Zebra Shark

Taxonomy:

Phylum– Chordata

Class– Chondrichthyles

Order– Orectolobiformes

Common Name– Carpet Sharks

Family– Stegostomatidae

Common Name– Zebra Sharks

Genus– Stegostoma

Species– fasciatum

Status: IUCN Red List ENDANGERED

Average Size and Length: An egg case measures 17x8x5 cm. Hatchlings measure between 20-36 cm/7.9-14.1 inches. Mature males measure between 147-183 cm/4.8-6 feet. Mature females measure between 169-183 cm/5.5-6 feet. They can possibly reach a maximum of 354 cm/11.6 feet but are mostly found at a length of less than 250 cm/ 8.2 feet.

Average Weight: They have been recorded anywhere from 44-66 pounds.

Current Rare Mythical Sightings: The Zebra shark was first described as Squalus varius by Seba in 1758. No type specimen was elected, though Seba included a comprehensive description in Latin and an accurate illustration of a juvenile. Müller and Henle placed this species in the genus Stegostoma in 1837, using the specific epithet fasciatus from an 1801 work by Bloch and Schneider. In 1984, Compagno rejected the name “varius/m” in favor of “fasciatus/m” for the Zebra shark. Both S. fasciatum and S. varium are currently in wide usage for the Zebra shark.

There is healthy morphological support for the placement of the Zebra shark, the Whale shark (Rhincodon typus), and all of the Nurse sharks in a single clade. However, the interrelationships between these taxa are disputed by various authors.

Dingerkus (1986) suggested that the Whale shark is the closest relative of the Zebra shark, and proposed a single family encompassing all five (now six) species in the clade. Compagno (1988) suggested attraction between this species and either Pseudoginglymostoma or a clade containing Rhincodon, Ginglymostoma, and Nebrius. Goto (2001) placed the Zebra shark as the sister group to a clade containing Rhincodon and Ginglymostoma.

Teeth and Jaw: Their mouths are small and transverse and are in front of lateral eyes. The mouth is nearly straight, with three lobes on the lower lip and furrows at the corners. There are 28–33 tooth rows in the upper jaw and 22–32 tooth rows in the lower jaw; each tooth has a large central cusp flanked by two smaller ones.

Head: The head is large, slightly flattened, with a short, blunt snout. The eyes are lateral, small and placed on the sides of the head; the spiracles are located behind them and are as large or larger. Each nostril has a short barbel and a groove running from it to the mouth.

Tail: Zebra sharks have a broad caudal fin or tail fin that is as long as their bodies. It has a barely developed lower lobe and a strong ventral notch near the tip of the upper lobe.

Demographic, Distribution, Habitat, Environment and Range: The Zebra shark can be found in the Indo-west Pacific in eastern Africa to Japan, New Caledonia and Palau on tropical continental and insular shelves. They have been recorded in South Africa to the Red Sea and the Persian Gulf (including Madagascar and the Maldives), to India and Southeast Asia (including Indonesia, the Philippines, and Palau), northward to Taiwan and Japan, eastward to New Caledonia and Tonga, and southward to northern Australia. They can be found on coral reefs and offshore sediments from the intertidal zone to 203 feet.

Adult Zebra sharks and large spotted juveniles will rest in coral reef lagoons, channels and faces. The striped young are rarely seen, they may be found deeper than 164 feet.

Movements of up to 87 miles have been recorded for individual sharks. However, genetic data indicates that there is little exchange between populations of Zebra sharks, even if their ranges are contiguous.

Diet: Zebra sharks feed on mollusks, small bony fish, crustaceans, and possibly sea snakes.

The Zebra shark may be preyed upon by larger fishes and marine mammals.

Ram-Suction Index: It is high on the suction side of the index. Its small mouth and thickly muscled buccal cavity allow it to create a powerful suction force extracting prey from hiding crevices.

Aesthetic Identification: Zebra sharks have cylindrical, large slender, flexible, rigid bodies with a unique banded (juvenile) or variable spotted (adult pattern). Young Zebra sharks are dark brown dorsally and yellowish ventrally. They have vertical yellow stripes and spots separating dark saddles, which break up into small brown spots on yellow in sharks that are between 50-90 cm/1.6-2.9 feet long. The spots are more uniformly distributed on larger sharks. Adults typically have 5 longitudinal ridges with a pattern of dark spots on a pale background. One ridge runs along the dorsal midline and two on the sides. The dorsal midline ridge merges into the first dorsal fin, placed about halfway along the body.

