Orectolobiformes

(Carpet sharks)

Class Chondrichthyes

Order Orectolobiformes

Number of families 7

Evolution and systematics

The exact origin of this group is unclear. The Orectobiformes have a Jurassic record and show relationships to the Hybodontiformes, Squatiniformes, and Squaliformes, with such common characters as a flange on the teeth and nasal barbels.

The order Orectolobiformes comprises seven families: the Rhincodontidae (whale shark), the Stegostomatidae (zebra shark), the Orectolobidae (the wobbegongs), the Ginglymostomatidae (the nurse sharks), the Parascyllidae (the collared carpet sharks), the Brachaeluridae (the blind sharks), and the Hemiscyllidae (the longtail carpet sharks).

Physical characteristics

The Orectolobiformes are small to very large sharks with prominent nasoral grooves (grooves connecting the nostrils to the mouth), nasal barbels, two dorsal fins, an anal fin, and small terminal or subterminal mouths.

Distribution

The Orectolobiformes are mainly an Indo-Pacific species. Only two species are found in other oceans. The nurse shark (Ginglymostoma cirratum) is found in both the Pacific and Atlantic Oceans. The whale shark has worldwide distribution.

Habitat

With a few exceptions, most of the species of the order are found in the shallow waters of the continental shelves. They often are bottom dwellers in rocky areas or coral reefs. The whale shark is the only pelagic species in the order.

Behavior

Most orectolobiformes are sluggish bottom-dwelling sharks that hide among the bottom rocks or coral heads during the day. Almost nothing is known about the behavior of most species.

Feeding ecology and diet

Most of the orectolobiformes are small, sluggish sharks that feed on small invertebrates and fishes. The whale shark, the largest fish in the world, with a maximum length of 39 ft (12 m), feeds on plankton. Little information exists on creatures that are predatory towards fishes in this order, but carcharhinid sharks are known to prey on small orectolobiformes.

Reproductive biology

Both oviparous and viviparous species have been reported. Little is known about the reproductive processes of most orectolobiformes. The reproductive processes of the nurse shark are probably the best known (see species account following).

Conservation status

Most species in the order are not threatened by fisheries. Recently, there have been localized fisheries for whale sharks in the Philippines, India, and Taiwan. There are no fisheries for them in the Atlantic. The whale shark has been protected in several countries, primarily on aesthetic grounds. Two species are listed on the IUCN Red List: the blue-gray carpet shark (Heteroscyllium colcloughi) and the whale shark (Rhincodon typus). Both are categorized as Vulnerable. In addition, the whale shark was added to CITES Appendix II in December 2002.

Significance to humans

Most Orectolobiformes have little, if any, commercial importance. Some species are found in the aquarium trade. The nurse shark has been used for its liver oil, hides, and meat. Nurse shark liver oil was used for various purposes in the past. In Jamaica, the nurse shark was fished solely for its liver, which was used in burning; a fish yielded about a gallon of

oil. In the Florida sponge fisheries of the 1880s, fishermen used nurse shark liver oil to calm the water surface so that they could scan the bottom continuously. A teaspoon of oil was said to produce a smooth surface for as long as a small boat of fishermen worked in one spot. People in Key West killed nurse sharks in summer and extracted the oil, which, at the time, sold for one dollar per gallon.

The hides of the nurse shark were the most valuables hides in the Florida shark fishery of the 1940s. Nurse shark hides were bought by the shark leather industry at prices about 25% higher than those of other species. The price of a 90-in (230 cm) hide was about $3.10 in 1943. At present, nurse sharks are little utilized in Florida. Some nurse sharks are fished for crab bait. The fins are worthless in today's industries.

Although the nurse shark is edible, its meat is very seldom found in Florida markets at this time. This limited utilization affords little protection to the species—many shark fishermen kill nurse sharks caught in their longlines, because they consider them a nuisance species that takes baits intended for other species. The species is included in the Fishery Management Plan for Sharks of the Atlantic Ocean, which has regulated the shark fisheries of the East Coast of the United States since 1993. The ability of the nurse shark to survive in confinement and its hardiness have made it the most popular aquarium and laboratory shark. It is certainly the most commonly displayed shark in aquaria throughout the Americas.

