Saw-like Snout Is a Multifunctional Hunting Tool

underwater silhouette photograph of a sawfish

Biological Strategy

Smalltooth sawfish

Jeanette Lim

Image: ChameleonsEye / Shutterstock / Some rights reserved

Sense Electricity/Magnetism From the Environment

Some living systems use electric or magnetic signals as a way to receive information from their environment. Magnetic and electric fields can help such living systems determine direction, altitude, or location, and electric fields also help living systems find other living systems. Detecting and interpreting electrical and magnetic signals requires specialized techniques. For example, mud-dwelling bacteria use crystals composed of magnetite to sense geomagnetism, which helps orient the bacteria to burrow deeper into the mud.

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Physically Break Down Living Materials

Living materials are those that are part of living systems (whether currently or formerly alive). For example, a fallen log, although dead, is considered a living material. Breaking down or breaking up living materials is important for living systems that feed on them, as well as in facilitating the decomposition of organic matter. Breakdown increases the material’s surface area exposed to moisture, fungi, bacteria, and other living systems, many of which use enzymes and other chemicals to further break it down. But living materials can be difficult to break down because, for their own survival, their composition must provide support and protection. Therefore, living systems require mechanical means (such as grinding, tearing, or chewing) to manipulate these materials, as well as strong materials that can overcome resistance. For example, small beetles that chew through wood have large, strong jaws that enable them to cut through this tough material.

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Capture, Absorb, or Filter Organisms

Many living systems must secure organisms for food. But just as one living system must capture its prey to survive, its prey must escape to survive. This results in capture and avoidance strategies that include trickery, speed, poisons, constructed traps, and more. For example, a carnivorous plant called the pitcher plant has leaves formed into a tube that collect water. Long, slippery hairs within the tube face downward. When insects enter the tube seeking nectar, they lose their footing and slide inside, unable to climb out and escape being eaten and digested by the plant.

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Fish

Class Agnatha (“without jaws”), Class Chondrichthyes (“cartilage fish”), Superclass Osteichthyes (“bone fish”): Sharks, eels, snapper, hagfish

The fish are a diverse group, comprising multiple classes within Phylum Animalia. The most well-known classes are Chondrichthyes, which has sharks and rays, and superclass Osteichthyes, which has all bony fish like cod and tuna. Unlike other vertebrates, fish only live in water. They use special adaptations like fins, gills, and swim bladders to survive. Most are ectothermic, meaning their body temperature depends on the water temperature around them. Over half of all vertebrates are fish. They’re found from the bottom of the sea to high mountain lakes.

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The saw-like snout of the sawfish is a multifunctional hunting tool that both senses and handles prey.

Sawfishes are active predators with a fearsome appearance to match. These relatives of sharks and rays are famous for their “saws,” long flattened snouts that bear spiky teeth-like projections on either side, giving the sawfish its name. The saw functions mainly as a multifunctional hunting and feeding tool: it can both sense and handle prey in the water column or near the bottom. This makes the sawfish’s saw unique, as elongated snouts in other fishes are known to either sense or handle prey, but not both.

Like sharks and rays, sawfishes use electrosensitive receptor cells in their skin to sense electric fields that are produced by all living organisms. This sensory ability can be especially helpful when hunting in murky or dimly lit waters. Electroreceptor cells are particularly numerous on the top and bottom of the sawfish’s saw. The sawfish can search for nearby live prey sitting atop or partially buried in sand by waving its saw above the substrate, much like a handheld metal detector. Once a prey item is found, the sawfish can use its saw to pin the prey down or reposition it before biting into it. The saw can also detect live prey in the water column. Once prey is encountered there, the sawfish thrashes its saw side to side, resulting in prey that’s knocked out, cut apart, or impaled.

Sawfishes live in freshwater and marine inshore waters, where they are critically endangered worldwide. For instance, numbers of smalltooth sawfish (Pristis pectinata) off the coast of Florida have dropped significantly due to declining estuary health and overfishing.

For a video of the sawfish’s saw in action, check out this ScienceShots article.

Image: Sandra Raredon/Smithsonian Institution / Public Domain - No restrictions

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Image: D Ross Robertson / Public Domain - No restrictions

Last Updated June 28, 2017

References

“…[J]uvenile freshwater sawfish Pristis microdon [now known as Pristis pristis] are active predators that use their toothed rostrum — the saw — to both sense prey-simulating electric fields and capture prey. Prey encountered in the water column is attacked with lateral swipes of the saw that can stun and/or impale it.” (Wueringer et al. 2012:R150)

Journal article

The function of the sawfish’s saw

Current Biology | 01/01/2012 | Wueringer BE; Squire L; Kajiura SM; Hart NS; Collin SP

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Reference

Journal article

The biology of extinct and extant sawfish (Batoidea: Sclerorhynchidae and Pristidae)

Reviews in Fish Biology and Fisheries | 01/01/2009 | Wueringer BE; Squire L; Collin SP

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Reference

Journal article

On the Utility of the Saw of the Sawfish

Copeia | 01/01/1952 | Breder CM

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