Scientists advising the Australian government on how to save the threatened Maugean skate from extinction have recommended the salmon industry be either scaled back dramatically or removed from Tasmania’s Macquarie Harbour after finding fish farms are the greatest threat to its survival.
The advice is included in a conservation report by the government’s threatened species scientific committee that says the skate – an ancient ray-like species found only in the harbour in the state’s west – should be considered critically endangered.
The committee estimated there were between 40 and 120 adult skates remaining in the wild, numbers it described as “extremely low”, and that this was projected to fall by 25% in the next generation. The population was cut roughly in half over the past decade.
Its advice landed as the federal environment minister, Tanya Plibersek, was reconsidering the future of salmon farm licences in Macquarie Harbour after environment groups made a legal case that an industry expansion in 2012 had not been properly approved.
The recommendation the industry should be cut back is likely to draw a sharp response from the Tasmanian Liberal and Labor parties, which both strongly back the $1.3bn industry. Macquarie Harbour produces only about 13% of Tasmanian salmon, but industry supporters argue it is an important hub and employer on the state’s remote west coast.
In May, the Liberal premier, Jeremy Rockliff, and Labor opposition leader, Dean Winter, signed an open letter organised by lobby group Salmon Tasmania urging the Albanese government to “end the uncertainty” and deliver a “positive decision” for the industry. The letter did not mention the skate and accused the federal government of responding “to pressure from environmental activists”.
The threatened species committee report said the main threat facing the species was degraded water quality, primarily due to “substantially reduced” levels of dissolved oxygen across the harbour, a third of which was within a world heritage area.
Previous studies have said the problem was caused by fish farms, hydro power stations altering upstream river flows, gillnet fishing and rising temperatures due to the climate crisis.
But the committee cited evidence that the salmon industry was the most important human contribution to the drop in oxygen, and repeated a previous finding that failing to deal with it could be “catastrophic”.
It said the highest priority to prevent the skate’s extinction in the wild was to “eliminate or significantly reduce the impacts of salmonid aquaculture on dissolved oxygen concentrations. “The fastest and simplest way to achieve this is by significantly reducing fish biomass and feeding rates,” the report said.
It echoes advice from the committee a year ago that called for urgent action including reducing the amount of salmon before last summer. Its latest report also recommended trying to mechanically improve dissolved oxygen levels, better management of the flow of the Gordon and King rivers into the harbour and a captive breeding program for the species.
Some of that has begun. The University of Tasmania’s Institute for Marine and Antarctic Studies (Imas) this week announced the hatching of the first baby Maugean skate from an egg laid in captivity. The captive breeding program has also produced about 25 hatchlings from wild-laid eggs that were transferred from the harbour to a tank in Hobart.
A $7.2m industry and government-funded trial is under way pumping reoxygenated water from a barge to 30 metres below the harbour surface. Plibersek has described it as a “positive step forward”, but said “on its own, it will not be enough to solve the problem”.
The threatened species committee has called for public submissions before 26 September on whether the skate’s listing should be upgraded from endangered to critically endangered.
Plibersek said that decision was separate to the reconsideration of salmon farm licences in Macquarie Harbour, which began in November last year and was ongoing.
The state Environment Protection Authority approved a substantial expansion of the industry in the harbour in 2012 but was forced to cut allowed fish numbers in 2017, 2018 and 2020 as the health of the waterway plummeted. The fish biomass limit was now about a third of what was approved 12 years. An EPA report this year found oxygen levels had “shown recent signs of improvement”, but had not returned to pre-2010 levels.
On the reconsideration, a spokesperson for Plibersek said the government was “carefully considering the information and the scientific advice that it has obtained to ensure a proper, legally robust decision”.
“People on all sides of this debate, including industry and environmentalists, would agree that it’s important this decision is legally sound and based on sound evidence,” the spokesperson said. “The government is acting in accordance with the best advice, including legal and scientific advice.”
