ANY normal spider crab would run away from its approaching predator. But this crustacean had other plans when it saw a Port Jackson Shark swimming its way.

Caught on camera by the environment department's baited underwater video monitoring, this feisty crab makes two attempts at jumping on the back of a small shark before it is thrown off and the surprised hunter slinks away.

"The food source is riding its predator - that's why we say its Evel Crab-knievel," environment department marine parks program manager Chris Thomas said.

"You never would see that, it would normally run away from its predator but now its jumped on for a ride."

Mr Thomas said more footage like this was likely to be captured when the State Government implements 19 planned marine parks off the state's coast.

The marine parks will include areas called sanctuary zones where fishing will be banned.

"There's quite a lot of interest from universities and schools in doing research in sanctuary zones because they'll be control sites," Mr Thomas said.

Meanwhile, resistance among fishers to marine parks off the state's coast is falling but about a third are still concerned about commercial losses, government data reveals.

The Environment Department has been surveying attitudes to its plans to introduce 19 marine parks in state waters annually.

The results show the proportion of fishers opposed to the plans has fallen from 55 per cent in 2009 to 39 per cent this year.

But a third of regional people are still concerned about loss of commercial benefits, up from 22 per cent in 2009.

Environment department marine parks manager Chris Thomas said the figures showed the Government's message was cutting through.

"The people who are most affected ... or perceive they are, they're starting to come on board," he said. "They've seen how their feedback has been taken into account."

One example of this involved moving a no-fishing zone from near the boat ramp at Victor Harbor further around to Port Elliot to appease local fishers, he said.

The surveys also found:

OVERALL 88 per cent of people are in favour of marine parks.

THE level of support for sanctuary or no-take zones, where fishing is banned, is at 66 per cent in the city and 54 per cent in the country.

ONE in five people do not realise they can still fish in most areas of marine parks.

FEW people believe marine parks will result in cleaner beaches and water or less rubbish but almost half believe they will result in increased fish stocks.

The Government has released regional impact statements for all 19 planned parks for final public consultation.

To comment visit www.environment.sa.gov.au/marineparks/home

Originally published as 'Evel Crabknievel' surfs on a shark