Theory on switching menu

Shark attacks would be far more frequent if they were preying on humans, an expert says.
Retired South Australian marine biologist Dr Scoresby Shepherd suggested sharks might be switching their prey to humans because of a decline in natural food sources, such as tuna.
He said where attacks used to happen once every 30 to 40 years, they are now happening at least once a year.

"My speculation is that if the natural prey are decreasing then they are more likely to be hungrier than before," Dr Shepherd told ABC Radio.

Dr Shepherd said it was a well-known biological phenomenon known as prey switching.
But Fox Shark Foundation's spokesman, Andrew Fox, said there was no good evidence to support Dr Shepherd's theory.

He said the rate of shark attacks had been steady at about 1.3 per year for the past 20 years.
"If you look statistically, it may well be that there is not really an increase in shark attacks relative to the amount of people that are going into the water," Mr Fox said.

"Even if there was one shark that had switched its preference, we would be seeing attacks on a very frequent basis, not just the odd investigative attack and the odd fatality every year.
"Even if it was two or three or five or 10 (fatalities a year) ... statistically, it does not indicate a prey switching."

In September, surfer Josh Berries, 26, shoved his board in a great white shark's mouth to escape an attack of South Australia's Kangaroo Island.

That came less than a week after one in Perth, when surfer Brad Satchell fought off a shark by punching it in the head at Scarborough Beach. Mr Satchell was not injured.

On September 4, surfer Jake Heron survived being mauled by a shark off South Australia's Eyre Peninsula.

The 40-year-old had been surfing about 30km south of Port Lincoln when he was attacked, but managed to fight off a four-metre great white by repeatedly punching it in the head.

That attack came less than two weeks after marine biologist Jarrod Stehbens was killed by a shark while diving for cuttlefish eggs off Adelaide's Glenelg Beach.