Sharks

Compiled by Barry Tobin

Sharks

The three sharks most dangerous to people in the tropical and temperate regions of Australia are:

Bull Shark Carcharhinus leucas

Tiger Shark Galeocerdo cuvier

Great WhiteShark
Carcharodon carcharias

Australia has more than 160 species of shark which make up nearly half of the worlds species. The vast majority of these pose no threat to humans. Those that do are more than likely cases of people being in the wrong place at the wrong time. So with care most threats are avoidable

The Great Hammerhead Shark(Sphyrna mokarran) and the much smaller( Sphyrna lewini) are not considered to be a real danger.

Description

The three shark species listed above are at the top of the marine food chain. This means they are rarely hunted themselves. Surprisingly, even though they are known man-eaters, humans are more of a threat to them than they are to humans.

The Great White Shark is the only warm-blooded species of shark, this means they can keep the temperature of their body higher than the surrounding water. All other sharks are cold-blooded. Sharks skeletal structures are comprised of cartilage instead of bone. They don't have scales like other fish, instead they have a very rough outer layer like sandpaper made of dermal denticles.

The Bull Shark also inhabits fresh water and is considered to be a very dangerous shark because of its aggressive nature and liking for shallow habitats. It has been found thousands of kilometres from the sea in the upper reaches of the Amazon River. Canal estates, such as around the Gold Coast in Australia, are a favoured location where occasional attacks have occurred.

Habitat

Shark habitats range from open ocean waters to coastal waters, rivers and coral reefs.

Shark migration is not well understood because of a lack of research in this area but it is known that food availability and reproductive cycles probably play an important part in their migration.

Behaviour

Research that has been conducted suggests that sharks undergo daily activity rhythms culminating in greater activity between sunset and well into the night.

Generally sharks will only attack humans if provoked or they're mistaken for food.

Diet

All sharks are meat-eaters with the larger sharks generally feeding on marine mammals, fish, squid, and other sharks. Bottom feeding sharks such as wobbegong, feed upon shellfish. The Whale Shark and Basking shark are filter feeders and eat tiny invertebrates such as plankton.

Sharks usually eat between 1% and 10% of their body weight weekly.

Baited video fleet yields diverse results in deep-water fish surveys

Shark attack fatalities- a few facts
What you can do to reduce your chances of being attacked

Australian Museum - Canberra, Australia
Elasmobranch research at Monterey Bay
Queensland government FishWEB - Swim with caution in warmer weather
Shark resources and information

References

Dangerous Marine Animals of the Indo-Pacific Region, (Diving Centre Monograph on identification first aid and medical treatment) 2nd reprint, Wedneil Publications (Newport, 1978), Dr. Carl Edmonds.
Cruising the Coral Coast, Alan Lucas
Guide to Beach and Water Safety, Kenneth Bullock
Encyclopaedia Britannica
Grant's Guide to Fishes, Ern Grant
Sharks and Rays of Australia, PR Last and JD Stevens