Huge leatherback turtle washes up on Pennington Bay beach on Kangaroo Island

A huge leatherback turtle washed up on Pennington Bay beach on Kangaroo Island this week, dead but largely intact.

According to Wikipedia, the leatherback sea turtle is the largest of all living turtles and the heaviest non-crocodilian reptile, reaching lengths of up to 2 metres and weights of 600 kg.

Sadly, recent estimates of global nesting populations are that as few as 26,000 females nest annually, which is a dramatic decline from the 115,000 estimated in 1980.

The Dawe family from the Adelaide Hills was visiting friends on Kangaroo Island and were amazed on their second beach visit of the trip to find the big turtle.

Mum Krystina said she estimated the turtle to be around 1.5 metres long and it was located on the beach halfway between the stairways at Pennington. They spotted it on Tuesday, Jan. 11.

"It was amazing and not something we expected to see, I guess a once in a lifetime experience," she said.

The beach will be forever known as "Turtle Beach" for the Dawe and Milbank families.

In between the sightseeing, Krystina did call several authorities, including the local council, to try and alert them to the unusual discovery.

The families returned the next day, and from the clifftop they could see that the shape of the turtle had changed significantly.

Tony and Phyl Bartram from KI/Victor Harbor Dolphinwatch, who live nearby, also took photographs of the by now badly decomposed turtle, sending a report to the SA Museum.

OVERNIGHT DAMAGE: The leatherback turtle one day later on Wednesday showed significant signs of decomposition possibly from rolling around in the surf, or even sharks. Photo: Dawe family

OVERNIGHT DAMAGE: The leatherback turtle one day later on Wednesday showed significant signs of decomposition possibly from rolling around in the surf, or even sharks. Photo: Dawe family

While the Dawe family suspected someone may have cut off the shell as a souvenir, an expert having looked at the photos believes it is more likely that the damage was done by rolling around in the surf overnight or possibly even sharks having a feed.

Honorary researcher at the SA Museum, Mark Hutchison said the shell may have burst from the gases and even in Tuesday's photos when the carcass was more intact, the fins did look decomposed, as if it had been floating around the ocean for some time.

He said leatherback turtles unlike all other turtle species did inhabit colder non-tropical waters.

The leatherback is found in all tropical and subtropical oceans of the world, and its range extends well into the Arctic Circle.

While they do need to breed and lay their eggs in tropical waters, they did regularly migrate through South Australian waters, and were found occasionally washed up, he said.

Leatherback turtles were particularly vulnerable to ingesting plastic given their feeding habits of eating jellyfish and other floating animals, but boat trikes and fishing gear entanglement was also a common cause of mortality, he said.

The kids in the Dawe and Milbank families were consoled that the turtle initially did not have signs of injury or entanglement, so perhaps "it died of old age".

Krystina said the kids on the way over had made a list of animals they wanted to see, but they never thought they would see a turtle.

For the record, they were able to tick off every animal, except a goanna, even seeing a shark swimming around Weirs Cove near Admiral's Arch.

Meanwhile, more from the SA Museum's Mark Hutchinson:

Leatherbacks regularly cruise through SA's waters, but each year one or more is accidentally killed, typically in one of three sorts of accidents: collision with a ship or its propeller, fouled and drowned in discarded gear, or death from ingesting discarded plastic bags or sheeting.

If the last cause sounds peculiar it's because leatherbacks are specialised feeders on jellyfish and salps (floating colonial sea squirts), and they apparently mistake the translucent drifting plastic as something edible.

They die at sea and decay starts, then the body floats ashore. Each of these deaths is a significant loss to the species, and collectively probably a major reason why their global population is on a steep decline.

Adult leatherbacks have long life expectancies - estimates are up to 80 years or more - during which time, females will produced many thousands of eggs.

This is necessary given the massive juvenile mortality that is normal for sea turtles of all sorts.

The species survives by ensuring enough eggs are laid, and so too many adult deaths means not enough eggs.

Sea turtles of other species (green, loggerhead and Ridley) also wash up dead on our beaches, but these are victims of wandering too far from their tropical waters.

Water temperatures off Australia's south coast fall too low to allow these other species to survive for very long.

But leatherbacks are adapted to living in cold water, and can safely come here during their non-breeding period (a bit like migratory birds) before heading for their tropical nesting areas every couple of years to get the next crops of eggs laid.

Thanks for your interest in these gentle and rather mysterious giant reptiles, part of Australia's coastal fauna that few people get to encounter.

There is some follow up, and I've asked the KI Wildlife folks if a tissue sample can be collected and stored in the Museum's biological tissue collection.

It will then be available for any researchers who need DNA information on the body, potentially adding to the info available about genetic diversity in this species, and perhaps pointing to the source population from which it came.

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