![]() ![]() The King and Gordon rivers flow into the harbour and the flow regimes of both are altered by hydro-electric power stations.Īdded 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.Īnd historical dumping of millions of tonnes of copper mine tailings into the King river have led to high heavy metal concentrations in the harbour. "I would go on a trip, and we would catch 30 to 40 from one trip," Dr Awruch said. 'The Tasmanian tiger of the sea'Ĭynthia 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. "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 total population dropped by 47 per cent between 20.Īnother similar event to 2019 could push the species beyond the point of no return, said report co-author Jayson Semmens from IMAS.Those combined impacts resulted in a loss of up to 44 per cent of tagged individuals. 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.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. In 2022, the existence of a second population of the animals in Bathurst Harbour, around 100km south of Macquarie, was thrown into doubt.The amount of netting time needed to catch the skates significantly increased between 20.The proportion of juvenile females dropped from around 17 per cent of netted animals in 2014 to just 3 per cent in 2021.The average size of netted females significantly increased between 20. What that means is there are either significantly fewer juveniles being born, or fewer juveniles surviving.The following findings, along with a series of recent developments, has led researchers to believe the skate is at serious risk of extinction: It is used as an indication of population changes. 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). Today's preliminary report is based on a reanalysis of size-distribution data from skates netted between 2012 and 2021. Salmon farming, heavy metal pollution, changes flow regimes and climate change are all impacting Macquarie Harbour. ![]()
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