Sawfish are the ultimate stealth hunters, study finds
The feeding habits of sawfish have long been shrouded in mystery, but new research has revealed the fascinating function of the species’ distinctive saw-like snout.
Sawfish are a type of ray identified by their unique flattened body and snout (rostrum), lined with razor-like teeth.
The species is found in both fresh and saltwater, largely in the remote Kimberley region of Western Australia. Until now there has been limited research into sawfish, meaning its behavioural and feeding habits have not been well understood.
However, in a collaboration between engineers and biologists from the University of Newcastle (UON), Murdoch University and Sharks and Rays Australia, experts have shed new light on the critically endangered species.
For the study – published in The Journal of Fish Biology – researchers used CT technology to create 3D scans of the snouts from three sawfish specimens and then applied a ‘virtual wind tunnel’ to imitate their movement through water in a computer model.
They found that the hydrodynamic shape of the snout results in minimal impact to the surrounding water, allowing sawfish to sneak up on prey undetected. The research also builds on previous findings that sawfish use a rapid lateral swim action to impale their kill.
3D model of a sawfish moving through a ‘virtual wind tunnel’. Image credit: UON
“The hydrodynamic nature of their rostra makes any movement barely detectable in water. 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,” said lead researcher Associate Professor Phil Claussen from UON.
The new findings debunk the previously widely accepted theory that sawfish sift through silt to uncover their food. “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,” Phil explained.
In an interesting twist, the research collaboration was sparked by an episode of the TV show River Monsters. UON engineer Sam Evans had seen a feature on the threatened sawfish and reached out to Murdoch University fish biologist Associate Professor David Morgan who featured on the episode as an expert.
“Our work historically has been in wind turbines, so I am interested in the movement and efficiency of blades – I thought the sawfish rostrum was incredible and would be a really interesting specimen to model,” Sam said.
David said he has seen hunters removing the snouts (rostra) of sawfish to keep “as a kind of trophy”, and hopes that with this new research will drive home the importance of the snout to the species’ survival and discourage “this destructive phenomenon”.
