A shark seen thrashing about in the shallows of an Australian beach and later washed up dead, died because it had a sea lion stuck in its throat.
The death of the tagged great white shark near Geraldton was investigated by the Department of Fisheries.
The shark was filmed by a number of bystanders on a beach in the Mid-West on Saturday, as it swam into the shallows, beaching itself at times and thrashing about a few metres from the shore.
A video of the shark's behaviour was posted on YouTube on July 12 and has since had more than 17,000 views.
The shark was found washed ashore at Coronation Beach, about 28 kilometres north of Geraldton.
Research scientists travelled to Geraldton in an effort to determine what happened to the shark.
Principal research scientist Dr Rory McAuley said the shark had been fitted with an acoustic tag, which had been handed in to the department.
He said the four-metre male shark had no visible signs of injury or disease, however it appeared the shark had a large Australian sea lion stuck inside its throat.
"This could explain why the shark was exhibiting such unusual behaviour in shallow waters off Coronation Beach. It is possible that the shark was trying to dislodge the blockage," McAuley said.
"Such a large object may have damaged the shark's internal organs or impeded water flow into his gills, contributing to his death. Alternatively, the shark may have accidentally become stranded in his attempts to get rid of the obstruction."
The department has also confirmed that the shark was tagged in South Australia in January this year.
"Confirmation of when and where this shark was tagged demonstrates the extraordinarily mobile nature of this species," McAuley said.
Tissue and vertebral samples were taken for future genetic, age and growth, ecological and population assessment studies.
Tash Tapper, who captured the footage of the shark while at the beach with her family on Saturday said it was a surreal experience to see a shark acting so strangely and coming so close to the beach.
She said police were at the beach after being made aware that a shark was in the area, they had earlier warned surfers to get out of the water following a warning from the Fisheries Department of a shark sighting in the area.
Tapper said she watched the shark swim in close to the shore, back out and back in for almost two hours.
She said while initially onlookers tried to assist the shark when it beached itself on a reef, they soon realised the shark was not well and might not be able to be helped.
"To me it seemed it was coming in to die," Tapper said.
The current shark tagging and monitoring programme in WA began in an experimental phase in 2008 with a more dedicated and comprehensive white shark monitoring program established in late 2011.
The programme is designed to record information about shark behaviour in WA and is part of a greater shark mitigation scheme introduced following a spate of fatal shark attacks in the state.
The network monitors more than 300 sharks with external tags, less than half of those are great white sharks, the species identified as being responsible for recent fatal attacks in WA and some also have internal tags.
- WA Today