The precariously low numbers of Maugean skates have reportedly stabilised, but the skate is still on the brink of extinction in its only home, Macquarie Harbour, the Australian Marine Conservation Society said after the University of Tasmania’s Institute for Marine and Antarctic Studies released its second interim report on the Macquarie Harbour Maugean skate population.
Salmon farming has dramatically depleted the oxygen levels in Macquarie Harbour, and oxygen levels are still desperately low despite inching up glacially this year because of a reduction in salmon biomass from its peak in 2015 along with natural oxygen recharging from sea water entering the harbour last summer.
In the deeper waters of Macquarie Harbour, oxygen levels are still not at the level where the Maugean skate can safely live, and an upturning of deep, oxygen-depleted water could spell the end of the Maugean skate in the harbour. An upturning event caused by storms in 2019 wiped out nearly half the Maugean skate population.
On the brink
AMCS Fisheries and Threatened Species Campaign Manager Alexia Wellebelove said, ‘It’s positive that the Maugean skate population in Macquarie Harbour has stabilised since 2021, but it’s not exactly cause for celebration as the Maugean skate is on the brink of extinction in its only home.
‘There are still only an estimated 40-120 mature skates left in the harbour and its extinction could be in as little as 10 years’ time, possibly earlier if a big storm creates another upturning event like the one that decimated the population in 2019.
‘It’s pleasing that there has been an increase in young Maugean skates for the first time in a decade, but they are years away from maturity and reproducing, and it doesn’t change the dangerously low oxygen levels in Macquarie Harbour.
‘Given it takes six years for these skates to reach maturity, we need to continue to do everything we can to ensure these new recruits reach breeding age to enable the species to recover,’ said Ms Wellebelove.
Salmon biomass
‘Salmon farming has dramatically depleted the oxygen levels in Macquarie Harbour, and removing salmon farming is the fastest way to improve oxygen levels for the skate to survive and recover.
‘Salmon farm stocking in Macquarie Harbour peaked in 2015 at about 20,000 tonnes. The salmon industry has not reduced biomass far enough since then, so the federal government needs to act on its own conservation advice, which recommended the removal of salmon last summer.
‘The Albanese government has made a commitment to zero new extinctions. We are calling on Environment Minister Tanya Plibersek to see that salmon farming ceases in the harbour to meet this commitment and ensure the skate’s survival.
‘Macquarie Harbour is part of Tasmania’s World Heritage Area and integral to the state’s reputation for natural beauty and conservation,’ said Alexia Wellebelove. ‘The extinction of the Maugean skate would be a devastating blow to Australia’s biodiversity and to Tasmania’s brand and natural heritage.’
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