Overseas tourists have begun to doubt the value of a trip to the ailing Great Barrier Reef and it is getting increasingly difficult to “show people what they expect to see”, a dive operator has told a federal Senate inquiry.

A Port Douglas operator, John Edmondson, said “last-chance tourism” was spurring on other visitors but there had been a “weird” lull in bookings this year after back-to-back mass bleaching events made dead coral an unavoidable sight on reef visits.

Edmondson told the environment and communications committee in Cairns on Tuesday that while experienced reef tourists still hailed the Great Barrier Reef as the world’s best coral expanse, it was “harder to get the coral and show people what they expect to see”.

He said packages that cost the average family $800 for a day on the reef were becoming a harder sell, with “forward bookings definitely softer this year”.

This was despite a favourable exchange rate and security concerns in other countries with reef destinations, he told the committee, which is running an inquiry into the impact of climate change on the marine environment.

European reef visitors were routinely raising the issue of Australian government support for the Adani mine as a sign it was “going in the wrong direction” in its policy on climate change – the reef’s greatest threat, Edmondson said.

The Queensland Liberal National senator Ian Macdonald asked Edmondson, who studied marine biology, whether he believed “like [former US president Barack] Obama” it was the last chance to see the reef.

“It’s nearly the last chance,” Edmondson said.

While visitors to the reef were still deeply impressed, “you’re getting a creeping increase of people that had a great day – but you can see there was a lot of dead coral”, he said.

Asked by Macdonald if he deliberately took tourists to “dead coral places”, Edmondson said: “You can’t avoid dead coral.

“I think what’s happening now is some people think it’s just not worth it because of what they’ve seen and read, and that’s offset by other people that know it’s only going to get worse, and see it now.”

Edmondson’s business, Wavelength Reef Cruises, takes 22,000 people a year to see the reef, employs 20 people including marine biology graduates and takes $4.5m in revenue a year.

It was “a fantastic business at the moment” but the “very poor trajectory” of the reef was a real concern and he had held back a $3m investment in a fourth boat, Edmondson said.

“We’ve postponed our decision because with the current situation you just don’t want to be too exposed,” he said.

Macdonald questioned why tourists were linking Adani to the state of the reef, saying: “I struggle to see the connection.”

Edmondson said most travellers were “fairly wealthy, they’re mostly educated, they’re aware of what’s in the media” and those with knowledge of coral reefs understood the key threat to the reef was climate change.

They saw support for the Adani mine as counter to moves towards a lower carbon economy, he said.

“If you come from the UK or France or Holland, windmills are a more common thing, renewable energy, much more electric cars – are we deserving of their money as custodians of the reef?”

Edmondson told Macdonald that “politically I’m basically a Liberal voter who gets frustrated that, [on] the right wing of the centre right of politics, basically environmental issues are pushed over to the other side”.

The broader public did not know what to believe about the reef amid “sensationalist” media coverage of the bleaching and responses from an industry that had left “real gap in advocacy for the reef” on climate change, he said.

Tropical Tourism North Queensland had sent an email urging its dive operator members by email to provide a “tsunami” of good news stories to counter bad publicity.

“The reality is that there’s been a very dramatic change and a shifting in baseline in a lot of areas,” Edmondson said. “You can still go out and have a fantastic day and the reef is still probably the best-managed reef in the world.

“But it’s an expensive day. It’s $250 [a person] for most boats to go out to the reef and people have got a very high expectation.

“To give them their value for money and give them a good product is getting harder and harder because it’s harder to get the coral and show people what they expect to see.”