The last 3 of the 5 short gill slits are positioned over the pectoral fin bases, and the fourth and fifth slits are much closer together than the others. There are two spineless dorsal fins. The first dorsal fin is set forwards on the back and is much larger than the second dorsal fin. The pectoral fins are large and broad. The pelvic and anal fins are much smaller but larger than the second dorsal fin. The anal fin is close to the tail.

In 1964, a partially albino Zebra shark completely lacking spots was discovered in the Indian Ocean. The shark, a 6.2-foot-long mature female.

Biology and Reproduction: Zebra sharks are oviparous. They lay large, dark brown to purplish-black egg cases, which are anchored to the bottom with fine tufts of fibers. The adhesive fibers emerge first from the female’s vent; the female circles vertical structures such as reef outcroppings to entangle the fibers, so as to anchor the eggs. Females have been documented laying up to 46 eggs over a 112-day period. In captivity, the eggs hatch after four to six months, depending on temperature.

The courtship behavior of the Zebra shark consists of the male following the female and biting vigorously at her pectoral fins and tail, with periods in which he holds onto her pectoral fin and both sharks lie still on the bottom. On occasion this leads to mating, in which the male curls his body around the female and inserts one of his claspers into her cloaca. Copulation lasts for two to five minutes. (Kunize, K. & Simmons, L. (2004). “Notes on Reproduction of the Zebra Shark, Stegostoma fasciatum, in a Captive Environment“. In Smith, M.; Warmolts, D.; Thoney, D. & Hueter, R. (eds.). The Elasmobranch Husbandry Manual: Captive Care of Sharks, Rays and their Relatives. Special Publication of the Ohio Biological Survey. pp. 493–497).

Males attain sexual maturity between 4.8–5.9 feet long, and females at around 5.5 feet long. Their lifespan has been estimated to be 25–30 years in the wild.

There have been two reports of female Zebra sharks producing young asexually. An additional study has observed parthenogenesis in females regardless of sexual history. (“Zebra shark at centre of ‘virgin birth’ mystery” (January 5, 2012). BBC News. Retrieved on January 5, 2012.)

Known parasites of the Zebra shark include four species of tapeworms in the genus Pedibothrium.

Behavioral Traits, Sensing and Intelligence: The behavior of Zebra sharks is poorly known. They may rest propped up on their pectoral fins with their mouths gaping open, facing the current. This aids in oxygen respiration for the sharks and helps them breathe.

Zebra sharks are usually solitary, aggregations are rare and may happen seasonally. They are sluggish by day, and more active at night or when food is present; typically, nocturnal and resting motionless on the sea floor by day. They can swim strongly and wriggle and squirm into crevices in search for food.

Off southeast Queensland, aggregations of several hundred Zebra sharks form every summer in shallow water. These aggregations consist entirely of large adults, with females outnumbering males by almost three to one. The purpose of these aggregations is yet unclear; no definite mating behavior has been observed between the sharks. (Dudgeon, C.L.; Noad, M.J. & Lanyon, J.M. (2008). “Abundance and demography of a seasonal aggregation of zebra sharks Stegostoma fasciatum“. Marine Ecology Progress Series. 368: 269–281).

There is an observation of an adult male Zebra shark biting the pectoral fin of another adult male and pushing him against the sea floor; the second male was turned on his back and remained motionless for several minutes. This behavior resembles pre-copulatory behaviors between male and female sharks, and in both cases the biting and holding of the pectoral fin has been speculated to relate to one shark asserting dominance over the other. (Brunnschweiler, J.M. & Pratt, H.L. (Jr.) (2008). “Putative Male – Male Agonistic Behaviour in Free-Living Zebra Sharks, Stegostoma fasciatum“. The Open Fish Science Journal. 1 (1): 23–27).

Speed: They are very slow-moving; however, they can be strong and agile swimmers. They have been observed hovering in place in steady currents by waving their tails.

Zebra Shark Future and Conservation: Zebra sharks are common (much less now than in the past) but endangered due to their heavily fished range and desired meat, skin, and liver oil (except in Australia). The Zebra shark is taken by commercial fisheries across most of its range, using bottom trawls, gillnets, and longlines. They also suffer from degradation and the loss of their coral reef habitat. They are kept in captivity. Zebra shark are sought out in dive tourism and ecotourism.

Zebra Shark Recorded Attacks on Humans: They are docile, not aggressive and not a threat to humans. However, they will defend themselves if provoked or threatened. There are records of divers who have been bitten after pulling on their tails or attempting to ride them.