Species accounts

List of Species

Nurse shark

Ginglymostoma cirratum

family

Ginglymostomatidae

taxonomy

Ginglymostoma cirratum Bonaterre, 1788, type locality not specified.

other common names

None known.

physical characteristics

Recognized by its conspicuous, long nasal barbels on the anterior margins of the nostrils and first dorsal fin originating over or posterior to the pelvic fin origin. Very wide head that gives it a tadpole appearance from above. Mouth is full of minute teeth, which are similar in both jaws. Teeth have one large cusp flanked on each side by two or three cusplets. Coloration ranges from rich yellowish to grayish-brown, with most specimens being reddish-brown. Yellow and even white specimens have been reported. Newborn nurse sharks have small black spots over the entire body, with an area of lighter pigmentation surrounding each spot and with bands of lighter and darker pigmentation alternating along the dorsal surfaces. The spots disappear by the time the specimens reach 20 in (50 cm) in length. Capable of limited color changes according to light intensity. Although the size and weight attained by the nurse shark often have been exaggerated in both the scientific and popular literatures, no specimen measured by researchers has exceeded 110 in (280 cm) in length. The largest specimen measured and weighed by Castro in Florida was 106 in (268 cm) long and weighed 243 lb (110 kg). The sizes of 132–144 in (335–365 cm) found in the literature must be considered exaggerations caused by Fowler's inaccurate estimates.

distribution

Distributed widely in littoral waters on both sides of the tropical and subtropical Atlantic. Ranges from tropical West Africa to the Cape Verde islands in the east and from southern Brazil to North Carolina and Rhode Island in the west. Also found on the western coast of America from the Gulf of California to Panama and Ecuador. Abundant in the shallow waters of tropical Florida and the Caribbean.

habitat

Small juveniles are found in shallow coral reefs and grass flats. Juveniles ranging in size from 47 to 67 in (1,200–1,700 mm) are found around shallow reefs and mangrove islands. Larger juveniles and adults are found near reefs and rocky areas at depths of 66–75 ft (20–75 m) during the daytime and in much shallower areas at night.

behavior

Can be found resting on the bottom in small groups during the daytime, concealed under ledges or among boulders and rocks. These sharks often are in very close proximity to and

sometimes almost on top of one another. At dusk they disperse to search for food.

feeding ecology and diet

Said to feed chiefly on invertebrates (squids, shrimps, crabs, spiny lobsters, and sea urchins) and small fishes. A recent study of Florida nurse sharks showed that it is an opportunistic predator that consumes a wide range of species of small bony fishes, 3–9 in (8–23 cm) in length, primarily grunts. Prey typically is captured through a powerful sucking action. This suction accounts for the coral debris and solitary corals occasionally encountered in the stomach contents. Castro's study did not support the common belief that the nurse shark preys heavily on spiny lobsters and other crustaceans.

reproductive biology

The nurse shark is a viviparous species without a placenta. In Florida and the Bahamas the mating period apparently extends from the last week in May to July, but most observations of mating have been made in mid-June. The embryos are enclosed in horny egg capsules for the first weeks of gestation. Embryos hatch out of the egg cases when they reach 8.9–9.2 in (21.8–23.3 cm). The embryos are lecithotrophic, that is they are fed from yolk stored in a yolk sac, and there is no evidence of any other mode of embryonic nourishment.

The embryos are in different developmental stages through the first four months of gestation. In females examined in October, some embryos measuring 8.5–9.2 in (21.5–23.3 cm) were still inside the egg cases, while others measuring 10.6–10.9 in (27–27.8 cm) had fully absorbed yolk sacs, open yolk sac scars and appeared ready for birth. During the last month of gestation all the embryos were in the same stage of development, that is, they all had absorbed the yolk sac and apparently were ready for birth. These embryos at different stages may have been a result of ovulation of the very large oocytes (2.3–2.4 in, or 5.9–6 cm, in diameter) and encapsulation of the eggs, lasting for two or three weeks, and of the very rapid development of the embryo thereafter. Females expel the empty egg cases after the embryos have hatched out of them.

