Pablo Jusim was living the dream in Tierra del Fuego. From 2015 to 2018, he spent his days trekking through the jagged landscapes of the Martial Mountains, walking along rivers through the wild forests and steppes of the southern tip of the Americas.
The experience was idyllic—until he encountered the invasion and its consequences. “The first area where I saw beavers was a tree cemetery,” he said. “It’s sad to see in a sector a very beautiful forest, then near the rivers, a dead forest,” said Jusim, a biologist with Argentina’s National Scientific and Technical Research Council (CONICET).
Jusim was checking beaver (Castor canadensis) traps set out as part of a pilot project to get a sense of whether managers could eradicate the invasive animals from the Argentine part of Tierra del Fuego’s biggest island, a 28,400-square-mile piece of land bigger than West Virginia that sits south of mainland Chile and Argentina. His findings revealed pathways to potential success as well as mountain-sized obstacles in an effort that’s just getting off the ground.
“Technically, it’s viable to eradicate beavers from South America—one of the biggest eradications in the world if we achieve it,” Jusim said.
Creating a trapper’s paradise
Wildlife managers introduced just 20 beavers from Canada to Tierra del Fuego and other parts of Patagonia in 1946 to bolster the fur trading industry. They reasoned that the climate was similar to parts of Canada and the northern United States, where beavers thrive in their native range. For the first three decades, beaver hunting was banned so the population could grow—and did it ever. Numbers took off, but changes in fashion over the next 30 years led to a reduction in pelt prices. In addition, the environment in much of Tierra del Fuego is so rugged that prospective hunters had a hard time accessing the beavers in the first place. Interest in hunting beavers plummeted.
Their numbers continued to increase, though, and by the 1990s, they had even made the jump from the island of Tierra del Fuego to Chile’s Brunswick Peninsula on the mainland. In the following decade, the governments of Chile and Argentina began to think about solutions, such as paying hunters to cull the invaders.
Invasive engineering
When beavers dam waterways in Canada or the U.S., their ecosystem engineering may change the landscape, but it isn’t as destructive to native species, many of which are adapted to taking advantage of the slow-moving water and wetlands that beavers create.
But in Patagonia, species aren’t adapted to take advantage of these alterations and face challenges when the critters are around. Patagonian trees, for example, will get drowned out and die—the reason Jusim could tell he was approaching a dam well before he would actually see it or any other signs of beavers.
While beavers are likely to cause downstream—and upstream—ecological effects, research on these impacts is limited in Tierra del Fuego. Anecdotally, Jusim said that the wetlands open up some foraging habitat for ducks and waterbirds, while the drowned-out beech trees may provide some nesting or foraging habitat for woodpeckers. But dams are likely to impede aquatic life.
Stopping the Patagonian beaver invasion
In 2014, the Argentine government started an eradication pilot project. Jusim, conducting his PhD work at the University of Buenos Aires at the time, analyzed the results of this project in a study published recently in the Journal of Wildlife Management.
The project occurred between October 2015 and June 2018, and researchers focused on seven test areas. Ten trappers used a variety of techniques, including lethal traps and body grip traps, or snares, in different ecosystems on the Argentine side of Isla Grande de Tierra del Fuego. When trappers were unsuccessful using these techniques, they would sometimes shoot them.
Jusim traveled with the trappers, setting up trail cameras in six of the seven pilot test areas. Beavers aren’t picky about where they settle in Tierra del Fuego—they are found in nearly every ecosystem there, and a study in the 1990s found beavers had colonized 93-94% of rivers in the archipelago. As a result, Jusim had to hike mountains, along rivers and through Patagonian steppe, sleeping at ranches or camping in natural reserves along the way. “It was marvelous for me,” he said. “It’s really a dream to walk here.”
Altogether, the trappers worked in 505 beaver colonies and trapped or killed more than 1,000 beavers. Analysis of the different traps revealed that body-grip traps were the most effective, especially as they allowed eradication in several colonies simultaneously, and daily trap monitoring in remote areas isn’t necessary. They found that, ideally, traps should be set right on dams. They also found that dams should only be broken open after trappers capture the first beavers. Trappers also got better over time.
Jusim said they found it’s important to eradicate an entire colony to be effective. “If you leave even one beaver behind, the eradication fails,” he said. “You need to hunt all beavers in a place.”
Meanwhile, a companion paper published recently in Integrative Zoology and examining the same seven pilot projects found that a management strategy that focused first on adult removal, then on younger beavers, was likely to be the most effective.
At the same time, wildlife managers in Chile conducted a similar project, though Jusim and his colleagues only analyzed the Argentine part of the project in this study.
Beaver eradication in Tierra del Fuego
Overall, Jusim and his colleagues estimated that it would cost about $31 million to eradicate the beavers from Argentine Tierra del Fuego over 17 years.
They found that the removal effort becomes a lot harder in certain ecosystems. For example, in the mountain zone, specialists had to put out an average of 23 traps per kilometer of waterway to catch one beaver. This was unfortunate because the beaver density was higher in mountain zones compared to other ecosystem types.
Meanwhile, the cost was so prohibitive that the team couldn’t work in a peat bog zone in the west of Argentine Tierra del Fuego due to its remoteness and inaccessibility.
The work was easier to conduct in the steppe areas, which are flatter and have ranch areas that make beaver wetlands easier to access, Jusim said.
Analysis of the trap types revealed some potential issues with unwanted bycatch as well. For example, Jusim said that the traps had to be small enough not to capture native species like cougars (Puma concolor). Also, in areas with southern river otters (Lontra provocax), wildlife managers could only use nonlethal traps and would have to visit them every day, as the International Union for Conservation of Nature considers the otters endangered. In general, this overlap between beavers and otters is only a problem in areas in river mouths near the sea, though, Jusim said.
Overall, the study revealed that eradication is technically feasible—though costly. “We only need a political decision to activate it for 20 or 30 years,” Jusim said.
This photo essay is part of an occasional series from The Wildlife Society featuring photos and video images of wildlife taken with camera traps and other equipment. Check out other entries in the series here. If you’re working on an interesting camera trap research project or one that has a series of good photos you’d like to share, email Joshua at jlearn@wildlife.org.
This article features research that was published in a TWS peer-reviewed journal. Individual online access to all TWS journal articles is a benefit of membership. Join TWS now to read the latest in wildlife research.
