Piles of crab exoskeletons have been discovered sprawled across two kilometres of Cooks Beach at Freycinet.
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This is not an unusual find, according to IMAS professor Caleb Gardner.
The giant spider crabs form mounds to moult their shells, and when there is a big swell, they wash ashore in clusters, he said.
“They’ve got a little line along the side of their shell, which splits open when they’re going to moult, and that makes it easier for the crab to emerge.
“That line only splits if they’re moulting. If the crab is just dead, they fall apart in a different way, so to me it looks very much like moulted crabs.
“You can sort of see inside the shell - they were nice and clean inside the shell.”
Professor Gardner said crabs shedding their exoskeleton was like snakes outgrowing and shedding their skins.
“Crabs are naturally very social and they often tend to moult at the same time anyway.
“So then you get these social crabs that will sit and harden up, which takes maybe half-a-day to get strong enough until they can walk around again, and off they go leaving all their old shells behind, which will roll around in the surf.
“Then, if you get a good swell or something, they’ll get washed up on the beach just like seaweed or other shells in the sea.”
Professor Gardner said these aggregations occurred all the time in Tasmania so you can get crabs washing up on beaches any time of the year.
“There are records of it happening here for hundreds of years.”
The crab exoskeletons follow the discovery of dead birds and fish on East Coast beaches earlier this year.
In February, more than 20 dead penguins and cormorants were found washed up at Greens Beach and West Head Beach.
Experts believed natural season and environmental influences were the likely cause of the birds’ deaths.
In April, hundreds of dead tropical fish were discovered on East Coast beaches.
They washed ashore after being pushed into cooler waters by the East Australian Current.
The Integrated Marine Observing System said most of the fish appeared to be leatherjackets, although there were also whiting, black sole, pufferfish, boxfish, sea urchins and flathead.