The embryos measure 11.4–12 in (29–30.5 cm) at birth, after a gestation period estimated at about five to six months. Brood sizes are large, ranging from 21 to 50 young, with a median of 32. Aquarium observations on parturition suggest that the young are released over a period of a few days, usually at night. The reproductive cycle of the nurse shark encompasses a five- to six-month gestation period and a biennial reproductive cycle. After the gestation period of five to six months and birth in late November or early December, a female does not mate again until 18 months later, in June; thus reproduction is biennial.

conservation status

Not listed by the IUCN.

significance to humans

The greatest value of the nurse shark probably lies in ecotourism. The nurse shark is the species of shark most often seen by recreational divers in Florida and the Caribbean. Because it is a large but harmless species, the nurse shark thrills divers that see one unexpectedly or at close range. In the last decade, numerous shark-watching operations have emerged in Florida and the Bahamas. In some locations nurse sharks have become habituated to being fed by divers. Although the long-term consequences and risks of these operations are still unclear, one can hope that public awareness and concern may result in some form of protection for these interesting animals. This species is one of the most common sharks in aquaria, because of its hardiness and its ability to survive in confinement for many years. According to Clark, one specimen survived 25 years at the Shedd Aquarium in Chicago, and another lived for 24 years at the Government Aquarium in Bermuda. The nurse shark is one of the most important species in shark research.

Tasseled wobbegong

Eucrossorhinus dasypogon

family

Orectolobidae

taxonomy

Eucrossorhinus dasypogon Bleeker, 1867, Indonesia.

other common names

English: Ogilby's wobbegong.

physical characteristics

Bottom-dwelling, large shark with flattened body, wide mouth, and two dorsal fins set far back in the body. Head very flat, with a frill, or beard, of fleshy protuberances, known as dermal lobes, surrounding the outline of the head. These protuberances serve to break up the outline of the head against the bottom vegetation or rocks. Color is yellowish-brown or grayish-brown, with numerous reticulations and blotches. Coloration and frill of dermal lobes surrounding the outline of the head camouflage the shark very effectively against the bottom.

distribution

Western South Pacific in the shallow waters of Indonesia, Papua New Guinea, and northern Australia.

habitat

Found in shallow coral reefs. Poorly understood but the most commonly observed wobbegong in the Great Barrier Reef.

behavior

Appears to be an ambush predator that waits for its prey while camouflaged against the bottom.

feeding ecology and diet

Details of its feeding ecology are not known.

reproductive biology

Its reproductive processes are not known. It is believed to be ovoviviparous.

conservation status

Not listed by the IUCN.

significance to humans

The species has little economic importance, other than as an attraction for fish watchers. Some attacks on divers have been attributed to this species. Its effective camouflage and large size make it potentially dangerous to divers, who may inadvertently approach it too closely, causing it to bite in self-defense.

Whale shark

Rhincodon typus

family

Rhincodontidae

taxonomy

Rhincodon typus Smith, 1828, South Africa.

other common names

None known.

physical characteristics

Largest fish in the world. The average size for this species is 18–32.8 ft (5.5–10 m). The largest specimen measured was slightly over 39.4 ft (12 m) in length. It is said to grow larger, but no one has actually measured a whale shark over 40.03 ft (12.2 m). Very short snout, with a huge terminal mouth; its nostrils have short, blunt nasal barbels. Three pronounced longitudinal ridges along each side of the trunk, the lowermost ridges becoming strong caudal keels near the tail. Covered with white or yellowish dots and irregular bars. The spots, vertical bars, and longitudinal ridges along the flanks create a checkerboard appearance.

distribution

Cosmopolitan in tropical and subtropical waters.

habitat

Pelagic species that often approaches coastal areas.

behavior

A sluggish shark, it often is seen swimming slowly on the surface, scooping up plankton and small fishes with its huge mouth.

feeding ecology and diet

Feeds on plankton. Plankton feeding is the most common and efficient feeding strategy of the largest sharks and most whales. Despite its being a ubiquitous species, we know very little about its feeding ecology.

reproductive biology

This species is viviparous. Very little is known about reproduction of the whale shark, because only one gravid female has been examined. On 15 July 1995, a pregnant female was harpooned off the east coast of Taiwan. This female, estimated at about 35 ft (10.6 m) and weighing 17.6 tons (16 metric tons), contained about 300 embryos in the uterui. As in the nurse shark, the embryos were in different stages of development. Some 237 of the embryos measured from 16.5 to 25.2 in (42–64 cm) in length; the largest embryos, at 22.8–25.2 in (58–64 cm), were probably ready to be born. This mode of reproduction is very similar to that of the nurse shark, where lecithotrophic embryos are found at different stages of development and hatch out of their egg cases at different times. This brood of 300 young is by far the largest reported for any elasmobranch.

