Maugean skate threatened with extinction

In an article in the Mercury, 23 May 2023, Peter Boyer reports that the survival of a vital Tasmanian fish is seriously threatened, but says we can take action now. He writes (our emphases):

Everything that lives will die, sooner or later. We have no option but to accept this simple reality. But that doesn't mean we should accept the death of a whole species.

That's what hangs over the maugean skate. At about 75cm long and 50cm wide, it is Tasmania's largest endemic fish. It is also the last of its kind. Emerging as a species over 60 million years ago, it now lives only in Tasmania's Macquarie Harbour.

Last October, federal Environment Minister Tanya Plibersek launched her new "Towards Zero Extinctions" policy. The policy's 10-year threatened species action plan lists the maugean skate as a key species to be preserved. "We don't accept that environmental decline and extinction is inevitable," Plibersek said.

Brave words. Australia's abysmal record in preserving its biodiversity, effectively acknowledged in Plibersek's policy document, includes the elimination of 100 species since colonisation in 1788, as a result mainly of habitat loss and introduced predators.

Broader ecological health was a key factor in the plan's focus on 20 key conservation locations and 110 priority species of plants and animals, seeking "flow-on benefits" to other threatened species in the same habitats. In that priority list were 12 Tasmanian species, all but one of them occurring only here and most in critically low numbers.

Identified as a species in 1988 and listed as endangered in 2004, the maugean skate hit the news back in 2011 when the salmon industry itself admitted that a big expansion it was planning would cause what it called "minimal to moderate" harm to the species.

In succeeding years, while the salmon industry was ramping up its pressure to expand in Macquarie Harbour, the Tasmanian public was repeatedly warned by scientists that this posed real ecological threats, especially to the skate.

In 2013, the scientist who first described it, Graham Edgar, said that its very limited habitat made it especially vulnerable, while Neville Barrett from Hobart's Institute of Marine and Antarctic Studies said expanded fish farming risked its future. That and further warnings from biologists and ecologists over successive years were met with government and industry assurances that the matter was in hand.

In 2016, the Environment Protection Authority reported "worryingly low" levels of dissolved oxygen and sea floor dead zones up to 500m wide around pens. Then, in 2017, came news that harbour fish, including 1.35 million salmon, had died from low oxygen and summer heat stress. Responding to outraged critics, the government said it would be guided not by "green front groups" but by "expert research".

A research outcome that the government isn't talking about, released last week by scientists from the Institute of Marine and Antarctic Studies, shows that numbers of the maugean skate dropped by nearly half between 2014 and 2021. What really rang alarms was sampling data indicating that between 2014 and 2021, the proportion of juvenile females in the total population had crashed by more than 82 per cent.

Leaders of the survey, David Moreno and Jayson Semmens, said last week that the data outcome implied the need for "immediate action". Last week, Plibersek's office revealed that the maugean skate's conservation status may be upgraded from endangered to critically endangered when the relevant committee next meets in June.

That should focus government and industry minds. Salmon farming is identified as a principal cause of the species' plight, whereby fish faeces and uneaten food piled on the harbour floor under and around salmon pens – 2000 tonnes of it each year – lowers dissolved oxygen levels throughout the harbour. The other human agent is overfishing.

Drastic measures are needed, says water quality expert Christine Coughanowr. She proposes immediately destocking salmon and ocean trout leases, banning recreational gill netting in Macquarie Harbour, and working with Hydro Tasmania to increase inflow of oxygen-rich Gordon River water.

Current environmental licences for farming leases are due to expire in November. Coughanowr and the Tasmanian Independent Science Council are urging Tasmania's Environment Protection Authority not to renew licences until oxygen levels have recovered and the maugean skate shows clear evidence of recovery.

Before, during and since the 2017 fish death crisis, the Tasmanian government ignored proposals for a genuinely sustainable, science-based Macquarie Harbour salmon industry based on the health of the broader environment in which it operates. In its zeal for what it calls "sustainable growth", the government is killing the goose that lays the golden egg.

Premier Jeremy Rockliff's current passion is a sports stadium offering pleasure for moments in time. The survival of species is a matter for the ages. The end of the maugean skate will diminish us all.

Peter Boyer is a former Mercury reporter and public servant who specialises in the science and politics of climate.