Search and Destroy: Sawfish are handier with their blades than previously thought

With their long, serrated snouts, the sawfish might strike you as a little like aquatic versions of Leatherface. Scientists used to think the two were behaviorally comparable: sluggish and maybe a little dimwitted, just waving their saw around blindly and waiting for something to run into it. New research by Barbara Wueringer and colleagues from Australia and the US, though, shows that the fish actually wield their saws with considerable skill. They’ve also learned that the sawfish’s nose knows, too, and is a complex sensor as well as a weapon.

The sawfish family has not been heavily studied (a shame considering that all seven species are endangered), and with only a few firsthand accounts of how the fish hunt, researchers could only speculate on how the saws were used. One of the more common suggestions was that they were bottom feeders and raked their snout through the sand to snag buried prey on the saw’s teeth. Other ideas were that the fish cut into the sides of whales or slashed their way through schools of fish.

To figure out what was really going on, Wueringer and her team captured young freshwater sawfish in northern Australia and watched them feed on mullet and pieces of tuna. The fish went after the food in two different ways, depending on whether it was floating in the water or lying at the bottom of the tank. In the water, they quickly slashed at the prey to impale it on their saws’ teeth or knock it to the bottom or into position to eat. Some of these strikes were strong enough to cleave the fish in half. At the bottom of the tank, the sawfish used the underside of their saws to pin prey down and then move them into position to ingest, and usually preferred to eat the mullet headfirst. This video shows all of these maneuvers.

The sawfish weren’t just spearing wildly, either, and the study found that their snouts are part lance and part smart missile, with buit-in tracking systems. Sawfish are closely related to rays, skates and sharks, and share their sensitivity to electrical fields and their ability to use them to navigate and detect other animals.  Wueringer discovered a few years ago that sawfishes’ saws are covered in electroreceptors, and when she presented the sawfish in this new study with electrodes that mimicked the electric signals prey would give off, the fish reacted the same way they did to the food.

The sawfish’s saw has turned out to be more impressive than anyone thought, but cause the fish a lot of trouble, too. Every sawfish species is listed as Critically Endangered by the IUCN Red List, in part because their saws are prized by shamans in Asia as tools for expelling demons and disease, and are easily caught on fishing hooks and lines.

Reference: Barbara E. Wueringer, Lyle Squire, Stephen M. Kajiura, Nathan S. Hart, & Shaun P. Collin (2012). The function of the sawfish’s saw
Current Biology, 22 (5), 150-151 : 10.1016/j.cub.2012.01.055

Image: “What a saw” by Lorenzo Blangiardi. Used under a Creative Commons license


3 Comments, Comment or Ping

  1. Sherryl Walkingshaw

    Is the Saw Fish and Sword Shark the same???

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