A remote harbour where the future of salmon farming is under a cloud because of risks to an endangered fish is showing continued improvements in water quality, a regulator says.
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But a conservation group says the latest data for Macquarie Harbour on Tasmania's west coast is not as rosy as claimed.
Federal Environment Minister Tanya Plibersek is reviewing aquaculture approvals granted in the harbour after green groups' concerns.
They're worried waste from the farms and reduced oxygen levels are pushing the Maugean skate, which only lives in the harbour, to extinction.
A federal government committee recommended urgent action before last summer, noting a significant correlation between reduced dissolved oxygen levels and increases in salmon aquaculture.
Tasmania's Environment Protection Authority said data, released on Thursday, showed a clear trend of improving oxygen levels in the middle and deeper waters of the harbour.
"The dissolved oxygen levels are now close to the range observed prior to 2010, when the levels began to decline," authority director Wes Ford said.
Data pointing to water quality improvements released by the authority in May was critiqued by environmentalists as being the result of a one-off influx of water.
Mr Ford said the latest data didn't take into account a major "recharge" event in May.
The salmon industry is also undertaking a trial in which oxygen is pumped into the harbour from a barge.
"The ... oxygenation project has not yet reached its full scale and is unlikely to have had a significant impact upon oxygen levels across the harbour," Mr Ford said.
But Environment Tasmania said they remained concerned oxygen levels in the skate's habitat in the harbour's centre and southeast remained in a "red zone".
"Improvements have been seen within the northwest section of the harbour closest to ocean," campaigner Rebecca Howarth said.
"Low oxygen remains an issue in the southeast World Heritage area ... suggesting a correlation with oceanic recharges that occurred in 2021 and over the last several months."
Mr Ford said further improvements in water quality were expected because companies were required to use oxygenation equipment post-trial or lessen their oxygen demand.
Dissolved oxygen levels in the harbour remain below pre-2010 levels.
The state Liberal government, which supports aquaculture continuing in the harbour, and industry body Salmon Tasmania said the data was proof regulation was working.
"The Tasmanian government firmly believes that the Maugean skate and the salmon industry can continue to co-exist," Environment Minister Nick Duigan said.
Millions of dollars have been spent on a skate recovery project which includes a captive breeding program.
Salmon farming in the harbour peaked in 2014/15 when the biomass of operations was more than 20,000 tonnes.
Since early 2017, the maximum biomass has been progressively lowered and has in recent years been capped at 9500 tonnes.
Australian Associated Press
