Environment minister Tanya Plibersek's target of preventing any new extinctions of plants and animals is headed for failure without swift intervention, scientists warn.
Researchers from the Institute for Marine and Antarctic Studies (IMAS) said a single extreme weather event could be enough to push the species some call the "Tasmanian tiger of the sea" to the brink of extinction.
The maugean skate (Zearaja maugeana) is a species of ray endemic to Macquarie Harbour on Tasmania's west coast, and has a Gondwanan lineage that dates back to the Cretaceous more than 66 million years ago.
The endangered skate's population almost halved between 2014 and 2021, and there's no sign the drivers of the decline have eased, according to a report published today by researchers at the University of Tasmania's IMAS.
While the skate monitoring project will continue as planned until the end of the year, the team decided to fast-track today's interim report.
"This is really unusual. Usually you hold off until you have the full study and you analyse it," said report co-author David Moreno.
"We think that the urgency of the numbers warranted having something out there that we can use for informing managers."
The researchers are recommending a raft of measures including a captive breeding program be implemented in order to avoid extinction.
"The situation is dire enough that, first of all, we need to start considering ex-situ conservation options," Dr Moreno said.
Today's preliminary report is based on a reanalysis of size-distribution data from skates netted between 2012 and 2021.
That was combined with an analysis of the rate at which the animals were able to be caught, known as catch per unit effort (CPUE). It is used as an indication of population changes.
The following findings, along with a series of recent developments, has led researchers to believe the skate is at serious risk of extinction:
- The average size of netted females significantly increased between 2014 and 2021. What that means is there are either significantly fewer juveniles being born, or fewer juveniles surviving.
- The proportion of juvenile females dropped from around 17 per cent of netted animals in 2014 to just 3 per cent in 2021.
- The amount of netting time needed to catch the skates significantly increased between 2014 and 2021.
- In 2022, the existence of a second population of the animals in Bathurst Harbour, around 100km south of Macquarie, was thrown into doubt. An environmental DNA analysis of Bathurst Harbour published last year found no evidence of an established population there. The existence of that second population was thought to provide a buffer against the species' extinction. A total of four skates have been found in Bathurst Harbour since the species was discovered there in 1988, but it's now thought that if there ever was an established population there, it has since disappeared.
- Earlier monitoring of the skate in Macquarie Harbour found it suffered two big crashes in 2019: a pulse event, known as an inversion, and a second warm-water event which caused severe oxygen depletion in deeper water. Those combined impacts resulted in a loss of up to 44 per cent of tagged individuals.
- The total population dropped by 47 per cent between 2014 and 2021.
Another similar event to 2019 could push the species beyond the point of no return, said report co-author Jayson Semmens from IMAS.
"The environmental changes in the harbour have increased the skate's vulnerability to sudden high-impact events, such as water column turn-over driven by westerly winds, which can happen at any moment and potentially decimate the population," Dr Semmens said.
'The Tasmanian tiger of the sea'
Cynthia Awruch, a skate researcher from the University of Tasmania who wasn't involved with today's report, said it was getting harder to find the animals.
"I would go on a trip, and we would catch 30 to 40 from one trip," Dr Awruch said.
"Now we go and all week, we're intensive netting, and they're just not there."
The IMAS researchers said the skate was dying a "death of a thousand cuts".
Dissolved oxygen levels in the harbour have declined significantly since 2009, and "show no sign of recovery", Dr Moreno said.
Low dissolved oxygen is thought to be contributing to poor survival of juveniles, which are more susceptible to environmental change.
Dr Moreno said there were several sources causing the lower dissolved oxygen in Macquarie Harbour, including salmon farming.
"There are a few different things that affect oxygen dynamics in the harbour. One of them is the expansion of aquaculture — aquaculture has a direct role in the oxygen budgets in the harbour.
"The other component of it is freshwater flows into the system. Water flows play a very, very big role in the mixing dynamics," he said.
The King and Gordon rivers flow into the harbour and the flow regimes of both are altered by hydro-electric power stations.
Added to that, climate change has warmed the deeper water in the harbour by between 1.5 and 2 degrees Celsius over the past 30 years and as water warms, it holds less dissolved oxygen.
