The sharpened teeth on the saw-like snout of the critically endangered Australian sawfish is proving little defence against its deadliest underwater predators, the crocodile and shark.
A rare photograph released by Murdoch University shows a young sawfish caught in the clutches of a freshwater crocodile's jaw.
It is a common occurrence for the struggling species which is also targeted by bull sharks, researchers said, as young sawfish venture upriver for the first five years their life before returning to the ocean as an adult.
"For a fish that is pupped at around 800 millimetres total length with formidable weaponry, one would assume that rates of natural predation would be low," said the university's lead fisheries researcher David Morgan on Thursday.
"But their upstream migrations are fraught with danger, and we suspect they don't always survive."
Examining 39 sawfish, which can grow up to six metres, in Western Australia's Fitzroy River, researchers found 60% had wounds received from crocodile or bull shark attacks, with their findings published in The Scientific Naturalist
"These scars suggest that freshwater crocodiles attempt to capture and consume sawfish regularly, but are unsuccessful possibly due to the size, sensory capabilities and defences of their prey," Morgan added.
The risk of extinction for the sawfish is heightened by the loss of their natural habitat, getting caught in fishing nets and by hunters seeking a trophy fish.
Researchers are urging a rethink of management techniques for Australia's northern river systems to better protect the vulnerable fish.