Discovered species of sharks
Sharks swimming in B.C. waters
Shark species that never attack humans
Distance a shark can hear prey
Sharks live in every ocean of the world, from the Arctic to the Antarctic. They are also seen in some rivers and lakes. Worldwide, there are over 500 species of sharks and at least 12 of them are regularly found in the waters of British Columbia.
Sharks have no bones. Instead, their skeletons are made of cartilage. Sharks also renew their teeth throughout their lives; as one tooth breaks off or wears out, another one rotates forward from the inside of the jaw to replace it. Sharks have a special valve inside their intestines that looks like a spiral staircase on its side. These spiral valves help sharks digest food by slowing its passage through their short, compact intestines. Large, oily livers also give sharks some buoyancy.
Shark skin looks and feels like it is covered with tiny teeth. In fact, their small, rough placoid scales (also called denticles), have the same structure as sharks’ teeth! Shark skin is sometimes used as sandpaper. Depending on the species, sharks have five to seven pairs of gill slits on the sides of their heads (bony fishes have one pair). Water flows out of the gill slits after passing over their gills. Contrary to popular belief, most sharks can breathe without swimming; they open and close their mouth to pump water over their gills. Sharks have asymmetrical tails: the upper half is longer than the lower half.
Sharks are internal fertilizers. That means their eggs are fertilized in the female's body. When sharks mate, the male inserts one of his claspers (a finger-like appendage on the male's underside) into the female's cloaca (genital opening). Sperm travels along a groove on the clasper into the female's body. Some sharks lay egg-filled cases on the bottom of the ocean, called devil’s wheelbarrows or mermaid’s purses. Most sharks give birth to live young; they keep their eggs within their bodies while the young sharks develop. Length of pregnancy (gestation period) in sharks varies with each species. It ranges from nine months to as long as 22 months in spiny dogfish. Depending on the species, sharks can produce between 1-135 young at one time.
All sharks are carnivores, but each species of shark hunts for different animals depending on its lifestyle:Benthic (bottom-dwelling) sharks forage for animals that live on the ocean floor including sea urchins, clams and crabs. Pelagic (open-water) sharks cruise through the ocean, hunting squids, fishes, other sharks, sea birds, and marine mammals. The largest pelagic sharks are filter-feeders. These sharks strain small fishes, krill, larvae and other types of plankton out of the water. They eat huge quantities of tiny animals.
Sometimes; all sharks are predators after all. Most shark species (about 80 percent) have never been known to attack humans. There are four shark species that have always been considered dangerous to humans: great white shark, tiger shark, bull shark and oceanic whitetip shark. 17 other species of sharks have also attacked humans. They are considered less dangerous, but can be aggressive if threatened or disturbed. They include lemon sharks, blacktip reef sharks (which can be seen at the Aquarium), nurse sharks, wobbegongs, sand tiger sharks and spitting sharks. Although they are slow and sluggish, basking sharks and whale sharks are considered dangerous because of their large size. Many shark attacks on humans are caused by people getting too close to sharks, or because they are provoked or threatened.
The most important sense sharks use to find its prey is sound. They can hear a struggling fish two km away, but they do not have external ears. Instead, a tiny duct carries sound waves to their inner ear.Sharks can also detect sound and vibrations with their lateral line system. The lateral line system consists of a series of fluid-filled canals just below the skin of the head and along the sides of the body.Sharks have an incredible sense of smell; some shark species can smell one drop of blood diluted in one million drops of sea water.
Sharks have good eyesight, especially when prey is closer than 15 metres. They have a sophisticated and complex retina but it is not well understood at present. Sharks can sense the electrical impulses produced by muscles that move in the animals they are hunting. This helps them detect animals hidden beneath the sand. Sharks with whisker-like feelers (barbells) use them to taste and feel their way to food.
Scientists have demonstrated that sharks are able to learn at a rate similar to white rats and pigeons. Sharks have inhabited the oceans for millions of years; some ancient species existed before the dinosaurs. Skates, rays and ratfishes are close relatives of sharks.
1. Ebert, David A., Fowler, Sarah and Leonardo Compagno. 2013.
2. Sharks of the World: a Fully Illustrated Guide. Plymouth, UK: Wild Nature Press.
3. Ferrari, Andrea and Antonella Ferrari. 2002. Sharks: a Firefly guide. Toronto: Firefly Books.
4. Ferguson, Ava and Gregor Cailliet. 1990. Sharks and Rays of the Pacific Coast. Monterey Bay, CA: Monterey Bay Aquarium.
Gruber, Samuel H. Ed.1991. Discovering Sharks. Highlands, NJ: American Littoral Society.
5. International Research. NOAA Fisheries.