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Consider: the Largetooth Sawfish

Updated: Jul 2, 2023

Happy New Year everyone! Before I jump into things this month, I want to thank all of the amazing artists who submitted to the 2022 Consider Art competition. The quality of artwork is way above anything I would have expected, and I think the other judges and I are going to have a lot of fun choosing a winner! Results of the competition will be posted soon, so stay tuned.

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In case you haven’t noticed by this point, I really like animals with weird noses. From the long, skinny snout of the olm to the purple frog’s stubby sniffer, weird noses often make otherwise normal-looking animals stick out. A funky nose can make an animal’s face not fit into pre-existing categories that we have filed other animals into. Noses can also be modified to serve many different functions. A pig’s nose, for example, is reinforced with cartilage to function as a highly-effective digging tool, while the wide, flat snout of a hammerhead shark helps to give the animal both excellent electroreceptive abilities and a near 360-degree range of vision. We have already seen how the olm’s snout helps it to navigate its surroundings without any eyes and the purple frog’s nose helps it to make it look more like a whoopee cushion filled with Jello.

But out of all of the strange noses we have talked about here, none of them can do quite what today’s creature can. Sure, many animals have noses with excellent sensory reception or modifications to provide increased utility, but unlike today’s creature, very few animals have modified their noses to be lethal weapons. Consider: the Largetooth Sawfish, Pristis pristis.

A Largetooth Sawfish swimming in an aquarium, the full glory of its absurdity on display.
Image Attribution: FSamuels from Flickr under CC BY-SA 2.0.

Kickass, right? Imagine seeing one of these suckers at Home Depot. Largetooth sawfish are the second-largest of the five species of sawfish found around the world. They are ray-finned fishes, meaning that they have a cartilaginous skeleton and splayed pectoral fins which attach to their heads. While they may look like sharks, sawfish are more closely related to guitarfish and rays. Largetooth sawfish get very big, up to 6 meters (~20 feet), and can weigh 500-600 kilograms (1100 to 1300 pounds, or roughly as much as 2700 Big Macs for my American readers). Despite being so big, largetooth sawfish grow quite slowly, and only reach sexual maturity by age ten. They live up to thirty years.

But that nose though! Well, scientifically the massive schnozz of a largetooth sawfish is referred to as a “rostrum”, not a nose, but it still possesses useful sensory abilities. Largetooth sawfish rostra can grow to be a quarter of the animals’ body length (1.5 meters or 5 feet). The rostrum is lined with teeth—yes, those spikes are teeth—which over millions of years of evolution decided that sitting in nice neat little rows inside of a mouth just wasn’t hardcore enough for them. In addition to making them look like a scuba diving lumberjack's wet dream, sawfish rostra are highly effective hunting tools. The kinds of small fish that sawfish like to eat often keep to tightly-packed schools which move through the water almost like a single massive organism. With the closely-packed fish all moving at the same time, it becomes very difficult for a predator to tell where one fish ends and another begins. Incidentally, this same strategy is used by zebras on land, and is one of the reasons why zebras have stripes. A weapon like a sawfish’s rostrum, though, can sweep through the schooling fish without needing to target a single individual, allowing the largetooth sawfish to hunt schooling fish quite efficiently. When going after bottom-dwelling creatures like crabs or worms, the rostrum can be used to dig up and pin down buried prey, preventing them from escaping. Despite being a useful weapon, largetooth sawfish have to be careful with the teeth along their rostra, as if the teeth are damaged or knocked out, they will not regrow.

As top predators, largetooth sawfish perform a valuable ecological duty in their habitats. Many of the prey items sawfish catch are sick or injured animals, which have the potential to spread diseases to others of their kind if not killed. This is generally true of top carnivores; healthy animals are more capable of escaping predation. Additionally, sawfish tend to dig up a lot of mud and sediment when they capture prey on the seafloor. This digging process can help to flush out other bottom-dwelling animals, such as crustaceans and worms, making them easier targets for other predators.

The largetooth sawfish’s rostrum has another extremely impressive ability, one it shares with its evolutionary cousins, the sharks and rays—electroreception. Largetooth sawfish rostra are dotted with sensors known as Ampullae of Lorenzini, extremely small cylinder-shaped organs built into their skin. These cylinders contain a gelatinous substance which is highly-conductive to electricity, allowing largetooth sawfish to pick up on electrical impulses in the water. Animals release electrical impulses any time that they move their muscles, and cartilaginous fish like sawfish, rays, and sharks can use this to sense nearby prey, even when that prey is buried under mud or camouflaged. Thanks to this ability, the largetooth sawfish can use its rostrum like one of those handheld metal detectors TSA agents try to harass you with, sweeping it across the ocean floor to find buried crustaceans, fish, and worms.

