Residents discovered the dead shark underneath a jetty on Riverton Drive North, near Zenith Street.
The shark appeared to have been caught by a fisherman, filleted and the carcass dumped on the beach.
Swan River Trust principal scientist Kerry Trayler said it was extremely rare for a shark to appear on Swan and Canning river foreshores.
‘I’ve been working for this organisation for eight years and we’ve never seen one,’ Dr Trayler said.
‘We don’t know what’s happened to this shark. There’s all sort of factors that could have impacted it.’
Dr Trayler said bull sharks were a common species in the river but very little was known about their movements.
‘During the season when the sharks are most active in the river, which is in the summer to early spring, we get the occasional sighting but these often aren’t confirmed in any way,’ she said.
‘What we believe happens with bull sharks is, they come into the river system from November to January and they go up river to pup, produce live young, and then the females will mate again and go back out into the ocean.
‘We don’t think they stay in the river system, although they can live in freshwater river systems.’
Dr Trayler said that because of the shark’s size it was likely to be a juvenile and river fishermen usually caught sharks about 2.5m in length.
Canning River Canoe Club secretary Christian Thompson said in his 20 years living in Shelley he had never seen a shark but dolphins were frequently sighted in the Canning River.
‘There are urban myths that people see sharks and some of us occasionally say they thought they saw something like a shark,’ Mr Thompson said.