And historical dumping of millions of tonnes of copper mine tailings into the King river have led to high heavy metal concentrations in the harbour.
The Australian Marine Conservation Society (AMCS) and Humane Society International Australia have lodged a joint-submission Threatened Species Nomination with the Department of Climate Change, Energy, the Environment and Water to have the skate's listing upgraded from endangered to critically endangered.
Leo Guida from AMCS said Ms Plibersek risked "falling at the first hurdle" in her pledge for no new extinctions, and he's calling on her to immediately intervene to assist in the recovery of the skate.
"Given that she's made the ambitious and commendable commitment to no new extinctions, we want her to ensure that the harbour is restored to health so that oxygen levels are conducive to the survival and recovery of the skate," Dr Guida said.
"To do this requires an immediate rest of salmon aquaculture, and also that the river flows for the production of hydro-electricity are managed for their downstream effects on the harbour."
Dr Guida said that if the Tasmanian and federal governments didn't act now, there would be a "marine extinction on our watch". He described the skate as the "Tasmanian tiger of the sea".
"I affectionately call it a 'dinosaur in a bathtub'. It's a living dinosaur, and Macquarie Harbour is an enclosed space where it lives, in probably an area of a hundred square kilometres or less.
"And this bathtub has had everything thrown at it: historic mining impacts, climate change, aquaculture, the works."
Response will set a precedent
Dr Awruch said a captive breeding program needed to be part of the recovery process, but even then it was not guaranteed to work.
She said there were great difficulties in breeding captive individuals and without remediation of their habitat, returning them to the wild was futile.
"If they don't stop the pollution in the area, there's no chance that the animal will survive. Even if they do stop the pollution in the area, I don't know the chances of the animals surviving.
"I want to be positive but I doubt it. I think that the animal is just dying slowly."
A spokesperson for Minister Plibersek said the "Tasmanian government has primary responsibility for managing aquaculture and river flows" in Macquarie Harbour.
The spokesperson confirmed the federal government had received a nomination to uplist the skate's status from endangered to critically endangered.
"The Threatened Species Scientific Committee will assess the nomination at its meeting next month and will then make a recommendation to the minister."
In the meantime, the federal and Tasmanian governments are working on a range of projects aimed at conserving the skate, according to the spokesperson.
In response to questions from the ABC, the Tasmanian Environmental Protection Authority said it had "reduced aquaculture by limiting the amount of feed that can be put into the harbour".
"The new limit is a 10 per cent reduction on the amount of feed used in 2021. This means that allowable feed inputs are similar to inputs in 2019," the spokesperson said.
"The EPA is confident that this regulatory tool will limit finfish production in Macquarie Harbour, and therefore build upon improvements in ecosystem function and dissolved oxygen levels that have been observed in Macquarie Harbour since 2017."
A spokesperson for the Department of Natural Resources and Environment Tasmania said it was engaging in a range of actions to help prevent the skate's extinction.
"The Department of Natural Resources and Environment Tasmania (NRE Tas) provides substantial funding and in-kind support for research into the maugean skate, and is actively engaging with key stakeholders on a range of proactive and precautionary actions to minimise threats to the maugean skate, identify research and monitoring priorities, and determine short and long-term management and conservation actions needed to recover the skate.
Among the measures being looked at is a captive breeding program, the spokesperson said.
"[One measure includes the] formation of technical and scientific working groups to look at the potential impacts of industry, pollution and predation, and identify captive breeding or reintroduction opportunities.
"The working groups include scientific experts from the Institute of Marine and Antarctic Studies (IMAS) and CSIRO, industry stakeholders, Hydro Tasmania, and representatives from the Australian Government's Department of Climate Change, Energy, the Environment and Water (DCCEEW)."
A response was not received from the Department of Climate Change, Energy, the Environment and Water by deadline.
Dr Guida said the government's actions here would set a precedent for other endangered species.
"These same threats of exploitation of natural resources, fishing impacts, climate change, are having the same adverse effects on other endemic sharks and rays that are at high risk of extinction in our south-eastern waters of Australia.
"So what we do here is going to be a litmus test of how we go about conserving our oceans into the future and acknowledging the conservation risks and extinction risks that are right before us."
