In cartoons, a sawfish could find itself being unwittingly plucked from the water to serve as a handy tool for any number of purposes. In reality, the long, sharp-toothed snouts of these shark relatives are found to be something much more than an appendage reminiscent of a handsaw. Current research shows that, while the sawfish does use its snout to attack, capture, and dismantle prey, the snout also contains advanced electronic sensors that actually help the sawfish locate prey in the first place. Far more than a brutal hunter, therefore, the sawfish is now coming to be seen as something of a psychic stalker that uses a sixth sense to locate its meals.
Sawfishes, also called carpenter sharks, are a family of rays characterized by a long, flattened nose known as a rostrum. Sawfish can reach lengths of over 5 meters, and have rostrums of a meter or more. The rostrum is lined with transverse teeth that give it its resemblance to a saw. But perhaps not so recognizable with the casual glance is that the rostrum also contains tiny pores, or electroreceptors, which allows the sawfish to sense the movements of small electrical fields emitted by passing prey. Basically, its an antenna with teeth. But for all their fierceness and special talents under the water, sawfish are currently recognized as an endangered species. Scientists hope that this deeper understanding of sawfishs special sense will help researchers to be better able to protect them.
This is indeed one hope of marine biologist Barbara Wueringer of the University of Queensland. “We know so little about sawfish, even though these animals can grow really big,” she said in a conversation about her research. “To know that the saw acts like an antenna that can sense prey is amazing.”
But, in order to better understand exactly how the sawfishs special sense assists it in capturing prey, Dr. Wueringer needed to see it in action; she had to see the sawfish hunting, responding to the electrical fields being emitted by its potential prey. Australian ethical standards regarding animal study, however, prohibit researchers from watching animals hunt live prey. The solution was to dangle pieces of mullet and tuna into a tank of sawfish while also creating in the tank the weak electrical signatures characteristic of these animals. The results were caught on film.
The films show sawfish aggressively stalking prey and swiping at it with their rostrums. Some blows were so powerful that sometimes the chunks of dead fish would be split in two. They also use their rostra to pin fish to the bottom. What they were not seen to do, however, was use their rostra to poke around through the sediment looking for food, although they would use sediment to sharpen their teeth. This behavior suggests that the sawfish are far more aggressive hunters than previously thought.
Dr. Wueringer also mapped the locations of the sensory pores on the sawfishs rostrum. She found that the pores were concentrated on the upper portions of the sawfish’s teeth, the perfect location for the sawfish to both see and stalk prey.
Sawfish are currently recognized as an endangered species. They have been threatened both by overfishing–their rostra being an especially cherished trophy–and by being unintentionally caught in commercial fishing nets–their sharp teeth easily leads to entanglement. Like their relatives the sharks and rays, sawfishs slow growth and reproduction make them particularly vulnerable to any increased threat. Having a better understanding of how they hunt–how aggressive they are and how they sense prey–offers several ways to help address the threats to them.
These methods could be both high tech and low tech. For example, knowing that the sawfish are attracted to the electrical fields of their potential prey, those in the fishing industry could use magnetic or electrical fields to keep the sawfish away from fishing nets. Also, because it simply wasn’t known that sawfish were as aggressive a hunter as they actually are, fishing could be limited in areas where sawfish populations are particularly large, to prevent potential conflicts.
While BioZine is on summer vacation, we hope you enjoy this article from the archives. This article was first published in March 2013.