Four of the world's largest sea turtles that are rarely found close to Australian shores have washed up on the NSW Central Coast over the past couple of weeks, in what experts have described as concerning and unusual.
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The latest endangered leatherback turtle to be found was on Sunday at North Shelly Beach.
Between March 27 and April 1, the pelagic turtles were also found at Toowoon Bay/North Shelly, Avoca, and Birdie beaches.
Founder of Australian Seabird and Turtle Rescue Central Coast Cathy Gilmore said volunteers were called out to the strandings.
"We are all really devastated but yet we are all really fascinated," the wildlife rescuer of 30 years said.
"They are the biggest species of turtle. These guys can dive deeper than some whales can, that's pretty amazing.
"They very rarely are near … Australian shores."
James Cook University marine biology professor Mark Hamann said it was "very unusual" to have so many washed up in a restricted geographic area.
"I think it's pretty concerning because we don't have a very good situation for leatherbacks in the Pacific Ocean," he said.
"The other thing that worries me is that we don't know the proportion of affected turtles that wash ashore so perhaps there's more out there that were affected."
What's the cause?
NSW National Parks and Wildlife Service said the Australian Registry for Wildlife Health has undertaken necropsies, where possible, to better understand why the turtles may have died.
"While it is unusual, it is possible that the recent storms have played a part in their washing ashore," the spokesperson said.
"During storms and high swells there is an increase in carcasses washing ashore on local beaches."
The Australian Museum has collected a skull to help better understand leatherbacks.
Professor Hamann said other threats included fisheries bycatch and consuming plastics that looked or smelt like jellyfish.
"Things like soft plastic bags, bag fragments, other plastic fragments; they'd be searching them out," he said.
"Perhaps the currents or the eddies have spun up in a circular motion and aggregated a bunch of plastic; whether that's from the floods or pre-existing.
"It's not possible to attribute it definitively to the floods but the floods have added considerable plastic and other things to the oceanic environments."
Ms Gilmore said she hoped lessons could be learnt.
"They're really special animals and we need to know what's happening so that we can maybe help fight and fix."