The sawfish’s rostrum is so useful that it is actually not the only type of cartilaginous fish that has one. Their distant cousins, the sawsharks, also have long rostra covered in teeth that they use in much the same way. Despite their similarities, though, sawsharks and sawfish actually aren’t that related. Sawfish are in the evolutionary order Selachimorpha, which contains all modern sharks, while the sawfish are in a completely different order, Rhinopristiformes. Translated from Nerd-ish, that means that a sawshark is more closely related to a great white or a hammerhead than it is a sawfish, even though the two species look very similar. The process by which two animals both evolve similar features without being closely related to each other is called Convergent Evolution. Think of how a shark and dolphin have very similar fin positions and swimming styles, despite being completely unrelated, or the wings of birds versus those of bats. Sometimes, a particular adaptation is so handy that multiple groups of creatures evolve the same structures just by happenstance, and such is the case with the saw-nosed cartilaginous fish.

You can tell the difference between a sawfish (left) and sawshark (right) in a few ways. Firstly, you can ask the animal very politely. If that does not work, you can look at the length of the teeth along the animal’s rostrum. A sawfish’s teeth are evenly-spaced and uniform in length, while a sawshark’s teeth are of multiple different lengths. A sawshark additionally has its gills on the sides of its body behind its eyes, like most fish, while a sawfish’s gills are located under its body, like a ray’s. Some sawsharks also have barbells along their rostra, while sawfish never have this. Image attributions: Left: Flavia Brandi, under CC BY-SA 2.0. Right: Simon Weigmann et al., under CC BY-SA 4.0.

Now for the part you’ve all been waiting for—how do these things bone? Like all sharks and rays, male largetooth sawfish have claspers, a set of sexual organs attached to their pelvic fins which act like a penis. So yes—sharks and rays have two penises. The next time you hear some snub-nosed teenager bragging about how well-endowed he is, you can kindly remind him that no matter how big his hog, he has half the dick that a sawfish does. Largetooth sawfish mating occurs in the summer, with females being able to give birth once every two years. Exactly how largetooth sawfish choose a mate is currently unknown (personally, I really hope that their mate selection process involves Highlander-esque sword fighting, but I have found no evidence of this actually occurring).

Gestation takes around five months, and the sawfish pups are born live. Largetooth sawfish babies exhibit a process known as “yolk-sac viviparity”, meaning that they develop within an egg sac inside of their mother, feeding on the nutritious yolk while they develop. A mother can give birth to up to 13 pups at a time, and these pups are BIG: 76-90 cm (2.5 to 3 feet long) right out of the womb. When born, the teeth of the sawfish pups’ rostra are covered with skin like a sheath so that they don’t rip up their mothers on the way out. The teeth erupt out of the sheath shortly after birth. Largetooth sawfish pups usually inhabit freshwater ecosystems such as rivers, then swim out to sea as adults. Rivers tend to have smaller species compared to the open ocean, so they act like peaceful nurseries for sawfish babies to terrorize. Like almost all ray-finned fishes, sawfish do not care for their young, releasing them into a river delta with a pat on the back and a “good luck, kiddo”.

Largetooth sawfish were once widespread across tropical environments around the world, but their range has been significantly reduced. Once upon a time, largetooth sawfish could be found all along the coasts of the tropical regions of the Americas, Africa, India, and Australia. Nowadays, however, their remaining populations can be found in Nicaragua, India, Bangladesh, the coastal areas of the Amazon, and Northern Australia, where their populations are highest. While largetooth sawfish have been seen in the Gulf of Mexico and Florida in the past, they haven’t been spotted there in over fifty years, so they are probably extinct in the region (guess they don’t like freedom…or, you know, oil spills). They primarily inhabit coastal mangrove forests, as well as mud flats and estuaries (places where rivers flow into the sea). Largetooth sawfish are capable of surviving in both fresh and saltwater environments, a rare ability amongst fish, and can even be found within enclosed freshwater habitats like Lake Nicaragua.

