Freshwater Animals Are More Fragile Than Thought, With Nearly a Quarter Threatened With Extinction, Study Finds

Freshwater ecosystems across the world are in distress. As scientists better comprehend the extent to which lakes, ponds, rivers and marshlands—and the animal and plant life they support—are suffering from long-term human intervention, their findings are often dire.

A new study published in Nature on Wednesday finds that nearly 25 percent of freshwater fauna—including species of fish, dragonflies, damselflies, crabs, crayfish and shrimp—are “threatened with extinction.”

“That means there are high to extremely high risks of becoming extinct in the future,” Catherine Sayer, lead of the freshwater biodiversity team for the International Union for Conservation of Nature (IUCN) and the lead author of the study, explains to ABC News’ Julia Jacobo. “That’s quite an alarming percentage.”

Although freshwater covers less than 1 percent of the Earth’s surface, it supports 10 percent of the planet’s known animal species, including roughly half its types of fish. For the study, researchers assessed 23,496 species of freshwater animals, determining that 24 percent were threatened with extinction. At least 4,294 species are considered at a high risk, according to a statement from the IUCN.

Their examined species spanned three groups: Ten-legged decapods like crabs, lobsters and crayfish are the most vulnerable, with 30 percent of their species at risk; fish come in second, with more than a quarter of them threatened; and odonates, like dragonflies and damselflies, which are aquatic during their larval phase, follow at 16 percent.

Stuart Pimm, a conservation ecologist at Duke University who was not affiliated with the study, calls it “a long-awaited and hugely important paper,” according to Christina Larson of the Associated Press.

The study finds human modification of the environment is a major factor in turning freshwater ecosystems into more vulnerable shells of their former states. Some 54 percent of the threatened species are affected by pollution, 39 percent by dams and water extraction, 37 percent by agriculture and 28 percent by invasive species and disease.

Major human alteration of freshwater habitats is hardly a new development. In the 12th century, for instance, the Dutch began to drain swamps to create tractable land for agriculture. Or, take Chicago, which sits along the coast of Lake Michigan, one of the Great Lakes that together host some 21 percent of the world’s freshwater. In 1900, engineers reversed the flow of the Chicago River, and 45 years before that, lawmakers decided to physically elevate the city from the swampland on which it was built.

But the trend has certainly accelerated in recent decades. The United Nations estimates that 35 percent of global wetland area was lost between 1970 and 2015—a rate three times faster than deforestation.

“Almost every big river in North America and Europe is massively modified” with dams, Pimm tells the AP, which threaten freshwater species by blocking migration routes, affecting sediment flow and altering downstream hydrology.

“Dams completely block water courses, which means that species can’t move downstream, and so they can’t get to habitats that they previously used for breeding or feeding,” Sayer tells ABC News. “And that completely disrupts the lifecycle.”

Even the paragons of the freshwater realm like the Amazon River might “appear mighty,” Patricia Charvet, a biologist at Brazil’s Federal University of Ceará and a co-author of the study, tells the AP. “But at the same time, freshwater environments are very fragile.”

The authors of the study emphasize that although threatened freshwater animals tend to live alongside threatened terrestrial and avian creatures, the risks to these water-dwelling species are different. So too must be the solutions.

Rajeev Raghavan, an ichthyologist at the IUCN and a co-author of the paper, offers the example of the Western Ghats, an Indian mountain range renowned for its biodiversity.

“Although they live side by side in the Western Ghats, conservation action for tigers and elephants will not help the critically endangered humpbacked mahseer,” Raghavan says in the IUCN statement. The large, freshwater fish “is threatened by habitat loss due to river engineering projects and sand and boulder mining, poaching and invasive alien species.”

Along with the Western Ghats, the paper identifies Lake Victoria in Africa, Lake Titicaca in South America and Sri Lanka’s Wet Zone as particularly species-rich—and threatened—freshwater regions.

“The particular value of this study is that it shows us which river basins, lakes, et cetera, are the ones where the conservation challenges are most urgent and serious,” study co-author Ian Harrison, a freshwater conservationist at Northern Arizona University and a member of the IUCN Species Survival Commission, tells Reuters’ Will Dunham. “It acts as a baseline of information from which we can track progress, to see if our actions are reducing threats.”

Since 1500, the study finds, 89 freshwater species have gone extinct—and an additional 178 are suspected to be gone. With the recently identified species now on the extinction watch list, Sayer says in the IUCN statement, “lack of data on freshwater biodiversity can no longer be used as an excuse for inaction.”

Eli Wizevich | | READ MORE

Eli Wizevich is a history correspondent for Smithsonian. He studied history at the University of Chicago and previously wrote for the El Paso Times.