Scientists have warned an ancient fish species that has survived since the time of the dinosaurs could be one extreme weather event from extinction after its population crashed by nearly half in seven years.
The Maugean skate, described by marine scientists as a “thylacine of the sea”, is found only in Macquarie Harbour, a vast body of water on Tasmania’s remote west coast.
Studies have found its numbers have fallen sharply over the past decade as its environment has been degraded by human influence, including from salmon farming pollution, hydro power stations altering upstream river flows and rising harbour temperatures due to the climate crisis.
These factors had contributed to a sharp drop in dissolved oxygen levels, which particularly affect survival rates in young skates. The number of surviving Maugean skate is not clear, but an interim monitoring report estimated the population had slumped by 47% between 2014 and 2021.
The decline is believed to have been hastened by an extreme event in 2019 – an “inversion” in which the water column was overturned by a westerly storm, lifting poorly oxygenated water from the harbour floor nearer to the surface. “Widespread mortalities” were found among electronically tracked skates after the event.
Scientists from the University of Tasmania said it showed rapid action was needed to prevent the species’ extinction, including funding for a captive breeding program to create an “insurance population” outside the harbour. The Australian environment minister, Tanya Plibersek, has set a goal of zero extinctions for the country’s plants and animals.
“It’s incredibly urgent because it would just take one event like we’ve seen and we may not be able to do anything [to prevent extinction],” Dr Jayson Semmens, a biologist with the university’s Institute for Marine and Antarctic Studies (Imas), said.
The leader of the monitoring program, Dr David Moreno, said few juveniles were coming through to keep the population viable. “What’s happened is that in the past 10 years or so we have seen a massive decline in dissolved levels of oxygen deep in the harbour; that hasn’t improved and it’s now chronic,” he said. “We risk losing an important species.”
The scientists called for a curb on activities managed by the Tasmanian government that could affect the skate, including fish farms, recreational fishing and changes in river flow from upstream dams. They also said funding was needed to extend the monitoring project, which began in 2012 and is due to end this year.
The health of Macquarie Harbour, an area about six times larger than Sydney Harbour, plummeted last decade after a significant expansion of salmon farming was approved in 2012 despite warnings of potential impact on marine life. The cap on fish farm production was later lowered back to near pre-expansion levels. The health of some species improved, but oxygen levels did not rebound.
The Maugean skate lives to about 10 years of age, mostly in a layer of brackish water between 7.5 and 12.5 metres deep between surface freshwater that flows from the Gordon and King rivers and saline bottom water from the Southern Ocean.
It was discovered in Bathurst Harbour, in Tasmania’s deep south-west, in 1988, but only four specimens were seen there and none since 1992. A DNA study last year suggested the species was likely now restricted to Macquarie Harbour.
A 2016 study suggested about 3,200 remained, though that figure was later described as a broad estimate. The Tasmanian Inquirer reported that Dr Neville Barrett, a Imas marine scientist, last year told a public event that he believed the species was likely to be extinct within a decade on its current trajectory.
The federal government’s threatened species scientific committee will assess next month if the skate should be listed as critically endangered, up from endangered, after receiving a submission from conservation groups. It was included last year on a list of 110 priority species for government action over the next decade.
The Australian Marine Conservation Society and Humane Society International called on the government to do “everything in its power” to avoid an extinction. Dr Leonardo Guida, from the Australian Marine Conservation Society, said the species had “been around since Tyrannosaurus rex roamed the Earth” but was now being “choked to death in its home”.
“Tasmania is home to Australia’s most infamous extinction, that of the thylacine or Tasmanian tiger,” he said. “Does the state really want the ignominy of hosting the world’s first extinction of a shark or ray in modern times due to human activity?”
A spokesperson for Plibersek said Labor did not accept extinctions as inevitable, “unlike the previous government”. “It’s important we do what we can to understand the threats to species and use the most-up-to-date advice to better protect them,” the spokesperson said.
The Tasmanian government referred questions about the study to the state’s Department of Natural Resources and Environment. A department spokesperson said it provided substantial support for research into the skate and was working with stakeholders on its conservation.