Largetooth sawfish being harvested by fishermen in Florida, 1950. Sawfish have been hunted for their teeth, fins, rostra, and skin for millennia, with evidence going back to ancient Mayan cultures in the Yucatan Peninsula. Image Attribution: Florida Department of Commerce, Public Domain.

In short, humans have beaten sawfish populations around the world to a pulp. Every species of sawfish is classified as Endangered or worse by the International Union for the Conservation of Nature (IUCN), and the largetooth sawfish is considered by many conservationists to be the single most endangered species of all cartilaginous fish. Largetooth sawfish struggle due to a variety of factors, but two that stick out are harvesting for resources and fishery bycatch. At least five different parts of the largetooth sawfish are traded, from their long rostra, which some people collect as exotic curios, to their skin, which has been used to make boots since the 19th century at least. Sawfish teeth have uses in traditional medicines around the world, and like many cartilaginous fish, their fins are harvested for soups. Humans have harvested sawfish parts for thousands of years. Their teeth have been found in the graves of ancient Mayan people, and there is evidence of Yucatan cultures using sawfish rostra as ceremonial weapons (which I will admit is extremely badass despite the consequences for the species).

Even bigger than intentional harvesting, though, is bycatch in the fishing industry. Bycatch occurs when a fish or other marine animal is unintentionally caught in a process designed to catch some other species. Many net-fishing techniques, such as trawling, have an extremely high bycatch rate, which has impacted the populations of tons of species, from dolphins to sea turtles to our poor largetooth sawfish. It doesn’t help that largetooth sawfish rostra are basically the perfect tools for getting tangled in fishing equipment—they’re long, inflexible, and covered with sharp teeth that can easily catch onto lines and get horribly tangled. Often, rod and reel fishermen will find largetooth sawfish hopelessly entangled in their lines and have absolutely no idea how to free the creature. Other times, fishermen will intentionally kill bycaught largetooth sawfish to prevent them from getting caught in lines again and possibly destroying the fisherman’s equipment.

Human activity also endangers the largetooth sawfish by modifying the habitats they need in order to survive. Because largetooth sawfish pups have to live in freshwater, altering the flow of rivers can have a terrible effect on their populations. When rivers are dammed or their flow is otherwise changed, largetooth sawfish pups become unable to reach the areas that they need to survive and often quickly succumb to marine predators. In other cases, mining has disrupted the coastal habitats the largetooth sawfish live in, driving them from their preferred hunting grounds. Even in the oceans, human activity has managed to destroy the habitats of a variety of species, sawfish included.

Governments and conservationists around the world are utilizing various strategies to protect largetooth sawfish and try to stave off their extinction. The species is protected under the Convention on International Trade of Endangered Species (CITES) treaty, preventing the trade of sawfish parts across national borders. CITES protects many endangered species around the world, such as elephants and rhinoceroses, but many people still hunt CITES-protected animals illegally, the largetooth sawfish included. In coastal northern Australia, the biggest remaining stronghold of largetooth sawfish, gillnet fishing has been largely banned, and the species is heavily-protected by the Australian government. To help protect largetooth sawfish from bycatch, Australia has implemented a training program to teach fishermen how to safely disentangle largetooth sawfish from their lines. This doesn’t stop fishermen from intentionally killing the fish, but it does reduce the likelihood that a fisherman will accidentally kill a sawfish in the process of fishing for a different species. A similar project is underway in Bangladesh under the direction of the Zoological Society of London (ZSL). Here, the ZSL hopes to educate indigenous fishermen on how to identify and release bycaught largetooth sawfish, and many fishermen in the area have been willing to do what it takes to protect the species.

Largetooth sawfish are incredible creatures, ruthless hunters who take the phrase “follow your nose” to the extreme. Despite looking ridiculous, they were highly successful hunters before humans began to encroach upon their territories, and their bizarre chainsaw-face is such a useful adaptation that other fish species have convergently evolved it. Sawfish are important to the ecosystems they survive in, culling sick animals and flushing out buried organisms for other carnivores to consume. If we humans pressure the fishing industry to end these irresponsible high-bycatch methods and develop more protected areas for sawfish, we can ultimately end up with a healthier ocean and a more stable planet.

If you want to help protect the Largetooth Sawfish, consider donating to the Zoological Society of London's EDGE of Existence Program, which seeks to protect evolutionarily-diverse and globally-endangered animals worldwide, the sawfish included. Find out more here.

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