CHIMAERAS, SHARKS, SKATES AND RAYS: Chondrichthyes

SPOTTED RATFISH (Hydrolagus colliei): SPECIES ACCOUNTS
TIGER SHARK (Galeocerdo cuvier): SPECIES ACCOUNTS
WHITE SHARK (Carcharodon carcharias): SPECIES ACCOUNTS
ATLANTIC MANTA (Manta birostris): SPECIES ACCOUNTS
CLEARNOSE SKATE (Raja eglanteria): SPECIES ACCOUNTS

PHYSICAL CHARACTERISTICS

Chimaeras (kye-MIHR-uhs), sharks, and skates and rays are the class of fishes whose skeleton is made of cartilage (KAR-teh-lej), a tough but flexible supporting tissue. Chimaeras have large heads and long bodies that taper to a whiplike tail. The skin is smooth and rubbery and has no scales. Sharks and skates and rays have gills that open to the outside, have no swim bladder, and have a sandpaper-like skin covering rather than scales. Sharks range in size from tiny to huge. Skates and rays are flat from top to bottom and have massive pectoral (PECK-ter-uhl) fins and long, sometimes whiplike tails.

GEOGRAPHIC RANGE

Chimaeras, sharks, and skates and rays live all over the world except in the Antarctic region.

HABITAT

Chimaeras usually live on muddy bottoms near the shore. Sharks live in coastal waters on the bottom or out at sea in open water or at the bottom. Skates and rays live on the bottom in saltwater or freshwater or move back and forth between the two.

DIET

Chimaeras eat bottom-dwelling animals such as crabs, clams, and fishes. Some sharks are fierce predators (PREH-duh-terz) that hunt and eat every sort of sea animal. Others simply strain plankton, the microscopic (MY-kro-SKA-pihk), invisible to the eye, plants and animals that drift in bodies of water. Most skates and rays eat bottom-dwelling shelled animals and bony fishes.

BEHAVIOR AND REPRODUCTION

All chimaeras, sharks, and skates and rays reproduce by internal fertilization (FUR-teh-lih-zay-shun), meaning egg and sperm unite inside the female. Some species lay fertilized (FUR-teh-lyezd) eggs, and the young develop outside the mother. In other species the young develop inside the mother, hatch within the mother, and are born freely swimming. Chimaeras, sharks, and skates and rays engage in parental care before laying eggs or giving birth to pups.

CHIMAERAS, SHARKS, SKATES, RAYS, AND PEOPLE

A few species of chimaeras are fished commercially for food. Sharks are used for their meat, oil, and hides, which are used for leather. Skates and rays are eaten in some areas, and the skin sometimes is used for leather.

Big Fish, Tiny Diet

The whale shark is the largest fish in the world at a length of 59 feet (18 meters) and eats the smallest food, plankton.

Man-eater?

More people have been killed by domestic livestock, such as pigs, than by sharks.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists eight species of sharks and skates and rays as Critically Endangered, seventeen as Endangered, thirty-two as Vulnerable, sixty-four as Lower Risk/Near Threatened, and one as Lower Risk/Conservation Dependent. Critically Endangered means facing an extremely high risk of extinction in the wild in the near future. Endangered means facing a very high risk of extinction in the wild in the near future. Vulnerable means facing a high risk of extinction in the wild. Near Threatened means at risk of becoming threatened with extinction in the future. Conservation Dependent means that if the conservation program were to end, the animal would be placed in one of the threatened categories.

SPOTTED RATFISH (Hydrolagus colliei): SPECIES ACCOUNTS

Physical characteristics: Spotted ratfish have a bluntly pointed snout. The body is reddish to dark brown with silvery-blue and gold highlights. There are many small white spots on the head and along the sides and back. They are called ratfish because their teeth look like rodent incisors (ihn-SY-zrz), the sharp front teeth of a rat.

Geographic range: Spotted ratfish live in the Pacific Ocean from southeastern Alaska to northern Mexico.

Habitat: Spotted ratfish live near muddy, sandy, or rocky bottoms.

Diet: Spotted ratfish eat bottom-dwelling invertebrates (in-VER-teh-brehts), which are animals with no backbones such as earthworms or insects, and other fishes.

Behavior and reproduction: Spotted ratfish migrate or move from deeper to shallower waters. They tend to gather in groups based on age and sex. The eggs are fertilized (FUR-teh-lyezd) inside the female by sperm from the male. Two egg capsules are laid every seven to ten days for months.

Conservation status: Spotted ratfish are not threatened nor endangered.

Spotted ratfish and people: At one time spotted ratfish were fished for their liver oil. ∎

TIGER SHARK (Galeocerdo cuvier): SPECIES ACCOUNTS

Physical characteristics: Tiger sharks have a short, rounded snout and large first dorsal fins and tail fins. Young tiger sharks have dark vertical stripes over a gray background. Large females reach a length of 20 feet (6 meters). The teeth curve backward.

Geographic range: Tiger sharks live all over the world.

Habitat: Tiger sharks live mainly near the shore in muddy waters, where rivers meet the sea, near piers, in coral reefs, and in shallow lagoons. Tiger sharks may be found in open water offshore but are not truly oceanic sharks.

