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Are we seeing more sharks than usual at this time of year?

There have been lots of shark sightings around Australia in the last week. Are we seeing more sharks than we'd normally see at this time of year?

great white shark

Great white or white pointer sharks are long-distance swimmers. (Source: iStockphoto)

There have been lots of shark sightings around Australia in the last week. Are we seeing more than we'd normally see at this time of year? And how likely is it to spot white pointers as far north as Queensland?

Just last week, a female tour operator was attacked by a small shark near Perth, there were reports of shark sightings off the New South Wales coast and swimmers in Queensland were warned to keep an eye out for a six-metre shark seen lurking near North Stradbroke Island.

Shark sightings are more common during summer than winter, says Dr Charlie Huveneers from South Australia's Flinders University.

But the reason why we see them now is simply because it's that time of year when we're more likely to go swimming. And as we enter their world, encounters are more common, Huveneers says.

In fact, we know very little about the world of a creature many of us instinctively fear, even if we don't live anywhere near the ocean.

There are over 400 species of shark. Most of these species such as the grey nurse shark are harmless to humans.

Only three species, white pointers (also called great whites or white sharks), bull sharks and tiger sharks may pose a threat if they come in contact with humans, says Huveneers. But attacks are very rare — according to the latest statistics in the last 20 years, there have been 24 recorded fatalities due to shark attacks, which averages 1.2 per year.

While white pointers prefer temperate waters, they do range as far north as Rockhampton along the east coast. But just why they stray out of temperate waters is still unknown, he says.

"Whether they're following other fish or migrating whales remains a mystery."

Likewise, while tiger sharks prefer subtropical waters, they have been seen as far south as Albany on the Western Australian Great Southern Ocean coastline.

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Monitoring migration

Professor Rob Harcourt from Macquarie University agrees we are only just learning about the migration patterns of many sharks.

While shark numbers are increasing, they're not showing up in areas we haven't seen before, Harcourt says.

Harcourt is involved with an acoustic transmitter and satellite tagging program, keeping an eye on white pointers as part of the Australian Animal Tagging and Monitoring System.

"Acoustic curtains located off Australia's east coast and extending right around to Western Australia's Ningaloo reef are picking up very long-range movements of white pointer sharks," says Harcourt.

"Great whites from Tasmanian waters are turning up off Western Australia and up into Queensland, while Western Australian great whites are turning up off the coast of South Africa".

But we don't know enough about great whites to tell whether this is normal migratory behaviour or due to other factors such as ocean warming, says Harcourt.

"We're still just scratching the surface really on the extent of the movements of these animals."

Even less is known about other shark species such as bull sharks that need very specific sea temperatures.

Bull sharks follow the eddies of the East Australian current. But the current is variable throughout the year in terms of how close to shore it comes, even on a daily basis.

"So when [the current] comes close to shore you tend to get a lot more of the warm water species like bull sharks, but that's more to do with temperature fluctuations rather than any long-term trends" says Harcourt.

Unlike many other sharks, bull sharks will also swim up river into fresh water.

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Under threat

What we do know about sharks is that many species, such as the grey nurse are endangered.

Over the last five or 10 years the number of grey nurse sharks has increased thanks to improved environmental protection safeguards, says Harcourt.

"Numbers on the east coast were quite low. They were heavily harvested, and easily speared out, but have been protected since 1984 and the decline has now stopped."

Even so, recent studies on the east coast indicate a population of only about 1200 animals.

So in reality, sharks have more to fear from humans than the other way round.

Associate Professor Rob Harcourt, Director of Marine Science at Macquarie University and Dr Charlie Huveneers from Flinders University were interviewed by Stuart Gary

Tags: animals, animal-behaviour, fish

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Published 04 November 2010