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In-depth

JUST THE FACTS

Shark Attacks

FEATURES
Anatomy

Arctic diving

Skalugsuak’ origins

Sharks: Then & Now

Essay: Mystery of the monster

Swimming with sharks
DEPARTMENTS
• Knowledge Toolbox
• Cartographer’s table
• Just the facts
Are sharks dangerous? Not really. You’re more likely to be hit by lightning than be attacked by a shark.

There are more than 350 species of shark swimming worldwide, but most don’t bother with humans. Dangerous species found off Canadian coasts include the great white, mako and oceanic whitetip. But shark attacks are extremely rare in Canada and nobody has ever died from one. Most shark attacks happen to surfers in Australia and South Africa. Furthermore, shark attacks are on the decline.

Worldwide shark attacks in 2000: 79
Worldwide shark attacks in 2001: 68
Worldwide shark attacks in 2002: 63
Worldwide shark attacks in 2003: 55
Shark attacks deaths in 2003: 4

There are two possible reasons for the decrease: fewer sharks or fewer people swimming in shark habitats.

MEDAL WINNERS
Biggest shark: whale sharks grow to 12 metres.

Biggest Canadian shark: basking sharks reach lengths of nine metres.

Smallest shark: dwarf sharks grow to 25 centimetres.

Fastest swimmer: mako and blue shark swim from 35 km/h to as fast as 100 km/hour! These sharks can even leap out of the water.

Deepest diver: Portuguese sharks plunge to 2,750-metre depths.

Longest migration: blue sharks can wander 2,000 to 3,000 kilometres during their yearly migration from New York to Brazil.

Most abundant shark: spiny dogfish shark (which grow to 1.2-1.5 metres).

Most domestic shark: often smaller than 60 centimetres, cookie-cutter sharks can bite perfectly round chunks of flesh out of whales and dolphins.

Shark with the most wanderlust: bull sharks can swim in both fresh and salt water, and some venture from the Atlantic Ocean up in to the Mississippi River.



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SENSES
Percentage of brain devoted to smell: 2/3.
Distance that a shark can still smell a drop of blood: 0.4 kilometres.

Eyesight: sharks have excellent eyesight and can see in colour.
When some sharks attack their prey, a "nictitating" membrane descends over the eye for protection.

Unusual senses: Shark can sense low frequency vibrations in the water (like injured prey thrashing about) and can also detect the electrical impulses from the muscles and heart of their prey.

SHARK MENUS
Sharks are at the top of the food chain. Called apex predators, sharks help keep other fish and some marine mammal populations in balance.
Most sharks eat fish and invertebrates like crabs, but some also prey on seals, sea lions and even other albeit smaller sharks.

Sharks aren’t choosy.The remains of cows, dogs, penguins, reindeer and birds have also been found in shark stomachs. Researchers have found balloons, tin cans, a wristwatch, oil filters, a partial suit of armour, parts of a rocking chair and a handbag in the bellies of adventurous sharks.

LIFE AND REPRODUCTION
Sharks normally live for about 25 to 30 years, although some, like the spiny dogfish, can reach 100 years.

Sharks give birth three ways: Some lay eggs, make eggs but store them inside until they hatch, or give birth to live young.

Sharks don’t care for their young after birth, but find safe places like coral reefs to give birth or lay eggs.

Number of shark young produced at a time: 1 to 100

Gestation period (spiny dogfish): up to 2 years
Sharks have extremely long gestation periods, which make it difficult for diminished shark populations to replenish quickly.

How to determine the age of a shark: In a similar way to trees, sharks can be aged by counting growth rings on their vertebra.

SHARK POPULATION
Researchers don’t know the exact populations of all sharks, but they do know the numbers are falling. Thousands of sharks are killed by humans through shark fining (cutting the fins off a shark for shark-fin soup, then throwing the shark back in the ocean) and by-catch in the fishery industry.

Percentage decline in the past 15 years of hammerhead, white, and thresher sharks: 75 percent
Percentage decline in the past 15 years of tiger, coastal, blue, porbeagle, and oceanic sharks: 50 percent

Number of shark species in Canadian waters: more than 20
Main Atlantic species: blue, porbeagle, mako
Main Pacific species: spiny dogfish, sixgill, Pacific sleeper
Main Arctic species: Greenland, Pacific sleeper

SHARKS AND MEDICINE
Shark liver oil was used to make Vitamin A supplements.
Since shark and human corneas are similar, shark corneas have been used in eye surgery.

Shark cartilage is used to make artificial skin for burn victims and as a complementary therapy by some cancer patients.

Scientists are investigating why sharks appear so resistant to cancer. They want to develop cancer treatments for humans that copy shark cancer resiliency.

Sarah Everts

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