Zebra Shark Amazing Facts and Features

Zebra Shark Amazing Facts and Features

The zebra shark (Stegostoma tigrinum) is a carpet shark with amazing features. Think of a shark with zebra stripes as a juvenile and entirely losing them as an adult! This is an amazing feature of the zebra shark.

The zebra shark belongs to the family Stegostomatidae and is the only member of this family. It occurs all over the tropical waters of the Indo-Pacific Oceans. Sometimes, the adult of the zebra shark is mistaken as the leopard shark (Triakis semifasciata). This is because the stripe pattern in juveniles fade away and only dark spots remain, making the adult pattern appear like that of a leopard.

Due to this shark’s preference to rest on the seafloor, encounters with humans may be rare. However, learning about the characteristics and behaviors of this species is fascinating.

Scientific Classification

Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Orectolobiformes
Family: Stegostomatidae
Genus: Stegostoma
Species: tigrinum

Scientific Name: Stegostoma tigrinum

The Origin of the Name

The common name zebra shark is derived from the appearance of the juvenile Stegostoma tigrinum species. This shark when still a juvenile has stripes across its body just like that of the zebra. However, when it attains adulthood, the stripe patterns fade away leaving only small spots.

The pattern on the body of the adult zebra shark appears like that of a leopard, hence sometimes referred to as leopard shark. But, leopard shark is the common name for Triakis semifasciata and also an alternative common name for the tiger shark (Galeocerdo cuvier).

In the past, due to the difference in body pattern, the juvenile zebra shark has been described as Squalus tigrinus, while the adult as Squalus longicaudatus making them appear as separate species.

Before the acceptance of Stegostoma fasciatum as the binomial name of this species, there were several other descriptions. The first-ever description of this species was in 1758, where Seba described it as Squalus varius. Later on, Henle and Muller placed this species in an entirely new genus Stegostoma, they used the specific name fasciatum.

This name was later widely accepted with any other valid name as a synonym. The genus name is a combination of two Greek words Stego which means “covered” and stoma which means “mouth”. While the specific name fasciatum means “banded” in reference to the stripes on the body of the juvenile.

More recently, there is wide recognition of the zebra shark scientifically as Stegostoma tigrinum. Researchers believe that this senior synonym of this species should be the correct and widely accepted.

Identifying the Zebra Shark

The zebra shark has unique traits by which it differs from other shark species. Where the appearance is a major distinguishing factor, there are other features which accurately describes a zebra shark.

Distinctive Traits of the Zebra Shark

The zebra shark generally has a bullet shape with five ridges projecting from the dorsal surface and sides. One of these ridges run along the midline of the dorsal area, while two comes by the sides. The ridge on the dorsal mid-line merges with the first dorsal fin.

This shark has five gill-slits that are small, two are in front of the origin of the pectoral fins, while the last three are behind.

The zebra shark has a slightly flat head with eyes a bit smaller than the spiracles located by the sides of the head. There are the nostrils near the blunt, rounded snout with short flaps of skin (barbels) and grooves which extend toward the small mouth.

Fins

This shark has two dorsal fins with the first twice larger than the second and situated about mid-way through the body. The rear tip of the first dorsal fin is very close to the origin of the second dorsal fin. On the flanks are the pectoral fins which are large and rounded.

The caudal or tail fin of the zebra shark has a length almost the same as the main body. The pelvic and anal fin of this shark species is smaller than other fins except for the second dorsal fin.

Coloration

The adult and juvenile zebra sharks have a distinct coloration. Juveniles less than 2.2 feet (0.70m) in length are usually darker with yellow stripes and spots running across their body. These stripes are the origin of their common name.

Once they get to the adult stage, the stripes fade away leaving only dark spots on a yellowish-brown base color. The ventral side of this shark is pale yellow.

Dentition

The upper jaw of the zebra shark contains about 28 to 33 teeth, while the lower jaw contains 22 to 32 similar teeth. There is a large cusp at the center of each tooth which has a smaller cusp and on each side.

The lower lip has three lobes and at the corners of this shark’s almost straight mouth are grooves (narrow depressions).

Growth Size and Lifespan

The female and male zebra shark grow alike in size. A maximum recorded length of this species is 8.2 feet (2.5 m). However, males would attain sexual maturity at a length between 4.9 and 5.9 feet (1.5 and 1.8 m). Meanwhile, females mature sexually at an average length of 5.6 feet (1.7 m).

Researchers believe that the zebra shark can live up to 25 to 30 years. There is yet further research to determine the exact lifespan of this shark.

Habitat and Distribution of the Zebra Shark

The zebra shark occurs in the tropical and subtropical waters close to the shore. Its preferred habitat includes coral reefs, rocky reefs, and sandy bottoms. These sharks are bottom-dwellers that spend most of their daytime resting on the seafloor.

