As wild storms swept across southern Tasmania in May, a fish pen designed to withstand the "toughest Australian conditions" broke apart, releasing thousands of Atlantic salmon into the wild.

An industrial fish feeder inside the "fortress" pen had smashed open the enclosure, and eventually washed up on a suburban beach.

Huon Aquaculture has up until now refused to confirm the true number of fish lost; however, the ABC can reveal it is around 120,000.

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The company confirmed the figure when approached by the ABC, releasing a statement:

"The number being reported by the ABC is in line with what Huon reported to the Government."

However, the reluctance to disclose the volume of escaped stock has raised further concerns about trust in an industry with massive expansion plans for waterways around Hobart, with questions arising about why Huon would not publicly reveal the scale of their losses.

"The secrecy in regard to the figure just reflects the secrecy and a lack of clarity throughout the industry and throughout all the areas where the industry is impacting natural resources that are used by recreational anglers," said Plinio Taurian, one of Tasmania's best known recreational anglers.

A Huon Aquaculture fish feeder washed up at Kingston Beach in May. ( ABC News: Ellen Coulter )

Fugitive salmon learn to hunt

Back in May, as fishermen scrambled to catch the escapees, questions were also being asked about what impact the non-native salmon could be having on local fish species and the environment more generally.

Mr Taurian and a network of fishermen studied the guts of the escaped salmon they were catching. He said in about 10 per cent of the fugitive fish there was clear evidence they were feeding on native species, despite the salmon having lived on a diet of pelletised food, without the need to hunt, up until their escape.

"When we opened up the fish we found a real mixture of food in their guts. We found small mullet, medium sized baitfish, a baby flounder, crabs and other crustaceans," Mr Taurian said.

Scientists are trying to understand if major fish escapes like Huon's in May are damaging to the broader environment.

"There's certainly a potential issue in terms of the scale of the escape event," said Jeremy Lyle, senior researcher at Tasmania's Institute for Marine and Antarctic Studies (IMAS).

"Whether it's detectable in terms of broader impacts, that's questionable."

After the May escape, Dr Lyle and his colleagues started a project inviting anglers to report the gut contents of the caught salmon.

A Huon Aquaculture enclosure washed up at Taroona during the storms. ( ABC News: Ellen Coulter )

Call for more transparency: EPA

In Huon's annual report to the Australian Stock Exchange tabled back in August, they documented a fall in "biological assets" of 10 per cent.

The figure was attributed to "poor growth, harvesting forward to meet demand, and an increased incidence of gill disease due to the extended warm summer", but did not mention the escape of 120,000 fish.

Wes Ford says there needs to be more transparency from the indsutry. ( ABC News: Fiona Blackwood )

The company said it reported the fish escapes to the Government as required.

"It is important to note that fish escapes are rare, but it was an exceptional weather event during which waves of over 11 metres passed through our Storm Bay lease," the company said in a statement.

The head of Tasmania's Environment Protection Authority (EPA) Wes Ford said there was a widely held view the salmon farming industry needed to be more open about its operations.

"I believe there should be greater transparency, I think, as does the industry, and as does the Government," Mr Ford said, adding the Government had flagged greater transparency through its 2017 sustainable growth plan for the Tasmanian salmon farming industry.

The three major players, Huon, Tassal and Petuna, have plans to effectively double production in the coming decade, with much of it in Storm Bay.

Reluctance to disclose fish deaths or escape numbers could shake community confidence in the industry, if that has not happened already — a view shared by shareholder activist and longtime industry observer Stephen Mayne.

He described the 120,000 mortality figure as a "very big number" and said "transparency is always the best option for public companies".

"I can't see why the company hasn't provided an estimate if the loss was that large it should have been disclosed."

Mr Mayne was critical of the Tasmania Government and its acceptance of a culture of non-disclosure around issues like the mass mortality event in Macquarie Harbour over summer, in which over a million fish perished, as well as the May escape.

"The Government shouldn't be tolerating such secrecy as the regulator of this industry, but you often see this with controversial industries," he said.