After more than 40 years trawling the waters off Newcastle in NSW, fisherman Brett Bollinger has only pulled up nets of rotten dead fish on a few occasions.

Each time coincided with seismic testing being conducted off the coast.

"The smell is the thing that gets you and it never happens any other time," Mr Bollinger said.

"It just smells like dead seafood, which is a foul, strong smell, and you think, well, the ocean on the bottom is dead and something's done it."

Now gas exploration company Asset Energy is planning another round of seismic surveys 30 kilometres offshore from Newcastle, starting on April 9.

A ship towing a single acoustic air gun will set off hundreds of sonic blasts to measure the geology of the seabed in the hope of finding a large gas deposit.

While seismic testing can often go for months, Asset Energy said its "very small" 2D seismic survey will last no more than four days, and only cover a small targeted area of 12 square kilometres.

But the company has confirmed the survey will partially overlap with a famed fishing ground known by fishermen as The Farm.

With 40 years' experience as a commercial fisherman, Brett Bollinger wants the public to listen to his first-hand experience. ( Supplied: Oceanwatch Australia )

"It's like a farm because it's a bit of ground that produces," Mr Bollinger said.

"Now they're starting to realise that there is a problem with seismic testing, it seems like a stupid idea to do it in an area that is a nursery ground for fish.

"What also worries me is not only the fish we're getting in our net, but what about the stuff that's at the bottom that those fish live off? The worms and the whole food cycle that it all starts from."

Impact on plankton significant

Most research on the environmental impact of seismic testing has focused on cetaceans, such as whales and dolphins, and suggests the sonic blasts can cause stress to the mammals and sever communication channels.

The whale watching industry, a huge tourism drawcard for the region of Port Stephens north of Newcastle, has also called for Asset Energy's testing to be stopped until more is known about the environmental impact.

"We're not raving environmentalists, we've very concerned about it," whale tourism operator and Marine Parks Association chairman Frank Future said.

Tiny shrimp-like zooplankton like this Euphausiid Calyptopsis form the base of the ocean's food chain. ( Supplied: Institute for Marine and Antarctic Studies/Anita Slotwinski )

"And the fact that they haven't consulted broadly really does disturb me."

But the impact on invertebrates, such as tiny shrimp-like plankton, is a new area of research for Australian scientists at the Institute for Marine and Antarctic Studies in Tasmania, who recently found a single sonic blast had a devastating impact.

"About two-thirds of the plankton were killed and right up to 1,200 metres, that was the real surprise," Associate Professor Jayson Semmens said.

"Previous work done in a lab had suggested you're only looking at tens of metres, maybe 10 metres.

"And so it was quite a surprise that we saw right out to 1.2 kilometres and that was as far as we tested, so it could have been more."

While plankton can regenerate, Professor Semmens said it depended on the type of plankton, the climate and ocean currents.

In the tropics it could take some species six days to regenerate, in deep cold water maybe six months.

Important part of food chain

And any mass die-off of plankton over hundreds of kilometres could have broader implications.

"People don't see plankton and don't really know what plankton are, but they're the most important thing in the food chain," Professor Semmens said.

"There's fish feeding on them, there's sea birds feeding on those fish, and seals and everything, they're the base … if you affect them then you can impact on entire food chain."

In separate studies, the researchers also found seismic surveys have a detrimental impact on scallops and developing lobster larvae.

The research is being partly funded by the fishing industry and oil and gas industry, and Professor Semmens said more was needed to gather solid information.

"No-one's saying these things [seismic testing] need to stop. We just need to work out how various industries, various users of the ocean, can work together so that we lessen the impacts," he said.

"And it might be that this time of year, a particular time of year when there's lots of larvae species in the water, try not to do them in this area, those sorts of things."

The whale-watching industry also is concerned about the seismic testing. ( Supplied: Fiona Harvey )

No impact, says exploration company

The upcoming seismic testing in Newcastle was approved by the Federal Government's National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) after what the company described as a rigorous environmental assessment process.

"We don't anticipate any damage to the marine environment through our planned survey," corporate development manager Tobias Foster said.

"We've undertaken considerable acoustic energy modelling to understand the potential implications of our release of energy into the marine environment.

"And during the survey we will be engaging qualified marine mammal observers that will have the power to affect our survey should they encounter or observe whales and other cetaceans."

But the company has faced opposition from hundreds of people who gathered to protest in Newcastle last month, as well as the Greens and the NSW Government itself.

War of words between ministers

NSW Resources Minister Don Harwin said he did not have a principle-based objection to seismic testing, but did call on federal minister Matt Canavan to reject Asset Energy's application.

"Because I want him to move to the tougher standards that we've got here in the state of NSW, compared to the less stringent approach they've got offshore in commonwealth waters," Mr Harwin said.

Matt Canavan says any application for an offshore gas facility is a long way off and would involve rigorous environmental assessment. ( ABC News )

He said tougher penalties for companies, better standards and upfront community consultation were needed at a federal level, an idea Mr Canavan said he fundamentally rejected.

"The advice I have is that the company and the regulators have ensured that the timing and the size of the seismic testing has been done to prevent environmental harm, and that's what we expect the regulator to do," Mr Canavan said.

"I'm not going to take lectures from a NSW Government that basically doesn't produce any gas in its state at all.

"So I'm not sure how you could benchmark the NSW Government's gas regulatory system when they're just not producing anything, and they're relying on the rest of the country to keep their businesses alive."

Growing issue globally

While seismic testing is a common and accepted method for oil and gas exploration, the practice is more contentious overseas, particularly in the United States where President Donald Trump plans to open up a large swathe of the Atlantic Coast for new exploration.

Professor Semmens said his research had garnered little attention in Australia, yet he had been bombarded by media requests internationally when his findings were released late last year.

And while the experience of Mr Bollinger was hard to qualify, Professor Semmens said there had been other Australian fishermen putting forward anecdotal evidence of hauling up rotten seafood after seismic testing.

Mr Bollinger said he was not surprised.

"People don't pay attention to professional fishermen because we're not scientists," he said.

"We might have 50 or 60 years experience in the industry, but they just think they can write off what we say as garbage or it's not worthwhile information.

"Mostly professional fishermen have more idea about what's on the ocean and want to protect the ocean, because if you wreck the ocean we haven't got a job."