Diet: Tiger sharks eat whatever is available and are efficient predators. They have been known to ingest (ihn-JEHST) or swallow inedible objects, such as an amazing variety of trash. Prey varies from large fishes, reptiles, mammals, and birds to squid and shrimp.

Behavior and reproduction: Tiger sharks are mostly nocturnal (nahk-TER-nuhl), or active at night, and strong-swimming. They usually swim alone. These sharks appear sluggish because they cruise at slow speeds near the surface. Young tiger sharks develop inside the female. The female gives birth to ten to eighty-two young that are 20 to 30 inches (51 to 76 centimeters) long.

Conservation status: Tiger sharks are not threatened nor endangered.

Tiger sharks and people: In many places tiger sharks are considered dangerous. Tiger sharks are fished for their meat, hide, and liver and for sport. They do not survive in aquariums. ∎

WHITE SHARK (Carcharodon carcharias): SPECIES ACCOUNTS

Physical characteristics: The average length of white sharks is 18 feet (5.5 meters). White sharks are white on the belly and gray-to-bluish on the back and sides. The first dorsal fin is much larger than the second, and the tail fin is large and crescent shaped. The pectoral fins have black tips. White sharks have a cone-shaped snout, large black eyes, and large triangular teeth with sawlike edges.

Geographic range: White sharks live worldwide but are most common off the coasts of California, Australia, and South Africa.

Habitat: White sharks cruise through relatively shallow waters near the surface or close to the bottom. They can travel long distances in open water.

Diet: White sharks feed on bony fishes, other sharks, sea turtles, seals, whale carcasses, and even sea birds resting on the surface.

Behavior and reproduction: White sharks are solitary (SA-le-TER-ee) and nomadic (no-MAE-dihk). They move from place to place alone without settling on a fixed home. They are capable of great bursts of speed and can leap completely out of the water. The young develop inside the female. The young measure 4 to 5 feet (1.2 to 1.5 meters) at birth and can weigh as much as 55 pounds (25 kilograms).

White sharks and people: People pay a great deal of money to watch white sharks from the protection of a submerged cage.

Conservation status: The IUCN lists white sharks as Vulnerable, which means they are facing a high risk of extinction in the wild. ∎

ATLANTIC MANTA (Manta birostris): SPECIES ACCOUNTS

Physical characteristics: The head, pectoral fin, and trunk of Atlantic mantas are flattened and join to form a disk that is much broader than it is long and has slightly curved outer corners. Adults have an average disk width of 22 feet (6.7 meters). Atlantic mantas have a short, whiplike tail. Atlantic mantas are brown to olive-green on the back and white to whitish on the belly.

Geographic range: Atlantic mantas live all over the world.

Habitat: Atlantic mantas live in open coastal waters.

Diet: Atlantic mantas eat animal plankton and freely swimming crustaceans (krus-TAY-shuns), such as shrimp.

Behavior and reproduction: Atlantic mantas perform somersaults while feeding. They sometimes leap partially or completely out of the water. They enter shallow reef areas to be cleaned of parasites by small bony fishes. After internal fertilization of the eggs, the young develop inside the female. The litter size is unknown. Atlanta mantas are 4 feet (1.2 meters) wide at birth.

Conservation status: Atlantic mantas are not threatened nor endangered.

Atlantic mantas and people: Atlantic mantas are eaten in some parts of the world. Scuba expeditions are conducted to observe manta rays at their feeding sites. ∎

CLEARNOSE SKATE (Raja eglanteria): SPECIES ACCOUNTS

Physical characteristics: Clearnose skates reach a total length of 31 inches (79 centimeters). The head, pectoral fins, and trunk are flattened and join to form a broad disk. The tail makes up about one-half of the total length of the skate. The sides of the snout are not clear but are cloudy, like frosted glass. A row of thorns runs down the back. Clearnose skates are brown to gray on the back and whitish to yellowish on the belly. There are dark and light spots and dark bars on the back.

Geographic range: Clearnose skates live in the western part of the North Atlantic Ocean from Massachusetts to the northern Gulf of Mexico.

Habitat: Clearnose skates live on soft bottoms near the shore.

Diet: Clearnose skates eat worms, shrimps, crabs, and bony fishes.

Behavior and reproduction: In the northern part of their range, clearnose skates migrate (MY-grayt) north and near shore in the spring and south and offshore in the fall. After internal fertilization, the female lays eggs, and the young hatch from egg capsules after several months. At birth clearnose skates are about 5 inches (12.5 to 14.4 centimeters) long.

Conservation status: Clearnose skates are not threatened nor endangered.

Clearnose skates and people: Clearnose skates have been used in cancer research. ∎

FOR MORE INFORMATION

Books:

Allen, Thomas B. The Shark Almanac. New York: Lyons, 1999.

Perrine, D. Sharks and Rays of the World. Stillwater, MN: Voyager Press, 1999.

Pope, Joyce. 1001 Facts about Sharks. New York: DK, 2002.

Web sites:

"Ask a Scientist Answers to Chondrichthyes Questions." OceanLink. http://oceanlink.island.net/ask/chondrichthyes.html#anchor120253 (accessed on September 20, 2004).

"Chondrichthyes." Science Fair Projects Encyclopedia. http://www.all-science-fair-projects.com/science_fair_projects_encyclopedia/Chondrichthyes (accessed on September 20, 2004).