“THEY are the most threatened group of organisms on the planet,” says biologist Ivan Jarić. “More than 70 per cent of species are critically endangered, some are almost gone.”
He isn’t talking about the usual suspects: great whales, great apes or the corals of the Great Barrier Reef. He is talking about great fish. Specifically, sturgeons and paddlefish. Together they span 27 species, but 17 are in the most precarious category on the red list of endangered species.
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Actually, make that 26 species. Earlier this year, a team including Jarić that one of the greatest of them all, the giant Chinese paddlefish, is almost certainly no more. It hasn’t been seen in the Yangtze river basin since 2003 and a recent exhaustive search failed to find any. “The chance it still exists is very, very low,” says Jarić, who is at the Czech Academy of Sciences Institute of Hydrobiology.
Sturgeons are the hardest hit of a group of animals that rarely make the headlines, even in conservation biology circles, but this group is declining faster than any other. They are collectively known as “freshwater megafauna” – monster fish such as sturgeons, giant catfish, river sharks and rays, along with river dolphins, porpoises, seals, manatees, crocodiles, alligators, snakes, turtles and salamanders.
“The river megafauna are hidden below the surface of human perception”
All told, there are more than 200 species of freshwater megafauna; most are in deep water and some are probably already doomed to extinction. Yet they are largely overlooked by efforts to save the world’s biodiversity. “It really is a neglected area,” says Sonja Jähnig a the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin, Germany.
The Chinese giant paddlefish (Psephurus gladius) would never have made it onto a list of the world’s most beautiful endangered species. But its demise has turned it into a poster child for the dire conservation status of the world’s last remaining pool of megafauna.
We are used to thinking of megafaunal extinction as something that happened many thousands of years ago, as humans spread around the world and, probably not coincidentally, ran into the last mammoths, ground sloths, giant flightless birds and many more. Some terrestrial megabeasts survived, but in the past 50,000 years about two-thirds of these species . One place where they survived was in freshwater, probably for the same reason that we ignore them today. “They are hidden below the surface of human perception,” says Jähnig.
But if we looked, we would be amazed. There are 206 living freshwater megafaunal species – defined as those that can exceed 30 kilograms, about the size of an adult golden retriever. Three-quarters of the world’s major river basins are home to at least one, with the Amazon, Congo in Africa, Orinoco in South America, Mekong in South-East Asia and Ganges-Brahmaputra basins especially rich in them.
Many can grow much bigger than the 30 kg lower limit for this oversized club. In 1931, a Chinese biologist claimed that paddlefish in the Yangtze near Nanjing, China, could reach 7 metres in length, although the largest recorded in more recent decades before they vanished are only about half that. That is still a very big animal (see “The river giants”). The largest freshwater fish in the world is the beluga sturgeon (Huso huso), which is can reach . A small adult whale shark is about the same size.
Final swimmer
The Chinese paddlefish was one of two remaining species of an ancient lineage of fish (Polyodontidae) that evolved in the Jurassic and survived the extinction of the dinosaurs. The last one swimming is now the American paddlefish (Polyodon spathula), which is found in small numbers in the Mississippi river basin.
Its Chinese cousin had been in trouble for years before finally gasping its last. They were once common, with around 25 tonnes caught every year for food. But a in Sichuan province in the summers of 1974 and 1975 found that large specimens were already rare, a fact that was attributed to overfishing.
In 1981, the huge Gezhouba hydroelectric dam was built across the Yangtze, preventing paddlefish from migrating upstream to their ancestral spawning grounds. This seems to have been the last straw for a species already under pressure from overfishing, habitat destruction, shipping and pollution. The – a 3.6-metre-long female – was unexpectedly caught in 2003 near Yibin in central China. A rescue programme was launched in 2005, but didn’t work, and an extensive survey of the entire Yangtze basin in 2017 and 2018 failed to locate a single one of these fish. “Given that there hasn’t been a reliable sighting for so long, there’s not much hope,” says extinction biologist Dave Roberts of the University of Kent, UK. In all likelihood, the last one actually died between 2005 and 2010 and the species was functionally extinct – that is, unable to reproduce – by 1993. There are no specimens in captivity and hence no prospect of a comeback. The scientists who broke the news described the extinction as a “reprehensible and irreparable loss”.
