Environmentalists have raised concerns after new data showed about 10 per cent of salmon farmed in Tasmania's Macquarie Harbour died during the process.
About 9,500 tonnes of salmon was expected to be produced in the harbour on the state's west coast this year, according to Salmon Tasmania's website.
Environmental group Neighbours of Fish Farming [NOFF] submitted a Right to Information request to find out the mortality rate.
In response, the Department of Natural Resources and Environment has released data showing 1,149 tonnes of salmon died between September last year and March this year.
The month of January recorded the highest proportion of mortalities, with 313 tonnes of dead salmon.
"This is an industry that claims that it's world's best practice, that animal welfare is highest priority, and that it's an industry that's fit for purpose," NOFF president Peter George said.
"Well, clearly, it's not.
"How can they lose a million kilos of fish, 10 per cent of their product, in just one area of Tasmania?"
A Neighbours of Fish Farming spokesperson says better transparency from the salmon industry is needed. (Supplied: Bob Brown Foundation)
The released information was limited to weight statistics, and did not include the number of fish that had perished, nor the reasons for their deaths.
Mr George said greater transparency was needed.
"This is happening in public waters," he said.
"We want to know the numbers of fish that are dying, the percentage of fish that are dying, the weight and most importantly, the causes."
Mortality reporting to include fish numbers
The three aquaculture companies that operate in Macquarie Harbour — Huon, Petuna and Tassal — are required to report any elevated mortality events to the state's chief veterinary officer and the Environment Protection Authority (EPA).
Such events are when disease or mortality affects more than 0.25 per cent of fish in any individual cage a day for three consecutive days.
Last summer, 66 elevated mortality events were reported across the state, according to evidence provided to a budget estimates hearing last month.
The state-wide data for mortality events did not include a breakdown of the weight or number of salmon that had died.
However, EPA boss Wes Ford told the hearing that such information would soon be available.
"We are in the process of implementing the new environmental licence conditions that do require the companies to notify numbers or weight, depending on the circumstance," Mr Ford said last month.
Salmon Tasmania chief executive Luke Martin said the industry was the most regulated in the world and did all it could to reduce mortalities.
"The industry's aspiration is minimal amount of mortalities as possible for obvious reasons," Mr Martin said.
"No farmer wants to lose their livestock at any great rate numbers.
"But the reality is, it's just a fact of life for all farmers, and the salmon farmers are no different."
He said there was no standard mortality rate, and that a range of issues could contribute to deaths, including warmer waters, jellyfish strikes and pesticides.
"There's a variety of reasons why these mortalities happen in different farms across the state at any one year to the next," Mr Martin said.
"And the rate does jump around significantly from one year to the next, and also from one part of the state to the next."
A Tasmanian government spokesperson said the industry was subject to a "comprehensive biosecurity program" that involved routine reporting requirements and the disclosure of mortality notifications.
Pressure mounts on Plibersek to take action
A group of 34 scientists have written to federal Environment Minister Tanya Plibersek urging her to revoke environmental approvals for the salmon farms in Macquarie Harbour, and "reposition" the local community as part of a transition away from its reliance on the industry.
Ms Plibersek is currently considering whether to review the approval from 2012 to expand the farms.
Macquarie Harbour is the last known habitat of the endangered Maugean skate.
The skate relies on dissolved oxygen, and conservation advice to Ms Plibersek last year identified the salmon industry as "the most important anthropogenic contributor" to the oxygen level in the harbour.
The salmon farming industry, state MPs and local councillors have increasingly questioned scientific research on the impact of the salmon farms on the Maugean skate, and the extent of species decline.
Former director of the University of Tasmania's (UTAS) Centre for Marine Socioecology, retired professor Stewart Frusher, was among the signatories to the letter.
Stewart Frusher said it was unlikely the Maugean skate would be found in Bathurst Harbour. (Supplied)
He said he was concerned that science was increasingly being "misrepresented" in attempts to pressure Ms Plibersek.
"The ministers told them she'll take it on the science and, so they now come back and say, 'Oh, quickly, we've got to do something and question the science,'" Mr Frusher said.
The industry is helping to fund an oxygenation trial in the harbour, which the state government says has shown initial "promising results".
The letter was also signed by five fellows from the Australian Academy of Science, and included marine biologists and aquaculture researchers.
This week, Mr Martin questioned why scientists were not researching Bathurst Harbour, where the skate was once known to live.
Mr Frusher said the skate had not been found in the deeper Bathurst channel, while the remainder of Bathurst Harbour was too shallow to be viable, particularly with increased climate variability.
"It's a very shallow ecosystem, and having spoken to experts who work in sharks and rays and skates, the most probable explanation is that we had a heating event," he said.
"And because the waters are so shallow there, that may have been what's caused them to go extinct.
Loading..."It's unlikely to be a place to release them."
Last month, state Labor MP Janie Finlay shared an opinion piece that said that while it would be "unfortunate" if the skate went extinct, they "wouldn't lose any sleep over it".
This post was "liked" by Labor leader Dean Winter.
Salmon industry-funded research by UTAS conservation ecologist Barry Brook reviewed projections of skate population decline over coming decades.
He wrote to Ms Plibersek saying that more work needed to be done over the projections, which may have been overstated.
Mr Frusher said this research did not dispute that there had been a significant decline in numbers.
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