conservation status

The whale shark has been the subject of much attention; it is protected in some countries, although there are few actual threats to this ubiquitous species. The only active fisheries at the time of this writing are in India and Taiwan. The effects of these fisheries on the Pacific Ocean population are unknown. There are no whale shark fisheries in the Atlantic Ocean. This species is listed as Vulnerable by the IUCN.

significance to humans

Seeing this gigantic, harmless creature in the water is often an unforgettable experience. One ecotourism operation has developed around Ningaloo Reef, Australia, where whale sharks can be spotted at certain times of the year. Similar operations may develop elsewhere, given the general interest in whale sharks.

Zebra shark

Stegostoma fasciatum

family

Stegostomatidae

taxonomy

Stegostoma fasciatum Smith, 1828, type locality not specified.

other common names

English: Leopard shark.

physical characteristics

Large species, reaching more than 9.8 ft (3 m) in length. Stout body with very long tail, almost as long as the rest of the body; short nasal barbels; and spectacular yellow coloration. The young are blackish-brown with vertical yellowish stripes and spots, hence the name zebra shark (although the coloration is the reverse of that of a zebra). Adults are yellowish with dark spots; hence the name leopard shark. Both juveniles and adults are easy to identify.

distribution

Found throughout the Indo-Pacific region.

habitat

Shallow coastal areas and coral reefs.

behavior

Its behavior is poorly known, except that it often is seen resting on the bottom in coral reef areas.

feeding ecology and diet

Feeds primarily on gastropods, bivalves, and small fishes. Consumes large numbers of snails. Their spiral valve intestines often are full of the opercula (the horny or shell covering on a snail's shell that closes the shell opening) of snails that they have digested, with the opercula stacking up like coins in the intestine.

reproductive biology

Oviparous (egg layer). The egg cases are large, about 5.9–3.9 in (15–10 cm), and are provided with hairlike fibers that anchor them to the bottom.

conservation status

Not listed by the IUCN.

significance to humans

Caught for food throughout its range. Small numbers are captured for the aquarium trade. The large adults are beautiful display fishes in large oceanaria. The species is of little economic importance.

Resources

Books

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Bonaterre, J. P. Tableau Encyclopédique et Méthodique des Trois Règnes de la Nature. Paris: Panckoucke, 1789.

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Dodrill, J.W. "A Hook and Line Survey of the Sharks Found Within Five Hundred Meters of Shore Along Melbourne Beach, Brevard County, Florida." Master's thesis, Florida Institute of Technology, 1977.

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Masefield, J., ed. Dampier's Voyages. 2 vols. New York: E. P. Dutton, 1906.

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Periodicals

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Carrier, J. C., H. L. Pratt, Jr., and L. K. Martin. "Group Reproductive Behaviors in Free-Living Nurse Sharks, Ginglymostoma cirratum." Copeia 1994, no. 3 (1994): 646–656.

Castro, J. I. "Biology of the Blacktip Shark, Carcharhinus limbatus, off the Southeastern United States." Bulletin of Marine Science 59, no. 3 (1996): 508–522.

——. "The Biology of the Nurse Shark, Ginglymostoma cirratum, off the Florida East Coast and the Bahama Islands." Environmental Biology of Fishes 58 (2000): 1–22.

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Coles, Russell J. "Notes on the Sharks and Rays of Cape Lookout, N.C." Proceedings of the Biological Society of Washington 28 (1915): 89–94.

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Joung, S. J., C-T Chen, E. Clark, S. Uchida, and W. Y. P. Huang. "The Whale Shark, Rhincodon typus, Is a Livebearer: 300 Embryos Found in One 'Megamamma' Supreme." Environmental Biology of Fishes 46 (1996): 219–223.

Klimley, A. P. "Observations of Courtship and Copulation in the Nurse Shark, Ginglymostoma cirratum." Copeia 1980, no. 4 (1980): 878–882.

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José I. Castro, PhD