On second thought, that's not entirely accurate. Comparing a sawfish to a "madman" might give you the impression that these cousins of stingrays are unruly or careless when it comes to dispatching prey with their serrated snouts, when, in actuality, recent evidence suggests the exact opposite to be the case. Truth be told, sawfish are a lot more like chainsaw-toting surgeons.
This observation was made by University of Queensland Biologist Barbara Wueringer, who used chunks of mullet and tuna meat to observe the predatory behavior of juvenile Pristis microdon — one of the seven known species of sawfish. In tomorrow's issue of Current Biology, Wueringer and her colleagues write that the rapid, back-and-forth swiping motion of a hunting sawfish is strong and accurate enough to "split a fish in half, impale it on the rostral teeth, or sweep it [to the sea floor]," where the sawfish could use the blade of its saw to pin its prey in place.
The team's observations provide some of the most compelling evidence to date that sawfish use their snouts actively and deftly as a predatory weapon. But it's also significant for two other reasons.
The first is that it suggests sawfish are an exception to a long-standing rule. Sawfish, like other rays and sharks, can detect electrical fields given off by their prey. This adaptation allows these creatures to seek out food even in dark or murky environments. But according to Wueringer, fishes with elongated rostrums like the sawfish typically use them to either sense prey or manipulate it, but not both.
This video, however, shows that sawfish contradict this rule of mutual exclusivity. You won't find any actual prey in this clip; instead, Wueringer and her colleagues have positioned weak electrical dipoles at and above the ocean floor. Yet, according to the researchers, the swiping motions you see the sharks performing closely resemble those observed during feeding, and only occurred in the vicinity of the dipoles. Last year, Wueringer and her colleagues published the first findings to show that the saws of P. microdon are covered in thousands of electroreceptors — this video provides empirical evidence that these electroceptors are in fact used for active predation.
The second reason is that these findings could play a vital role in saving the sawfish — already classified as critically endangered — from extinction.
"Sawﬁsh are skilled predators but, ironically, the saw is partly to blame for their global decline: the saw is easily entangled in ﬁshing gear, perhaps as a result of targeting prey caught in the net," write the researchers. With any luck, conservationists operating with an improved understanding of how the sawfish hunts and forages will be better equipped for looking after and protecting these striking creatures.
The researchers' findings are published in the latest issue of Current Biology.
Top photo by Andy Murch via; video by Dr. Barbara Dueringer via Current Biology