They are found over the continental and also the insular shelves, occurring to a depth of about 207 feet (62 m) from the intertidal zone. There are records of this shark species in the marine and brackish waters. Also, there are reports however not confirmed of this shark from freshwaters.

The geographical distribution of this species ranges through the tropical waters of the Indo-Pacific region. They occupy from South Africa through the Red Sea, and the Persian Gulf. Then, toward the north this shark’s distribution extends to Japan and Taiwan, toward the south it covers northern Australia, and toward the east, it reaches Tonga and New Caledonia.

Typical Behavior of the Zebra Shark

The zebra shark is a nocturnal species that spends most of its day resting on the bottom of the sea. They are slow and lethargic. These sharks are among the few shark species that do not need to continuously swim to breathe.

Sometimes, they keep their head-side lifted, supporting it with their pectoral fins, their mouth open, and facing the water current to aid respiration. They are most likely to rest in reef channels, probably because of the extra oxygen going through the tightened reef space.

At night, these sharks become more active going in search of food. While zebra sharks are sluggish, they are also strong and active swimmers. They propel in an eel-like body and tail movement. They usually hover in a steady current with a complex waving of their tails.

Feeding Behavior

When the zebra shark hunts for food, its flexible, slender body helps it to wriggle through narrow crevices in search of prey. The mouth is small with thick muscles which enables it to suck in prey hidden in holes.

The favored prey of this shark is mollusks. They also occasionally feed on crustaceans, bony fish, and even sea snakes.

Interaction with Other Sea Organisms

Predators

The predators of the zebra shark include any larger fish and other marine mammals. These large sea creatures can prey on the zebra shark once they encounter.

Parasites

Common parasites documented from the zebra shark includes four species of tapeworm, Pedibothrium spp. Others are the Branchellion torpedinis a marine leech and Pseudolacistorhynchus nanus, a species of flatworm. These parasites attach to themselves to the zebra sharks at various points.

Social Groupings

Even while zebra sharks stay solitary most of the time, there are also records of groupings involving up to 50 individuals. As observed off southeast Queensland, groupings of many zebra sharks occur in shallow water every summer.

This grouping involves most adult individuals with more females than males. The purpose of this social behavior is not clear to researchers yet. It was thought to relate to reproduction; however, these sharks do not show any defined mating behavior to suggest that.

Sometimes during this grouping, some sharks show dominance toward another by biting the pectoral fin and pinning them to the seafloor for some minutes. The individual being dominated will remain motionless and usually turned to its back. This behavior represents a kind of courtship before copulation also found in other species between the male and female individuals. But, in zebra sharks, it also occurs between two male individuals proving to be an act of dominance.

Reproduction and Life Cycle

The zebra shark is an oviparous species; thus, the females lay eggs containing their offspring. Mating in this species may involve a violent courtship where the male bites the pectoral fins of the female making both go down to the seafloor.

For copulation to occur, the male first curls his body around that of the female while inserting a clasper into the cloaca of the female. This process may take up to 5 minutes.

The females lay large eggs measuring about 6.7 x 3.1 x 2.0 inches (Length x Width x Thickness). Egg cases range from a dark brown color to purple. They have adhesive hair-like fibers by the side which enables them to fasten to the substrate.

During egg-laying, the fiber tends to come out first from the female’s vent, while the female circles a reef outcropping or any other vertical structure securing the egg. Over a 3-month period, the female zebra shark can lay between 40 to 50 eggs. Egg-laying in this species occurs in batches of around four.

After about 4 to 6 months the eggs hatch and the young ones emerge. This duration mostly depends on temperature as observed in captivity. The young upon hatching measures 7.9 to 14.2 inches (20 to 36 cm) in length. They tend to have a longer tail when compared to the body than the adults.

Zebra sharks may also reproduce asexually as reports may have it. More so, a study observed parthenogenesis in females proving that reproduction may occur without fertilization.

Sexual Maturity and Lifespan

A male zebra shark will typically reach sexual maturity at lengths between 5.0 to 6.0 feet (1.5 to 1.8 m). On the other hand, females mature at an average length of 5.6 feet (1.7 m). The zebra shark may live up to 30 years in its lifetime.

Interaction with Humans

The several ways the zebra shark may interact with humans include:

Danger to Humans

The zebra shark generally does not pose any threat to humans. They are slow and lethargic and tolerates humans approaching them underwater without antagonizing. All these does not mean they would not bite when provoked. Of course, there are records of attacks on humans by these sharks.

