- Tasmania's EPA says increased rainfall responsible for over Macquarie Harbour's falling oxygen levels, ignoring impacts of salmon farms
- Foreign-owned salmon companies could cut salmon numbers to save Maugean skate and its long-term future
- Low oxygen levels leave Maugean skate vulnerable to an extreme weather event, such as the "upturning" that wiped out an estimated half of the skate population in 2019
Oxygen levels have fallen further in Macquarie Harbour, the endangered Maugean skate's only home, since the Australian Government changed the federal nature laws to allow salmon farming to continue in the harbour, the Australian Marine Conservation Society (AMCS) said after Tasmania's Environment Protection Authority released the oxygen data today.
The Maugean skate is facing extinction primarily because of low dissolved oxygen in Macquarie Harbour since intensive salmon farming started in the harbour.
The EPA's analysis shows dissolved oxygen in Macquarie Harbour from June 2025 to July 2026 has declined to levels worse than those between December 2023 to November 2024 - just before the Australian Government changed the nature laws in March 2025 to allow salmon farming to continue there. Oxygen has declined at the depths preferred by the skate at 5-15 metres, and concerningly, levels below 15m depth have fallen below 40% dissolved oxygen. With a hot summer predicted, that leaves the skate vulnerable to environmental conditions that wiped out half the population in 2019. The EPA cited greater than average rainfall in the area, ignoring the impacts of salmon farming.
In 2019, oxygen-depleted water, caused primarily by intensive salmon farming, rose from the depths of the harbour, choking skates in their habitat. The oxygen-depleted bottom waters also prevented skates from diving deeper to escape surface waters that warmed to above 20 degrees Celsius during parts of 2019. Salmon farming continues unabated despite scientific recommendations to reduce it, and now there are renewed fears another storm event could decimate the skate population, making extinction inevitable.
AMCS shark expert Dr Leonardo Guida said: "We are back where we started when we first highlighted the extinction risk of the Maugean skate, with low oxygen levels in the skate's only home, Macquarie Harbour. No one can control the weather, but the salmon industry and the regulators can control the amount of salmon kept in Macquarie Harbour.
"Salmon stocks have not dropped enough nor quick enough to build resilience in the harbour, and the foreign food giants who own the salmon farms have not shown any willingness to cut salmon numbers since the plight of the Maugean skate came to light.
"Maugean skate numbers have not improved enough for the population to survive another extreme weather event in Macquarie Harbour. With a hot summer on the horizon, skates will try to retreat to deeper water to escape warmer surface waters, but this may not be possible. They risk being cooked at the top and choked from the bottom - a possible repeat of the 2019 conditions that wiped out half the Maugean skate population.
"More than $20 million of taxpayers' money was used to pump oxygen into the harbour's water using what is effectively a giant soda syphon, but with a change in the weather this has failed to increase oxygen levels. So far, the skate has been lucky that there have been natural injections of fresh oxygen-rich seawater into the harbour - but that luck looks to be running out.
"Pumping oxygen into the water alone is not enough to repair the damage already done by at least decade's worth of industrialised salmon farming and tens of thousands of tonnes of salmon defecating in the harbour. Salmon have to be removed from Macquarie Harbour, so it has enough dissolved oxygen to support the recovery of the Maugean skate.
"With the endangered Maugean skate struggling to survive in its only home, Tasmania is on the brink of having its highest profile extinction since it drove the Tassie tiger off the planet. Tasmanian produce trades on the state's reputation for its relatively pristine and wild natural areas, and another extinction would heavily damage that reputation."
