Two alarms were sounded last year over the extinction threat that salmon farms posed to a endangered species of ray that only lives in a harbour on Tasmania’s west coast.
But there are fears that not enough has changed since, and the farms are effectively continuing as they were.
The first alarm was in May, when an Institute for Marine and Antarctic Studies (IMAS) report found that Maugean skate numbers had declined by 47 per cent between 2014 and 2021.
This was put down to reduced dissolved oxygen levels, with salmon farms considered a main source of the problem.
The second alarm was in September, when Commonwealth conservation advice urged the reduction of salmon biomass and feeding rates in the harbour by Christmas.
But at the start of 2024, dissolved nitrogen output from the farms – the Tasmanian Environment Protection Authority’s (EPA) measure of feed, which can adversely affect the harbour at high levels – increased by 14 tonnes on a rolling 12-month scale.
It then increased by another 8 tonnes by March, to 490 tonnes, approaching the new 500-tonne cap set by the EPA.
This cap was introduced in 2022, replacing a previous cap on fish biomass, which was changed after fish farms were found to be increasing their feed rates in response.
EPA Tasmania director Wes Ford said that remaining under the nitrogen limit was a positive outcome for the harbour, and believed the current salmon stock rates could be maintained.
“I’m expecting that at 500 tonnes of nitrogen, the improvements we will see will continue over the next few years, and that will allow the oxygen in the harbour to recover,” he said.
“There is a cap that [the salmon farms] operate within. As they adjust their management practices, there will be variability movement … and they’re coming off a point where they had to reduce their biomass in order to implement that cap.”
Salmon Tasmania chief executive officer Luke Martin said the industry was working “within the parameters” set by the EPA, and was exploring ways of reducing its nitrogen output.
Harbour sites ‘compliant’, but oxygen levels still vary
On Wednesday, the EPA pointed out that compliance points within 35 metres of the farms in Macquarie Harbour were compliant, an “improvement” on the previous January.
It also stated that dissolved oxygen data was “encouraging”, with deeper parts of the harbour approaching levels from before 2009, when salmon farming caused deterioration.
Dissolved oxygen is essential for the survival of the Maugean skate.
But data from the EPA shows that dissolved oxygen levels peaked in about September and then reduced by 39 per cent at a depth of 6 metres by April, and by 60 per cent at a depth of 11 metres.
These remained within the EPA’s “target range”.
Mr Ford said the long-term trend was one of improvement, however, with reduced biomass and nitrogen caps occurring in recent years.
“The data is showing improvements in both oxygen and benthic [occurring at the bottom of the harbour] impact, and that is a reflection of me having reduced the stocking density in the harbour since 2016,” he said.
“Everyone accepts that it will take a while for the harbour to restore and recover to what it was pre-2012, so we’re on a positive trajectory.”
In February, industry group Salmon Tasmania — with partial funding from the Commonwealth — began trialling the pumping of dissolved oxygen into the harbour’s depths.
Plibersek decision still being ‘delayed’
Leonardo Guida, who leads the shark conservation work at the Australian Marine Conservation Society, urged caution around any changes to dissolved oxygen levels.
“We need to tease apart the influence of natural recharging — that is, oxygen-rich seawater entering the harbour — from the influence of the oxygen pumping that’s currently going on,” he said.
“This could all change again next year because of the weather conditions.
“What we don’t want to see is that one event, like in 2019.”
In 2019, a severe storm reduced dissolved oxygen levels in the harbour, raising fears that the Maugean skate could be one severe weather event away from extinction.
Dr Guida said federal environment minister Tanya Plibersek, who is currently considering the renewal of salmon farm licences, after requests by environmental groups, needed to make a decision soon, as it had already been delayed.
Mr Martin said he believed the current measures — including nitrogen caps, monitoring and the dissolved oxygen pumping trial — had “got the balance right”.
“We feel like the level of the industry’s activity in the harbour, the way the oxygen levels have been monitored and being tracked, is now in a steady improvement and will continue,” he said.
Industry says ‘healthy’ harbour hard to define, wants ‘viable’ instead
The Tasmanian government released a conservation action plan for the Maugean skate in January, setting a range of objectives for the coming years.
A draft plan was earlier sent around to the recovery team for feedback, which includes a Salmon Tasmania representative.
A Right to Information request by the ABC shows Salmon Tasmania wanted the term “healthy habitat” altered.
“Objective 1 is to provide a ‘healthy’ habitat. That is very hard to define. Suggest changing to ‘viable’ habitat,” Salmon Tasmania technical director Matt Barrenger wrote.
The final plan had replaced “healthy” with “viable” for the first objective.
Salmon Tasmania also wanted more emphasis placed on the impacts of mining and hydroelectric dams on the harbour’s health, which resulted in marginal changes to the final document.
Mr Martin said “no-one was denying the challenges” in Macquarie Harbour.
Environmental groups say nothing has changed
Speaking on Wednesday, one year after the IMAS report, Bob Brown Foundation campaign manager Alistair Allan said governments were moving too slowly to save the Maugean skate.
“One year on, absolutely nothing has been done to remove the threats to this animal,” he said.
“Salmon farms remain in Macquarie Harbour, not a single pen has been de-stocked.”
Both the state government and the Labor opposition remain firm supporters of the salmon industry in Macquarie Harbour.
Labor leader Dean Winter spent his first day as opposition leader in the region, confirming he would stand up for salmon industry jobs.
State Resources Minister Eric Abetz said the dissolved oxygen and nitrogen levels should convince Ms Plibersek.
He was asked if the harbour was “healthy”.
“According to the standards, yes, it is,” Mr Abetz said.
“Because there are certain limits, and as I understand the science and the regulatory authorities, they’re saying that if certain levels — be it oxygen, or whatever else, nitrogen levels — are within certain parameters, then it is a tick.”
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