Salmon farmers told to destock to save endangered skate

The federal government has released a new conservation plan for the imperilled fish, with experts making it very clear that salmon farming is driving the number one threat to the species - a lack of oxygen in the waters of the harbour.

Given that it's the only place where the skate still exists, the plan urges salmon companies to rapidly destock to address the existential threat.

"... the most important anthropogenic contributor to the oxygen debt in Macquarie Harbour is ongoing salmonid aquaculture," it says.

The plan outlines urgent actions that should be achieved before the summer, which is just months away.

"Eliminate or significantly reduce the impacts of salmonid aquaculture on dissolved oxygen concentrations," it urges.

"The fastest and simplest way to achieve this is by significantly reducing fish biomass and feeding rates."

The plan says salmon stocks were reduced in 2017 and again in 2018 in response to habitat degradation.

And while there's been some improvements, present oxygen levels particularly at depths where the skate exists and where eggs can be found, remains lower than before 2009.

It was in that year that a progressive decline in dissolved oxygen levels began, coinciding with a substantial increase in salmon farming.

"There is no evidence to suggest that the small increase in dissolved oxygen concentration in Macquarie Harbour are a sustained long-term trend ... or have resulted in reduced impacts on maugean skate," the conservation plan notes, citing work carried out by Tasmania's Environment Protection Agency.

In September last year, the EPA moved to cap nitrogen output in the harbour, in order to improve oxygen levels.

"Given this new regulation focuses on only one component of the total organic carbon load from salmonid aquaculture operations, it is unknown whether this new regulation will address the known issues.

"The extent to which this new regulation has improved, or will improve, dissolved oxygen concentration in Macquarie Harbour is unknown."

Conservation groups have long pushed for an end to salmon farming in Macquarie Harbour on Tasmania's west coast.

They say the narrow-necked, fjord-like estuary is naturally poor at flushing and it's entirely unsuited for the oxygen demands and nutrient outputs of fish farming.

The new conservation plan does note that the oxygen problems might "possibly" have been compounded by hydroelectric power generation changing river flows, and the impacts of climate change.

It says efforts should urgently be made to reoxygenate the harbour's waters, possibly via mechanical means, while appropriately managing and monitoring regulated river flows in the Gordon and King Rivers.

Federal Environment Minister Tanya Plibersek has promised to ward off any new extinctions on her watch and on Wednesday promised an initial $2.1 million in federal funds to help the species.

Some of the cash will be spent on a captive breeding program to create an insurance population if it can't be saved in its wild home.

"We know the key threats remain poor water quality in Macquarie Harbour from aquaculture and hydro operations," Ms Plibersek said.

"... we urge the salmon industry and Tasmanian government to take the action needed to clean up Macquarie Harbour so the maugean skate can survive for another 100 million years."

The conservation plan sets out key goals including a substantial and sustained improvement in dissolved oxygen concentrations levels by next year, to at least the levels seen before 2009.

It says the captive population should also be in place next year.

By 2029, the goal is to have evidence of maugean skate recruitment in the harbour, and by 2041, for the number of skates - currently estimated at fewer than 1000 - to have been maintained or increased, compared to 2020 levels.

Australian Associated Press