IT WAS an afternoon in January, during a break in the weather, when a Florida State University research vessel headed out towards the Queen of Nassau shipwreck off the Keys. There had been sightings of smalltooth sawfishes in the area and ecologist Dean Grubbs was keen to investigate. Resembling a chainsaw with a shark-like body, sawfishes are extremely rare. With luck, Grubbs might catch one or two for tagging and study. It never occurred to him that he would soon have six snagged on a single line. That was when things started to get tricky.
Adult sawfishes can be more than 4 metres long and weigh over 300 kilograms, which meant reeling them in wasn’t an option. The animals needed rescuing, and fast. So Grubbs jumped in. Holding his breath 6 metres underwater, he began to lasso their toothy snouts while trying to avoid being slashed to bits. “[It] was a little nerve-racking,” he says.
Video: Rare chainsaw shark gets tagged by hand
Grubbs’s heroic response was not misplaced. Sawfishes are the world’s most imperilled marine fishes; over the past half century, smalltooth numbers have declined by at least 95 per cent, and the four other species are faring little better. They are also among the strangest of animals, their weirdness extending far beyond their looks. Until recently, we knew little about their unusual habits. But with numbers plummeting, there’s a growing urgency to discover more so that we can try to work out if, and how, these extraordinary creatures can be saved.
Advertisement
Sawfish populations have plummeted in the past 50 years (Image: Kevin Moloney/The New York Times/Redux/Eyevine)
Sawfishes are distant relatives of sharks, more closely related to rays. Once common across tropical and subtropical waters, all five species are now on the International Union for Conservation of Nature’s Red List of Threatened Species. Narrow and dwarf sawfish are classed as endangered; green, largetooth and smalltooth as critically endangered. As well as being dangerous to handle, they spend most of their lives in muddy coastal waters, making them very difficult to study. As a consequence, much about these animals is as murky as the waters they inhabit.
Take the hallmark snout, or rostrum. It has between 18 and 37 pairs of teeth, depending on the species, but until a few years ago, its function was uncertain. Now we know that . They slash their snouts around on the muddy bottom of shallow waters, using specialised organs in them to detect tiny electrical signals generated by small schooling fish, shrimps, crabs and any other animals present. “The saw essentially gives them a very big antenna,” says Colin Simpfendorfer at James Cook University in Townsville, Australia. Electric sensing serves them well in low visibility, he adds, and once they have located their quarry, the rostrum becomes a club to stun and lacerate prey before they “hoover it up”.
“Sawfishes use their hallmark snout, or rostrum, for both sensing prey and rendering their prey insensible”
Grubbs is trying to fill another gap in our knowledge of sawfishes. Within living memory, the smalltooth could be found along a wide swathe of the eastern coastline of North and South America as well as off Africa’s west coast. Now, it is largely restricted to south-west Florida and the Bahamas. It was listed as endangered under the US Endangered Species Act in 2003 on the assumption that the US population is distinct. “But we don’t really know if that is true,” says Grubbs. To find out, he and his colleagues are working in Florida and the Bahamas to track sawfishes and discover whether the two populations intermingle.
That means tagging adults – perilous work, even when you don’t have to dive in to rescue them. “I tell everybody that sawfishes require more respect and are potentially more dangerous than any of the sharks we deal with,” says Grubbs, who handles some 3000 sharks a year. The main threat comes from their rostra, which they swing around like swords when captured. “The angular momentum on the end of the rostrum is unbelievable,” says Grubbs. “And the teeth, especially on the large ones, are very, very sharp.”
Trying to tag sawfish in Florida without getting slashed (Image: Dean Grubbs)
To minimise the handling risks, the researchers typically secure the fish by tying one rope around its rostrum, another around its tail and perhaps a third on its mid-section. They then take its measurements and attach . The tag collects information on depth, light levels and temperature, and is programmed to come away after 45 to 180 days, when it floats to the surface and sends its data to a satellite.
The project began in 2001 and Grubbs’ team is allowed to tag just 20 animals a year. So far the indications are that Floridian sawfishes are not long-haul travellers, preferring to stick close to home. The researchers are also taking small tissue samples for genetic analysis to confirm whether the US population is truly distinct from the Bahamians. “It could only take one or two sawfish [interbreeding] every generation to keep the two populations mixed,” says Grubbs.
As with all small, isolated populations, Floridian sawfishes are in danger of becoming inbred, but other research suggests despite the crash in numbers. Other sawfish species may not have fared so well. Working mostly off the coast of northern Australia, Simpfendorfer and his team are trying to discover whether the narrow sawfish has experienced a genetic bottleneck. Studying sawfishes here is particularly tough because researchers must be constantly vigilant not just for swinging sawfish rostra, but also for saltwater crocodiles. However, these waters are a magnet for research because they are the strongholds of four of the five sawfish species (see “On the slide”).
One thing everyone is keen to find out more about is the sawfish’s highly unusual way of reproducing. Unlike most fish, it goes for internal fertilisation. Maturing males develop pelvic fin extensions called claspers that they insert into the female during copulation. The embryos develop inside the mother’s body without a placenta, feeding only on the yolk of their egg. After a gestation period of 4 to 6 months, the mother gives birth to several offspring – around a dozen is common, but the smalltooth can have up to 20. It sounds like a tall order. “Obviously, if you’ve got a rostrum with these little pointy teeth on it when they’re being born, that would be a problem for mum,” says Simpfendorfer. But evolution has provided an elegant solution: a protective gelatinous sheath for the saw that dissolves away a few days after birth.
