Newly hatched stingray
Jason Semmens/University of Tasmania
One of the world’s most endangered marine fish has been saved from extinction thanks to researchers who caught specimens in the wild and helped breed them in captivity.
Stingray (Zearajah Mageana) is found only in Port Macquarie, on the extremely isolated and rugged southwest coast of the Australian island of Tasmania, a region that is naturally low in oxygen, making it difficult for fish to thrive, but this is exacerbated by human impacts, particularly the alteration of river flows by salmon farming and hydroelectric dams.
Jason Semmens, from the University of Tasmania, says no one knows the exact number of rays, but their numbers have plummeted, halving between 2014 and 2021. There are now thought to be just over 1,000 individuals, and what’s most worrying is that the vast majority of rays are adults, with juveniles not reaching maturity.
As a marine heatwave raged in this area off the southeast coast of Australia last year, Semmens and his colleagues decided to make a bold intervention to save the rays from extinction.
In December 2023, the team collected 50 eggs, more than half of which hatched in captivity. They also collected four adult insects, two of which died within two weeks. The two surviving females were kept separately, so the team was shocked when the remaining female laid eggs.
That’s because rays can store sperm and fertilize the eggs, Semmens says. “On average, rays lay two eggs every four days,” he says. “We’ve seen over 100 eggs laid by rays, and the majority of them appear to be viable.”
To maximise the genetic diversity of the captive-raised young, the team is considering capturing other, already-fertilised females to obtain eggs and then releasing them back into the wild.
But David Moreno, another team member from the University of Tasmania, said captive breeding was not a complete solution, and researchers were also working to solve environmental problems in Port Macquarie, including experimenting with pumping oxygen into the water.
There is no quick fix, and even if captive-bred individuals could be released straight away, it would take four to five years for them to mature and be able to contribute to the population.
If recovery efforts fail, the cost will be huge: “This would be the first extinction of a ray or shark species in modern history,” Moreno says, “so this is a really big red line.”
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