Glacier National Park reshuffles native trout

The move will protect species at risk from climate change and invasive fish in new habitats.


Montana’s famed native trout are under siege. Not only do temperature-sensitive species like bull trout and westslope cutthroat trout face growing risks from climate change, they’re being pushed out of their habitat by non-native species.

The problem has reached crisis levels in Glacier National Park, where Chris Downs, the park’s supervisory fisheries biologist, says 10 of the 17 lake systems west of the Continental Divide have been compromised by non-native fish – the decades-old legacy of stocking species meant to please anglers in area waterways. Lake trout are of chief concern, competing with and preying upon bull trout, but non-native rainbow and brook trout are wreaking havoc as well, outcompeting and hybridizing with native species, disrupting their genetic integrity.

In Glacier National Park, bull trout have been pushed to the brink of extirpation by non-native lake trout. Park fisheries managers are now aiming to move bull trout and other species to new refugia.

The looming specter of climate change magnifies threats to native trout, as it's expected to alter precipitation and disturbance patterns and warm many water bodies above what they can tolerate. Park managers are taking action with a new management plan that aims to expand efforts to move native trout to new habitat, or refugia. Officials hope the new destinations, often tucked in higher-elevation locales that were previously inaccessible to fish, will allow “clean,” genetically pure populations to establish themselves free from the threat of non-native fish species and better insulated from rising temperatures.

The deliberate movement of native species out of their historic ranges and into new habitats is part of a move toward adaptive management, an approach officials say is better suited to address stresses now and in the future. “Management has shifted from a reactionary approach to a proactive approach,” says Clint Muhlfeld, an aquatic ecologist for the U.S. Geological Survey. “(Hockey great) Wayne Gretzky said, ‘Skate to where the puck’s gonna be, not to where it’s been.’”

Implementation of the strategy has already begun. In 2014, Muhlfeld and an assistant lugged 111 young bull trout in backpack water containers from Logging Lake five miles up-drainage to Grace Lake, until then off-limits to all fish thanks to a waterfall blocking upstream migration. “In just three decades, in some cases, lake trout had totally overwhelmed these systems,” Muhlfeld says. He says that, in some parts of the region, native bull trout are so greatly reduced in numbers that they have likely been “functionally extirpated.” While westslope cutthroat trout are recognized as a species of special concern within Montana, bull trout are listed as threatened on the federal endangered species list.

Now the tactic, known as translocation, will be extended to threatened fish in other water bodies of the park, depending on the outcome of various rounds of public comment and environmental impact assessments – an approval process which may stretch until 2018. Citing Glacier’s marquee, top-of-the-continent location as an otherwise ideal climate refuge, Downs is hopeful that native trout have a shot if put in a setting where introduced species are out of the equation. “They have some natural ability to deal with the environment if they don’t have constant other pressure from non-native fish.”

The management plan entails more than simply shifting trout species around. Downs says the project eventually looks to encompass the whole park and all its native fish species. Besides relocating native fish, efforts to remove introduced species through use of netting or chemicals will also continue, and some lakes – instead of having fish introduced – will be allowed to revert to their natural, fishless state. 

111 bull trout were backpacked from Logging Lake to Grace Lake in Glacier National Park in 2014. Officials are currently working to expand similar efforts, known as translocation.
Courtesy of National Park Service

The park’s fisheries biologists will closely monitor the success of their translocation efforts and adjust their management accordingly over time. For now, the scientists stand by the strategy’s innovative premise, arguing that given the grave threats facing native fish populations, drastic measures are necessary.

The effort may be one of the first examples in the West of wildlife managers taking climate change into account and shepherding species to new areas where more resilient populations might be established. But, in an era of accelerated, climate-driven upheaval, land managers may need to take an increasingly hands-on approach and nudge species in the right direction – or risk losing them entirely.

“We’re entering a century of dynamic disequilibrium,” says Muhlfeld. “The management decisions now in the next couple decades are going to be important for protecting future biodiversity.”

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