Producing young in this way poses another problem, however. The newborns are 60 to 90 centimetres long, depending on the species, making them vulnerable to being caught in fishing nets. Here again, we don’t yet know enough about sawfishes to assess the scale of the problem. What we need to find out, in particular, is when females become sexually mature and how often they conceive, so as to judge their ability to rebound from population crashes.
Unknown quantities
To get a window on these matters, the researchers take a blood sample from each female they catch, measuring levels of the hormones estradiol and progesterone to discover whether she is reproductively mature, has developing eggs or is pregnant. The findings so far indicate that female narrow sawfishes develop fastest, reaching sexual maturity at 3 years old. Female green, smalltooth and largetooth sawfishes all mature at around age 9, give or take a few years. For dwarf sawfish we still don’t know. How often they conceive is even more of a mystery, although the hormone tests may reveal the answer in the future.
Even the lifespan of these fish is uncertain. What we know suggests the narrow sawfish lives for just 9 years, dwarfs and smalltooths may reach their 30s, largetooths their mid-40s and green sawfishes can live beyond half a century. More precise knowledge of fecundity and lifespan will help conservationists work out how quickly a sawfish population could grow if protected. As relatively long-lived and slow-reproducing fishes, they may take a long time to recover.
Lake Nicaragua was once a thriving fishery for these strange creatures (Image: Luis Marden/NGS/Alamy)
“Sawfish are an example of species that slipped through the cracks,” says John Carlson at the US Southeast Fisheries Science Center in Panama City, Florida. “[Populations] have been fragmented all over the globe.” Historically, sawfishes were caught for eating, with their rostra sold as curios, and although they now enjoy some legal protection across most of their range, . Their snaggle-prone snouts make them vulnerable to being accidentally caught in trawl and gill nets. The habitats they rely on, such as mangroves and seagrasses, are being degraded as coastal zones become ever more developed. And some are poached.
The fins are highly prized for shark fin soup, and in China, Indonesia, Australia, Bangladesh and Madagascar. Rostra are still sold as curios and powdered for folk medicines, including a tea taken for asthma. They are even available on eBay, with buyers and sellers in the US, UK, Australia, Germany and Belgium. In Ecuador and Peru, sawfish teeth fashioned into spurs for cockfighting sell for as much as $220 a pair.
“Rostra are sold as curios on eBay and teeth fashioned into spurs for cockfighting sell for as much as $220 a pair”
In the US, the biggest killer is shrimp trawling. With the pop-up tags, Grubbs and his colleagues are getting a better understanding of the locations of critical habitats at various stages in the sawfishes’ life cycle. Their findings could some day make it possible to pinpoint the best times and places to temporarily close fisheries so as to promote sawfish recovery with minimum commercial disruption. For now, the aim is to teach fishers to safely release any sawfishes caught accidentally, since they can survive if quickly freed. and for commercial and recreational fishers.
Saving sawfishes is going to require a concerted effort, despite their cultural significance (see “A fish to fetishise“). In the US, the public is encouraged to report sightings to the , hosted by the Florida Museum of Natural History in Gainesville. But mustering support for conservation remains a challenge, especially in developing countries. Even when caught unintentionally, sawfishes are often retained because their fins and rostra fetch such a good price. Financial incentives to exploit these fishes won’t go away no matter how well fisheries are managed, says Simpfendorfer. “We need to find ways to incentivise conservation… so that we can break that cycle.” Just like handling these magnificent beasts, saving them will be no easy task.
Read more: “6 fish with funny faces – and why they look so weird“
A fish to fetishise
Matthew McDavitt is not your typical cultural anthropologist. For a start, he has a day job as a lawyer. But when he’s not navigating legalese in Charlottesville, Virginia, he is often found fossicking for evidence of human interactions with sawfish. It’s “just a hobby”, he insists, although he has been dabbling in it almost daily for 20 years.
McDavitt’s interest began in childhood, when he was drawn to the sawfishes’ toothy snouts or rostra, but an undergraduate comparative religion course at the University of Virginia really ignited the spark. Exploring the last surviving divinatory almanacs of the Aztecs, “I kept seeing what I thought were sawfish snouts,” he says – symbols that researchers of Aztec iconography had oddly missed. Digging deeper, he discovered that archaeologists had found dozens of sawfish rostra interred beneath the main Aztec temple in Mexico City.
McDavitt had uncovered a lacuna in our cultural knowledge of sawfishes and decided to fill it. He has since travelled the world looking for sawfish art and cultural symbolism, documenting artefacts from West Africa, South America, Indonesia and elsewhere. On Groote Eylandt in northern Australia, he found an aboriginal group for whom the sawfish is an emblem. “You see it on both their civic crests and traditional art all the time,” says McDavitt. “It’s as prominent to them as the bald eagle is to America.”
Other stories have come from trawling the archives. In one account dating back two centuries, a traveller to Lake Maracaibo, Venezuela, describes baby sawfishes so plentiful it was difficult to walk in the shallows without stepping on them. Sawfishes have now been absent there for 150 years. More documents revealed a thriving sawfish fishery in Lake Nicaragua in the 1970s, as well as flesh and fins sold locally and in Chicago restaurants and supermarkets.
Art and folklore are now often the only reminders of how widespread and plentiful sawfishes once were. Depictions of these mysterious, revered creatures are found on ancient jewellery, tapestries, paintings and even on 5000-year-old clay seals found in Iran. In Gambia and Senegal, they were numerous in the 1970s, but are now rarely seen. , reported Ruth Leeney of Benguela Research and Training in Namibia. These days, people in West Africa are more likely to know sawfishes from images on bank notes than as living creatures.
This article appeared in print under the headline “Half shark, half chainsaw”
