The Maugean skate, a prehistoric ray found only in Tasmania's Macquarie Harbour, is teetering on the brink of a 'catastrophic' extinction, and the primary culprit identified is salmon farming. This ancient species, a relic from a bygone era, faces an existential threat, with scientific advice pointing a clear finger at industrial aquaculture as the main stressor on its delicate habitat.
But here's where it gets controversial... The very method used to count these elusive creatures has been a source of scientific debate. Early estimates in 2023 suggested a dramatic population crash, painting a grim picture of extinction by 2050. However, subsequent estimations showed a baffling, almost unbelievable, surge, highlighting the unreliability of the data. Professor Jayson Semmens of the Institute for Marine and Antarctic Studies acknowledges this challenge, stating, "As a scientist, there's all this scrutiny on us from all these different angles. Trends go up and down all the time, and when you look at something at a point in time, it often doesn't tell you what you need."
This very uncertainty around the numbers played a crucial role in the Commonwealth's decision not to upgrade the Maugean skate's status from 'endangered' to 'critically endangered,' despite a draft recommendation in 2024 to do so. Yet, one factor has remained constant across all reports: the devastating impact of salmon farming.
The Commonwealth Threatened Species Scientific Committee's final report is unequivocal: industrial aquaculture is the primary driver of habitat stress for the Maugean skate.
How exactly does salmon farming wreak havoc on this ancient ray?
The Maugean skate prefers the calmer, oxygen-rich waters found at depths of five to 15 metres in Macquarie Harbour. While it can typically weather the natural seasonal dips in dissolved oxygen, a prolonged reduction is lethal. This is precisely what occurred between 2009 and 2014, a period that coincided with a significant expansion of salmon farming operations.
The mechanism at play is organic carbon. While river inflows contribute organic carbon, most of it floats on the surface. Salmon farm waste, however, is far more bioavailable and is released directly into the mid-waters, which already have lower dissolved oxygen levels. This waste then sinks, accumulating in deeper layers and creating an oxygen-depleted zone that is toxic to the skate.
And this is the part most people miss... The Commonwealth's advice starkly states: "The Maugean skate in Macquarie Harbour is now suspected to be at or possibly beyond the limits of its tolerance of environmental change. The consequence of reduced water quality due to salmonid aquaculture operations would be catastrophic… particularly when considered with cumulative impacts of other threats."
This makes salmon farming the "most important anthropogenic contributor" to the dissolved oxygen crisis. Other factors, such as dams impacting river flows, historical mining, and rising water temperatures, exacerbate the problem, but the report clearly identifies aquaculture as the primary antagonist.
The risk matrix within the advice leaves no room for doubt. Under 'catastrophic consequences' and 'almost certain likelihood' sits: "Reduced water quality from salmonid aquaculture operations in Macquarie Harbour."
So, are the mitigation measures actually working?
It's not as though no changes have been made. The Tasmanian Environment Protection Authority (EPA) has progressively reduced the allowed fish biomass, from 21,000 tonnes in 2017 down to 9,500 tonnes by 2020. In response, fish farms increased feed levels, leading to nitrogen issues, which then prompted nitrogen output limits in 2022 and oxygen mitigation plans in 2023.
These efforts have shown some positive signs. The Commonwealth advice notes "a reduction in organic matter inputs and some improvements to sediment health." Data from September 2024 suggests that dissolved oxygen levels might be improving at certain sites due to reduced salmon biomass. However, the full extent of this improvement is still under investigation.
Furthermore, the Commonwealth is funding a trial reoxygenation program, essentially pumping oxygen bubbles into the harbour via a barge. While this technology could improve oxygen levels and aid skate conservation, it's still in its experimental phase, and its effectiveness and scalability remain uncertain.
What the independent science committee does believe will make an immediate difference is a significant reduction in salmon farming over the next 12 months. This is listed as the top short-term action: "Eliminate or significantly reduce the impacts of salmonid aquaculture on dissolved oxygen concentrations." The simplest way to achieve this, they state, is by "significantly reducing fish biomass and feeding rates." This advice has been consistent since 2023.
Environment Minister Murray Watt has stated he will adhere to the scientific advice. "It's not for me to quibble with the advice of independent scientific experts," he said, confirming that the updated conservation advice will be followed. Whether this includes the crucial recommendation to reduce fish biomass remains to be seen.
Anne Urquhart, a Labor member known for her advocacy for salmon farm jobs, has deferred the decision to Minister Watt, stating, "At the end of the day, Minister Watt will make decisions based on what the science is, and what advice he gets from the department."
This situation raises critical questions: Given the clear scientific consensus on the catastrophic risk posed by salmon farming, should the government prioritize the immediate reduction of fish biomass to save the Maugean skate, even if it impacts jobs? Or are the current mitigation efforts and the potential of new technologies sufficient to balance conservation with industry needs? What are your thoughts on this delicate balance?
