Thursday, January 26, 2006

Are great white sharks migration areas changing?

Despite a number of recent shark sightings in the Shire, locals and shark experts see no cause for alarm.

Local professional shark fisherman Jeff Cooke caught a 4.5m great white shark in his gill nets at 10am on Wednesday, January 18 in Augusta.

The shark was caught in 70m deep water, 40km off the coast.

"I catch mainly small sharks-the great white was an incidental catch, they are a protected species and we have to let them go," Mr Cooke said.

He did not believe there was an increase in shark numbers in the area, saying they were just part of the ecosystem.

"I might see one or two (great whites) in a year," he said.

"Sometimes I might see none and I have been here for a fair while.

"When I caught the shark there were a few other sightings in that particular week, but there are not heaps around."

The migratory patterns of the great white suggest a redistribution, not an increase in population.
"Sharks move in and out and up and down the coast chasing food and there are more people in the water than there were 20 or 30 years ago so there are going to be more sightings," Mr Cooke said.

Margaret River Boardriders president Reg Massie said that as the Cape to Cape was the most south-western point of Western Australia, it was naturally an area great whites have to pass through.

"Recent marine biology studies have shown that sharks are constantly on the move over thousands of kilometres, naturally they might swim right past us," he said.

Mr Massie said the sightings were not really alarming and that they only had an increased significance because there were more people in the water, especially through the holiday season.
"With the shark plane located in Perth, they see more sharks because they are looking for them, the frequency of sightings would have to go up," he said.

The last fatal shark attack in Margaret River occurred in 2004 when surfer Brad Smith was killed by sharks just south of Cowaramup Bay near Lefthanders Beach.

The sharks were suspected to be a 5m great white and a 3m bronze whaler.

On Wednesday, January 11, local surfer Malcolm Mortimer was at Boranup Beach when a great white surfaced and circled him before the surfer caught a wave back into shore.

The shark came in from the north and headed south.

There was also an unconfirmed sighting of a great white at Jay's Beach near the Blackwood River entrance.
"With the events that happened with Brad Smith, people are a little more aware of what's in the water with them," Mr Massie said.

"Sharks are part of the natural beauty and uniqueness of the area.

"All the Club would advise is that people are a little more diligent while in the water and report any sightings to the WA Fisheries Department and don't panic."

WA Department of Fisheries Shark Research scientist Rory McAuley said there was evidence to suggest that the great white population had been depleted over the years.

"There is a perception that the number of great white sharks is increasing as a result of receiving protected species status," Mr McAuley said.

"While I wouldn't say this is not the case, biologically speaking they can take up to 20 years to reach reproductive age and they give birth to young infrequently maybe up to every two to three years.

"Consequently it would take a couple of generations up to 40 or 50 years to see an increase in overall population size."

It is likely that that the great whites' cyclical movements are keyed into prey abundance, similar to whales and the movements of fish.

"What I understand from some of the tagging results recorded over the years is that the great white is an extremely mobile species," Mr McAuley said.

"The sightings at the moment certainly don't suggest an increase in population."


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