It isn’t the only large animal to have disappeared from the Yangtze in living memory. The baiji, aka the Yangtze river dolphin (Lipotes vexillifer), hasn’t been sighted since 2002 and is too.
Others are going the same way. The paddlefish’s close relative, the Chinese sturgeon (Acipenser sinensis), is on the , as are the Chinese alligator (Alligator sinensis), Chinese giant salamander (Andrias davidianus) and the Yangtze giant softshell turtle (Rafetus swinhoei).
Smaller fish are also in trouble. There are ; the paddlefish survey failed to find 140 of them. Most of these are probably highly endangered, according to the team from the Chinese Academy of Fishery Sciences which carried out the survey.
The annihilation of the Yangtze biosphere is entirely down to human activity. Since the 1950s, the 6300-kilometre river – the longest in Asia – has undergone explosive development. A third of China’s population, some 400 million people, live close to what is now the world’s busiest river; there are more than 40 cities beside it including the vast metropolises of Chongqing, Wuhan, Nanjing and Shanghai. Until the Gezhouba dam opened in 1981, it was free-flowing; other dams including the immense Three Gorges have since been added and or under construction.
And there is more to come. In 2016, the government unveiled the to promote further development. In the face of this immense pressure, the paddlefish survey scientists recently warned that the Yangtze aquatic ecosystem is in danger of collapse.
The Yangtze is just a drop in a very large freshwater ocean. All over the world, freshwater ecosystems and their megafauna are in trouble. According to a , “They are among the most threatened ecosystems globally”.
Some river systems are in even worse shape than the Yangtze. On a measure of threat to biodiversity, the Yangtze scores 0.822. Worst of all is the Danube (0.912), closely followed by the Mississippi (0.900), Shatt al-Arab (0.898) and the Orange (0.858). According to another , even though rivers and lakes (excluding wetlands) cover just 1 per cent of Earth’s surface, they harbour around a third of all vertebrates and half of fish species. Freshwater vertebrates are declining faster than their terrestrial and marine cousins.
Despite this, freshwater ecosystems are neglected in conservation policy. They really ought to be seen as a separate – and uniquely vulnerable – category alongside terrestrial and marine ecosystems, but are usually just lumped in with the former. “If you look at how freshwaters are represented in conservation frameworks, they lack their own goals,” says Jähnig. Freshwater biologists were planning to lobby the 2020 UN biodiversity conference in China for better recognition, but the meeting has been postponed until at least 2021 because of the covid-19 pandemic.
The animals bearing the brunt of this neglect are the 80 or so species of really big fish – not just sturgeons, but also giant catfish and carp, electric eels, lungfish, freshwater rays, river sharks and more. Since 1970, their populations have declined by 94 per cent on average. Most of them are endangered; some are probably doomed.
Vital yet vulnerable
These aren’t just aesthetic losses. Ecologists regard megafauna as . Large animals, for example, eat and excrete a lot and so are vital for the nutrient cycling that other, smaller species rely on.
Big fish are especially vulnerable for a number of reasons, says Jähnig. “They reproduce really late [in life] so they need to have the right conditions for a long time; some need 10 or 15 years to mature. They have relatively few offspring, and they require a big habitat. Many are migratory, so they wander up and down stream and that means if there is a barrier like a dam, they get into trouble.”
“There are multiple threats,” agrees Jarić. “Damming, pollution and big pressure from the human population.” That includes being hunted for food. Overfishing helped to see off the Chinese paddlefish, and has reduced megafish populations in the Mekong – the most heavily fished river system in the world – to “close to zero”, says Jähnig. In this part of Asia, species in the firing line include the Mekong giant catfish (Pangasianodon gigas), giant Siamese carp (Catlocarpio siamensis) and shark catfish (Pangasius sanitwongsei).
Overfishing has also been the scourge of sturgeons (see “Caviar catastrophe”). But despite this generally gloomy picture, there are glimmers of hope. The near-certain extinct status of the Chinese paddlefish, on top of the earlier loss of the river dolphin there and the generally rotten state of the Yangtze, seems to have focused the minds of the Chinese government, says Jarić, who works closely with freshwater biologists in the country.
