Extinction of smalltooth sawfish

April 7, 2023, 12:57 p.m.

There are five sawfish species worldwide and all are considered critically endangered and poorly studied. The smalltooth sawfish (Pristis pectinata) is an elasmobranch related to skates, rays, and sharks, and is only one of five species of sawfishes. They possess a characteristic long, flattened, toothed rostrum (often referred to as the "saw") and a flattened head and trunk.

The sawlike snout, called a rostrum, can be used in a back-and-forth swiping motion to cut prey in half or to dig through the sediment. Yet its bill makes it especially prone to capture by fishermen's nets, and throughout the twentieth century, people killed the sawfish as a curiosity — a novelty to be stuffed and mounted on a wall.

Sawfish populations are declining due to overharvesting and entanglement in fishing gear, as their long, toothed rostrums become very easily entangled with fishing line and nets. The saws are dried and sold as trinkets in some cultures. Additionally, loss of mangrove forests and other nursery habitats in the Southeast for conversion to beachfront development contributes to the decline of sawfish.

Unmistakably unique, smalltooth sawfish resemble sharks in appearance but are actually large, bottom-dwelling rays.

Sawfish eat fish and crustaceans. The saw is key to catching and killing prey—in addition to its use as a weapon or digging tool, the saw has small pores that can detect electric fields produced by prey. This supersense is common to sharks and rays alike.

Fishing still poses a threat to the smalltooth sawfish. Gillnets entangle the fish, and fishermen sometimes kill sawfish simply to keep their nets from tearing. Once numerous in all North American tropical waters, the species has now been reduced to an estimated 2 percent of its former range and population — now occurring in only a few spots in Florida. The smalltooth sawfish (Pristis pectinata) is the only sawfish species found in Florida waters.

Sawfish are unique and intriguing animals.

The smalltooth sawfish is one of the largest species of sawfish, reaching lengths of up to 7.6 m (25 feet), 25 percent of which is their rostrum or snout, and weights of nearly 300-350 kg (660-770 pounds). Their bodies are flattened with wing-like pectoral fins. They are an olive-brown color on their backs and a whiter underside. These fish have a very distinct snout, which resembles a long, flat saw. Along the edges of its rostrum are teeth-like structures called denticles around the edge and between 10 and 12 rows of teeth in their mouths. True to its name, the smalltooth sawfish has smaller teeth than other species of its family.

Though the rostrum is a vital component of smalltooth sawfish biology and ecology, it is also a large part of the cause of its overwhelming depletion. The rostrum is easily entangled in fishing nets. Coastal net fisheries targeting this or other species drove down the numbers dramatically.

Little is known about what the smalltooth sawfish feeds on. Their diet is thought to consist of crabs, shrimp, small fish, and other bottom-dwelling organisms. The saw is used to slash at prey in the water column and to dislodge prey from bottom-dwelling habitats.

Historical threats have included unintentional overfishing associated with commercial fisheries, trophy fishing associated with recreational fisheries, and habitat destruction. Presently, fishing gear entanglements and habitat destruction are the main threats as the amount of recreational and commercial fishing has increased, and the development along Florida’s coast has caused damage to mangrove forests that serve as nursery areas for juvenile smalltooth sawfish. Recent research has shown that water temperatures below ~53°F (12°C) cause smalltooth sawfish mortalities and this observation suggests that the northern limits of its year-round range may not have extended much further north of Florida.

Smalltooth sawfish use their long rostrums for the dual purposes of locating prey and immobilizing it. The rostrum is covered with special organs that help these fish locate prey in the low visibility of coastal waters by sensing the electric field created by other fishes and invertebrates. After locating small fish prey, smalltooth sawfish shake their heads from side to side, injuring or stunning fish and making them easier to capture. This behavior is analogous to that used by swordfish and thresher sharks. Smalltooth sawfish also use their electric sense and their rostrums to dig for buried invertebrates in soft sediments on the sea floor. Using these methods, smalltooth sawfish eat a variety of prey.

Smalltooth sawfish reproduce via internal fertilization, which results in between 15 and 20 embryos on average. Sawfish are ovoviviparous, meaning females carry developing embryos internally and give birth to live pups. The pups’ saws are fully developed but they do not have denticles to prevent injuries to their mother during birth. Once pups are born, they are independent and do not receive any parental care. They reach reproductive maturity at around 10 years old and can live to be as old as 30 years old.

The smalltooth sawfish’s natural range spans from the waters off North Carolina and throughout the Gulf of Mexico. Today, they are limited to the waters of South Florida. In fact, the Ten Thousand Islands area off the peninsula’s southern tip is one of the only places where the species is common.

As mentioned earlier, sawfish are unique and intriguing animals, and their conservation is extremely important for aquatic ecosystems.

What actions do you think should be taken today in order not only to preserve this endangered species, but also to increase its population?