St Kilda mangrove die-off ‘a threat to dolphins’, expert Mike Bossley warns

The die-off of a huge area of mangroves and saltmarsh at St Kilda threatens a swath of animal species, including the Port River dolphins.

Marine biologist Mike Bossley has worked tirelessly to protect the dolphins in the Port River. Picture: Brad Fleet

A huge die-off of mangroves and saltmarsh at St Kilda could lead to Port River dolphin deaths, conservationist Mike Bossley says.

It comes as work starts to remove brine from nearby salt ponds, after leaked material was identified as a suspected cause for the dieback of at least 10ha of mangroves in the Adelaide International Bird Sanctuary and 35ha of saltmarsh.

An alliance of community and environmental groups has also formed to lobby for further action on the issue.

Dr Bossley said the mangroves and samphire saltmarsh plants provided food for organisms ranging from bacteria to plankton, fish and tiny prawns.

“The whole mass of dead mangroves at St Kilda could influence feeding habits for the dolphins in the inner port of Port Adelaide,” Dr Bossley said.

The St Kilda mangroves in South Australia are dying off. Picture: Alex Mausolf

“The amount of mangroves and samphire that have died so far probably in and of itself isn’t likely to cause the death of a dolphin. But with all of the other threats they face, and if the mangrove die-off continues to escalate … it’s adding another burden the lives of the dolphins and it certainly could and I think is likely to lead to deaths.”

Only one of the 13 Port River dolphin calves born over the past two years has survived, Dr Bossley said, and several adults had also died. While the causes of death are unknown, they face threats including pollution, being hit by boats and getting tangled in fishing lines and nets.

St Kilda resident and scientist Peri Coleman, of Delta Environmental Consulting, prepared a report on the problem for Salisbury Council in early spring last year.

The operations of Dry Creek salt fields owner Buckland Dry Creek Ltd have been in the spotlight after scenes of the dead mangroves and samphire emerged.

Conservation SA chief executive Craig Wilkins. Picture: Supplied

The EPA says it is “not known for certain” what has caused the problem, but salinity and water management in the salt fields is “an obvious focus”.

On December 24, the Energy and Mining Department issued a direction requiring Buckland to remove brine from the ponds next to the St Kilda mangroves. It also has directed the company to stop pumping water into the ponds and prevent further seepage at Para River.

Conservation SA chief executive Craig Wilkins said 15 groups on Tuesday formed an alliance to lobby for greater Government transparency over how the problem was being dealt with, the decommissioning of all salt ponds south of St Kilda, and plans to rehabilitate the area.

Consultant Peri Coleman doing testing in the region. Picture: Alex Mausolf

“We’re talking about a significant environmental damage incident that will require decades of recovery,” he said.

While the State Government estimated that about 10ha of mangroves and 35ha of saltmarsh had died in mid-September, Ms Coleman estimates the dead saltmarsh area has grown to about 100ha.

It would affect populations of animals including fish and migratory birds, she said, and remove the mangroves’ ability to sequester carbon.

Ms Coleman said after delayed action, the brine, which was crystallising, would be very difficult to remove.

A Department of Energy and Mining spokesman said the site operator was working to fix problems in the area, and government regulators were monitoring the area.

“Compliance actions as a result of the mangrove dieback remains subject to ongoing formal investigations,” he said.

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