“The paddlefish was a wake-up call in China,” says Jarić. After this, he says, there was a meeting between researchers working on fish in the Yangtze, the International Union for Conservation of Nature, conservation group WWF and the government to develop some new actions. “There seems to be a will to protect the Yangtze’s fish stocks and ecosystems,” he says. “So there could be positive effects from this.” One immediate action was a in 332 designated areas, which will be extended to the whole river and all of its tributaries next year. That is a start, says Jarić, but fishing bans don’t always work and can make matters worse. “If there is not good control, people just switch to illegal fishing, and then there’s even less control.”
And fishing bans don’t address the bigger issue of dams. New ones usually have fish gates to allow migratory species to swim freely up and down stream, but they rarely work as well as advertised, says Jarić. “Even if they are constructed, they are usually not as efficient as we want, some migration occurs through them, but not as much as is needed.”
Dams remain an issue for river animals worldwide. A found that only 37 per cent of those over 1000 kilometres are completely free-flowing. These are restricted to the Amazon and Congo basins and remote regions of the Arctic. “It’s pretty unrealistic to say don’t build any dams,” says Jähnig. “But if we really want to build them – which is really a questionable thing, they have so many negative effects – can we move them to a certain part where maybe biodiversity won’t be that much affected?”
Despite these obstacles, efforts to save the megafish are under way. In Europe, for example, sturgeon restoration projects are gathering momentum. The last remaining wild population of the European sturgeon – which 150 years ago was common in every major river system connected to the North Atlantic, including those in the UK – is clinging on in the Gironde river in France. Ditto the Adriatic sturgeon in the Po in Italy. Captive breeding programmes are attempting to restore those populations to healthier numbers, while programmes are also under way to to rivers in Poland and Germany. Whether these can succeed isn’t clear, says Jarić. “We don’t know if they can establish stable populations, the rivers are still heavily fished, polluted and degraded.”
“The animals bearing the brunt of this neglect are the 80 or so species of really big fish”
In the Americas, the picture is brighter. “The Amazon river basin is reasonably fine still,” says Jähnig. On the Juruá river, which feeds into the Amazon in Brazil, sustainable fishing projects have even allowed the pirarucu, an air-breathing megafish, to make a .
In North America, strict conservation measures have allowed other species to turn the corner. The Alabama sturgeon is probably lost and gone forever, but the lake and Atlantic sturgeons are showing signs of recovery. “None of them are really doing well,” says Jarić. “They are still critically endangered, but many populations have a positive trend.”
In the Mississippi, meanwhile, another critically endangered megafish seems to have dodged extinction and has a shot at recovery. The US river is even more degraded than the Yangtze, but somehow its own weird fish, the American paddlefish, is doing relatively well. The loss of its Chinese cousin remains a reprehensible and irreparable loss. But maybe after 50,000 years of big animal extinctions at the hands of one uniquely destructive megafauna, we are finally learning to look after the giants that remain.
The river giants
Many rivers around the world were once home to megafish longer than 2 metres, but they are now a rarity. Here are some of the biggest:
Beluga
Status: Critically endangered
This sturgeon is the world’s largest freshwater fish, found in the Black, Azov, Caspian, and Adriatic seas and their tributaries. The largest was over 7 metres, but the average is around 2 metres
Giant Chinese paddlefish
Status: Extinct
Once common in the Yangtze river, China, this fish grows up to 3.6 metres and possibly even double that length
Pirarucu
Status: Recovering from overexploitation
This air-breathing fish from the Amazon river can grow larger than 3 metres
Caviar catastrophe
Sturgeon – long-lived fish with a shark-like fin on their back — used to be common across Eurasia and North America, but demand for their roe in the form of caviar has reduced them to a few diminished and often unsustainable populations. Between 1985 and 2005, the sturgeon population in the Caspian Sea – the source of 90 per cent of the world’s wild caviar – collapsed. Even today, sturgeon poaching is big business, even though there are hardly any fish left.
“Poachers face high punishments, but the money they can earn is a big motivation,” says Ivan Jarić at the Czech Academy of Sciences Institute of Hydrobiology. “They can get rich from a single catch.” One beluga sturgeon can supply 60 kilograms of caviar worth €30,000 to the poacher. And as sturgeon species get rarer, the price spirals ever upwards. These fish are now farmed for caviar, but connoisseurs say it is an inferior product. “Illegal fishing is very profitable and hard to control,” says Jarić.
Article amended on 2 October 2020
Correction: We have changed a photo in this feature because the original was showing the wrong species of paddlefish.
