locality: American seas.