Endangered skates saved from extinction by hatching in captivity

One of the world’s most endangered species of marine fish has been saved from extinction, thanks to researchers who captured wild specimens and helped them reproduce in captivity.

The Maugean skate (Zearaja maugeana) is only found in Macquarie harbour on the extremely isolated and rugged south-west coast of Tasmania, Australia. The area is already a naturally low-oxygen environment, making it difficult for fish to thrive, but human impacts, especially salmon farming and river flow changes as a result of hydroelectric dams, have made the situation worse.

Jayson Semmens at the University of Tasmania says while no-one knows the exact population of these skates, a collapse between 2014 and 2021 saw it halve. There may now be just over 1000 individuals, he says, and of greatest concern is that they are now predominantly adults, meaning that juveniles aren’t reaching maturity.

As a marine heatwave tightened its grip last year in this region, off south-eastern Australia, Semmens and his colleagues decided to undertake a radical intervention to try to safeguard the skates from extinction.

In December 2023, the team collected 50 eggs and saw over half of them successfully hatch in captivity. They also collected four adults, two of which died within a fortnight. The two survivors were kept separate, so the team was shocked when the remaining female laid eggs.

Semmens says this is because the skates are able to store sperm, to fertilise eggs later. “She’s been laying on average every four days, two eggs every time,” he says. “We have over a hundred eggs from her now and the vast majority of them are looking like they’re going to be viable.”

In order to maximise the genetic variability of the captive-reared juveniles, the team is considering capturing other females that have already been inseminated, obtaining eggs and then releasing the females back to the wild.

But team member David Moreno, also at the University of Tasmania, says captive breeding isn’t the full solution, so the researchers are also working to reverse environmental issues in Macquarie harbour, including a trial of pumping oxygen into the water.

There is no quick fix and even if the captive -reared individuals are able to be released immediately, it would be four to five years before they reached maturity and could start contributing to the population.

The stakes are high if the recovery effort fails. “This would be the first extinction of a ray or shark species in modern history,” says Moreno. “So it is a really big line in the sand.”

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