Eco tourism told to plan long term.

Australia's eco-tourism operators need to think ahead more than one or two generations if they want their industry to survive far into the future.

That's the message from Peter Gash, managing director of Lady Elliot Island Eco Resort, who says his experience on the Barrier Reef island proves the point.

"Mining and farming are all great things for our country, but tourism is our sustainable industry. It won't be here just for 50 years or 100 years but potentially for 500 years and more," he told AAP on Tuesday.

Lady Elliot is world renowned for the number of huge manta rays it attracts, but when Mr Gash first took over the island, he thought there were about 40 rays swimming in surrounding waters.

He was proved wrong by a group called Project Manta, headed by Kathy Townsend from the University of Queensland.

"They've now counted and identified 440 mantas which live around Lady Elliot Island for much of the year," he said, speaking at the Global Eco Asia-Pacific Tourism Conference at Noosa on Tuesday.

"People are coming from all around the world to study them, and Kathy and her crew have recently found two mantas have come down as far as North Stradbroke Island recently and one went as far as Byron Bay which is a trip of around 550km.

"These are big critters which can measure seven metres across the wingtips, and they'll come right at you in a manta train when you're swimming, with 10 or 15 in a row as they feed on plankton, then glide just underneath you one after the other.

"People come back in tears and almost unable to speak."

Mr Gash points to huge changes in the way the island operates under his direction.

Diesel consumption by generators has been slashed by 200,000 litres to 70,000 litres a year, and the resort has built a three-phase solar hybrid power station - one of the largest privately owned systems in Australia.

The island also has a desalination plant which produces more than 20,000 litres of fresh water a day, and a program continues to revegetate "the rock" as it's affectionately known.

The island had been stripped back to bare coral in the 1800s, when several metres of guano, a mixture of bird droppings and decomposed vegetation, was mined for fertiliser.

"When I'm an old man I'll be happy to be looking at Lady Elliot looking lovely and knowing the young people I've enthused will be taking it on for another 50 and 100 years, and on it goes," he said.