Australasian Science: Australia's authority on science since 1938

Sawfish Revealed as the Ultimate Stealth Hunter

Researchers from The University of Newcastle have solved a long-standing mystery surrounding the stealth-feeding behaviour of the critically endangered sawfish.

Sawfish are a type of ray found in both salt and fresh water in the Kimberley region of Western Australia. They have a flattened body and a rostrum (snout) lined with razor-like teeth.

Due to their rarity and preference to feed in murky water, sawfish feeding habits have seldom been sighted in the wild. Until now it was widely believed that sawfish sift through silt to uncover their food. The new research, published in The Journal of Fish Biology, described how sawfish detect prey with their rostrum and then swipe rapidly from side to side to impale their kill.

Utilising CT technology, rostra specimens of three sawfish species were scanned to create 3D models. A virtual wind tunnel was then used to imitate their movement in water, revealing that the rostrum’s hydrodynamic shape causes minimal disturbance to the surrounding water.

“The hydrodynamic nature of their rostra makes any movement barely detectable in water,” said lead investigator A/Prof Phil Clausen. “We were surprised at how fast the motion was – our modelling clearly shows that with a lateral swipe, by the time the sword reaches the prey, it’s already too late.

“Our work also shows moving the rostrum a few centimetres above the ground creates almost no disturbance at all, which would make stirring the river or sea bed difficult,” he said.

Co-author and Director of Sharks and Rays Australia, Dr Barbara Wueringer, explained that “the shape of the rostrum is likely to reduce noise in the water, increasing the ability of sawfishes to detect minute vibrations caused by prey during their lateral swipes. The results of our work will help us with a better understanding of their habits and ultimately help us improve our conservation efforts,” she said.

Co-author A/Prof David Morgan from the Centre for Fish and Fisheries Research at Murdoch University has tagged hundreds of sawfish in the Fitzroy River, and worked closely with indigenous ranger groups in the area. “We have encountered instances of hunters removing the rostra as a kind of trophy,” he said. “The findings of our study show just how instrumental sawfish rostra are for their survival, and we would urge the few remaining human population centres that have sawfishes inhabiting their local waters to address this destructive phenomenon.”