Attack on Humans

So far, as documented by the International Shark Attack File (ISAF), there is only one attack humans attributed to the zebra shark. This attack did not however result in any injuries.

Importance to Humans

The Zebra shark contributes economically to humans in several ways. They are taken by various fisheries because of these values they add.

Ecotourism

Zebra sharks serve as a center of attraction for ecotourist divers in areas where they occur. At these tourist diving sites; zebra sharks have adapted to the presence of humans. Divers can even hand-feed and touch the sharks without any antagonizing reaction from them.

Aquarium Attraction

Zebra sharks adapt so well to captivity, as a result, many public aquaria around the world display them as an easy-care attraction. Captive breeding of this species proved very successful. Therefore, a good number of zebra sharks come to public aquarium display and later reintroduced to the wild.

While the beautifully patterned juveniles of zebra sharks may appear suitable for the home aquarium, note that they grow too large for it. Hence, it is not advisable for hobbyists to adopt this species for a home aquarium.

Consumption Purposes

While the flesh of the zebra shark is not widely consumed as food, some local market sells the meat fresh or dried and salted for consumption. The fin is also suitable for making shark fin soup. More so, the liver oil contains essential vitamins and the remnants serve for producing fishmeal.

Conservation

The International Union for Conservation of Nature (IUCN) recently listed the zebra shark (Stegostoma tigrinum) as “Endangered (EN)” species.

This species suffers a decline in population resulting mostly from human activities. Due to their shallow habitat, they are target to local fishing. Where there is no direct evidence to show a decline in the population of this species, market availability has reduced drastically over the years. Moreover, anecdotal reports suggest less sighting of zebra sharks in areas they were normally abundant in.

Apart from fishing which is a major cause of zebra sharks’ population decline, habitat degradation contributes heavily. Human developments can lead to the destruction of coral reefs which indirectly affects the population of this species.

Other threats to the population of zebra sharks are destructive fishing methods. Examples include the use of dynamites or poison in fishing. Most of these methods have been banned by authorities, therefore, not used extensively.

The zebra shark also occurs as bycatch in fishing nets and trawls set for other fishes. This only amounts to a small percentage of population reduction.

10 Amazing Facts of the Zebra Shark at a Glance

1. The Common Name Originates from the Appearance of the Juvenile

Juveniles of this species have yellow stripes crossing their dark brown skin coloration. This pattern looks like that found on the body of a zebra, hence the name “zebra shark”.

2. Juveniles and Adults Have Different Color Pattern

While the juvenile zebra shark has notable stripes, which gave rise to their common name, the adults, only have spots like a leopard. As a matter of fact, the stripes on the body of juveniles fade away as they attain adulthood. The adult of this species only retains numerous small spots. This is why “leopard shark” is also a common name for this species.

3. Zebra Sharks are Nocturnal Species

This shark species is most active at night. They tend to rest all through the daytime at the bottom of the sea. However, at night they emerge very actively in search of prey. They wriggle through holes and crevices to extract hidden prey.

4. They are Active and Strong Swimmers

Zebra sharks are generally sluggish sharks. This is how they are especially during the day. However, this is not the case at night as they showcase their swimming skills, actively pursuing prey. With their complex waving of the tail, they propel themselves as fast as they could.

5. Zebra Sharks Have a Strong Preference for Mollusks as Meals

Mollusks make up the most part of zebra sharks’ diet. This suggests that their favored prey are mollusks. They also feed on crustaceans, sea snakes, and small bony fish.

6. They Have Sensory Organs “Barbels” that Helps in Tracking of Prey

Hanging from the front of zebra sharks’ snouts are slender skin projections called barbels. These are sensory organs that help the zebra shark to locate hidden prey. And, with their flexible body and thickly muscled lips, they can get to the prey and suck it in.

7. Mating Involves a Violent Courtship

Male zebra sharks always try to subdue the female by biting her pectoral fins violently and pinning her to the sea bottom for copulation to occur. Most times, this process is not successful because the females will resist dominance.

8. Zebra Sharks Can Reproduce Asexually

With parthenogenesis observed in females and reports of asexual reproduction in this species, the zebra shark is likely to reproduce without fertilization.

9. There are Reports of Zebra Sharks in Freshwater Habitats

Zebra sharks are primarily marine water species. They are also occasionally found in brackish waters. Surprisingly, there are reports of this same shark species in freshwater habitat. Although, these reports are yet to be confirmed.

10. Zebra Sharks are Generally Harmless to Humans

Zebra sharks tolerate the presence of humans underwater. They are less likely to initiate an attack against humans except if provoked. More so, as an ecotourist attraction, these sharks are now comfortable in the presence of humans. Divers can approach, touch, and even hand feed them without harm.

Further Reading