Freshwater species are at risk. A new global threat map could help save some from brink of extinction
A colourful new map that paints a not-so-rosy global picture of what's putting freshwater species at risk could help conservationists focus on threats and species most urgently in need of support.
Dams, farming, fishing, pollution, natural resource activity top Canada's threat list, McGill researcher says
Bryce Hoye · CBC News
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There's no shortage of threats facing Canada's aquatic creatures — whether it's dam activity linked to endangered white sturgeon losses in B.C. rivers, toxic tailing pond water poisoning wood frogs in Alberta, or agricultural runoff and zebra mussels throwing Lake Winnipeg's ecosystem out of whack in Manitoba.
It's slipperier to determine which human activity is most responsible for putting freshwater biodiversity at risk more generally.
"We know that freshwater wildlife populations are declining faster than terrestrial or marine species, and we also know that wetlands are shrinking way faster than forests," said Christophe Brabant, a PhD candidate at McGill University.
"We generally know pretty well which threats are impacting freshwater species, we don't really know where those threats are happening across the world."
That's the piece of the puzzle Brabant and others set out to answer in new research published in the journal Science that maps out "the geography of threats" leading to freshwater biodiversity losses around the world.
They reviewed known threats to over 2,100 freshwater species on the "red list" created by the International Union for Conservation of Nature (IUCN), which estimates a quarter of freshwater species are at risk of extinction. They then identified five groups of freshwater fauna facing risks — amphibians, reptiles, fish, mammals and odonates (dragonflies and damselfies).
Researchers created a global illustration of which threats appear to be the main drivers of declines. The result is a colour-coded map that shows threat intensity by region, and a companion index linking particular threats to declines in freshwater species.
"The map method … considers how different threats can affect different species rather than assuming that all species are affected equally," said Brabant.
The threat category with the highest impact in each subwatershed in the study shows a mosaic of differing threat intensities facing freshwater wildlife taxonomic groups across the world. (Submitted by Christophe Brabant et al.)
The activities topping Canada's threat list include: natural systems modification like dams and diversions, biological resource uses like hunting and fishing, agriculture, development, pollution, energy production and mining.
The leading threat identified globally was agriculture and aquaculture, particularly in the global south.
Pollution was the second most important threat category, especially in eastern China, India and across Europe.
Third was biological resource use, mostly in northern latitudes, including Canada and parts of sub-Saharan Africa and Southeast Asia.
One of the main takeaways, Brabant says, is that there can't be "a one-size fits all solution" for conservation to be efficient.
Dr. Madison Earhart, left, steadies a white sturgeon in British Columbia in 2024 as part of ongoing research into threats facing Canada's largest freshwater fish. (submitted by Madison Earhart)
What also stood out is the "huge accumulation of threats" in northwestern Africa and Europe, the lower Himalayas and the Missouri River basin, says Brabant.
In places with relatively large proportions of species facing extinction, he says they also found that "most of our threats had a higher intensity."
Climate change
On the map, disease and invasive species are represented by a green band that extends across several provinces near the Canada-U.S. border. Both forces are exacerbated by global warming.
Climate change, which is listed as the main threat only in small pockets around the world, isn't the leading cause of declines in Canada, according to the research.
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Brandon University researchers are searching Manitoba wetlands for frogs, toads and salamanders, expecting to find something they don't really want to see: signs of a fungal infection plaguing amphibians the world over.That could be more a reflection of limitations in the IUCN red list criteria to date than it is confirmation of climate change being a lesser threat, Brabant said.
"It's hard to know … that threat isn't recorded very well," he said.
One place it has been recorded well is at a network of kettle lakes in northwestern Ontario known as the Experimental Lakes Area (ELA), operated by the International Institute for Sustainable Development (IISD). There, scientists have been conducting experiments on real lakes since the 1960s to better understand how human activity impacts and threatens fresh water.
The lakes are far from other confounding variables that make it harder to tease out whether climate change is a major driver of declines.
"We're only beginning to understand what climate change impacts are on various species in isolation," said Mike Rennie, a research fellow with the ELA.
Last year, Rennie and others published research based on decades of consistent data collection to monitor water quality and biodiversity of species in one of the "reference" lakes at the ELA that remained otherwise untouched.
A scientist draws a blood sample from a lake trout as part of a decades-long water quality and biodiversity monitoring program on one of 58 kettle lakes that make up the Experimental Lakes Area in northwestern Ontario. (Submitted by IISD Experimental Lakes Area)
Their work showed air temperatures in the area rose by about 2 C between 1986 and 2016, and the duration of ice coverage on the lake shrank by nearly three weeks. During the same period, Rennie says there was a "notable decline" in the size of adult lake trout.
These cold-water fish that rise from the depths to chow down on minnows when the shallows cool down in the winter now have less time and space to hunt near shore.
"Nothing else is going on except we're seeing these changes in things like ice cover," said Rennie, adding that such changes are "sort of our best indicator of how climate warming is impacting these small lakes and these cold water fish."
The Noah's Ark problem
Frederik Noack, the Canada Research Chair in environmental economics, acknowledges there are constraints, like budgets and other competing priorities, that complicate how information from the threat map is applied.
He says this often results in questions about what criteria should be used to target conservation efforts that would provide the biggest bang for the buck.
"Just knowing there's a high intensity of threats on endangered species doesn't necessarily make that the target of conservation funding," said Noack, who co-leads the Wildlife and Conservation Economics Laboratory at University of British Columbia.
A beaver trudges across snow and muck and into the Assiniboine River in Winnipeg as ice recedes this past spring. The mammal that was almost driven to extinction due to the fur trade is now considered stable in North America by the International Union for Conservation of Nature. (Bryce Hoye/CBC)
He points to the Noah's Ark Problem, an economic model for biodiversity preservation from the late-1990s.
The analogy imagines how Noah, facing space constraints on the ark (think of this as the conservation budget), might choose which species survive and which are consigned to a watery grave, based on a desire to preserve as much overall biodiversity as possible while also factoring in the utility of each species to humanity and how likely they are to be rescued.
Noack notes the approach is very simplified, "but I think at least it gets the components right."
Critics of the model point to how it imagines species in isolation rather than sufficiently prioritizing the ecological role a given species plays that broadly benefits others.
The long-term survival of northern leopard frogs or Pacific salmon might depend on having a couple beavers aboard the arc to create wetland habitats other animals need to survive.
A frog lurks along the edges of a lake near the border of Manitoba and Ontario in September 2026. The IUCN red list estimates 25 per cent of global freshwater species are at risk of extinction. (Bryce Hoye/CBC)
As the story goes, Noah was instructed to only reserve space for land-dwelling creatures and birds.
Brabant says biodiversity conservation frameworks also overlook freshwater species.
He hopes the maps raise the profile of freshwater creatures and help decision-makers focus in on areas that most urgently need support.
ABOUT THE AUTHOR
Bryce Hoye is a multi-platform journalist with a background in wildlife biology. He has worked for CBC Manitoba for over a decade with stints producing at CBC's Quirks & Quarks and Front Burner. He was a 2024-25 Knight Science Journalism Fellow at MIT. He is also Prairie rep for outCBC. He has won a national Radio Television Digital News Association award for a 2017 feature on the history of the fur trade, and a 2023 Prairie region award for an audio documentary about a Chinese-Canadian father passing down his love for hockey to the next generation of Asian Canadians.
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