To anglers across the globe, trout streams are characterized by free-flowing water that’s clear, complex, connected and, most importantly, cold.
Meanwhile, the trout that inhabit the waters, in addition to providing sustenance and recreation to millions of people, play critical roles in the health of ecosystems worldwide.
So what’s the piscatorial problem?
In the years ahead, the chilly streams that sustain Northwest Montana’s prized native fish — as well as trout habitat worldwide — are predicted to grow increasingly tepid as a result of rising global temperatures, threatening the sensitive aquatic species with “global extinction” unless more conservation studies take place at a local and planetary scale.
That’s according to a recent study published in the esteemed research journal “Science Magazine,” whose lead author, Clint Muhlfeld, works as an aquatic ecologist for the U.S. Geological Survey’s Glacier Park field office based in Glacier National Park.
The publication offers a lofty platform of scientific prestige that Muhlfeld hopes will draw broader attention to the plight of native fish and a multitude of trout species distributed throughout the world’s watery arteries, all of which share something in common — they are especially sensitive to rising temperatures.
Published in the May 25 issue of “Science,” the article, titled “Trout in Hot Water: A Call for Global Action,” marks the first worldwide assessment of trout species’ status. It found that a disproportionately high rate of trout species (compared to other vertebrates) are now threatened under the International Union for Conservation of Nature (IUCN) Red List, the world’s most comprehensive inventory of the status of biological species.
Of the 124 recognized species of trout, only 67 percent have been assessed by the IUCN, Muhlfeld said.
“Alarmingly, 73 percent of these species are currently threatened with global extinction, and four are now extinct,” he wrote in the “Science” article.
“Trout are like canaries in a coal mine,” Muhlfeld said in a recent interview, speaking by phone from Oslo, Norway, where he is working on a Fulbright Scholarship. “They are excellent indicators of disturbance, especially under climate change because of their sensitivity to temperature and freshwater stream flows.”
Native to all continents in the Northern Hemisphere, trout belong to seven genera (plural of genus), which are distributed across 52 countries. These cold-water specialists provide recreation and food to millions of people and play important roles in ecosystem functioning and health.
In an addition to serving as an economic boon — a recent federal analysis of outdoor recreation found that boating and fishing activities contributed $38.2 billion to the nation’s gross domestic product in 2016 — they are also excellent markers of an ecosystem’s health, Muhlfeld said.
“They are extremely sensitive to human disturbances because they require cold, clean, complex, and connected habitats for survival and persistence — all attributes that humans have substantially altered and degraded,” according to the study. “Despite their importance as societal icons and as indicators of biodiversity, many of the world’s trout species and lineages are endangered and some require immediate conservation efforts to reverse their precarious decline.”
Muhlfeld, along with a team of researchers, emphasized the need for swift courses of action to save “one of our most culturally, economically and ecologically important freshwater fishes.”
“Reversing these declines will require progressive conservation efforts to protect native trout diversity and ameliorate ongoing and future threats at local and global scales,” the study states.
Locally, Muhlfeld pointed to successful efforts by Montana Fish, Wildlife and Parks, which set out more than a decade ago to preserve and restore the westslope cutthroat trout fishery in the South Fork Flathead River.
Recognizing the pressure of hybridization with nonnative species like rainbow trout, the architects behind the South Fork Flathead Cutthroat Conservation Project began systematically removing nonnative fish and replacing them with genetically pure westslope cutthroat in 2007.
“Even though this is a global study, it stresses the need for conservation studies to take place at a local scale,” Muhlfeld said. “We know that hybridization is irreversible, and eliminating those sources that do long-term damage is a proactive strategy. Dealing with nonnative species like the South Fork recovery program that FWP implemented is a great example of that.”
Another example takes place in Glacier National Park, historically one of the last best strongholds for native cutthroat and bull trout. The biggest problem for these native species is that Glacier’s lakes and streams are brimming with nonnative fish, particularly invasive lake trout, which radiated out of Flathead Lake and colonized the park’s lakes, out-competing the native residents.
In 2009, biologists with Glacier Park and a USGS team led by Muhlfeld launched an experimental project on Quartz Lake, located in the park’s remote northwest corner, where lake trout invasion was still in its early stages of invasion. The aim was to reduce or eliminate lake trout by gillnetting, a project that required a boat to be helicoptered in and all of the supplies to be hauled in by biologists and mules.
Muhlfeld and his team first located so-called “Judas fish,” captured and radio-tagged them, then tracked the fish to spawning areas in order to capture and remove the densest concentrations of spawning lake trout.
The project has shown evidence of success in reducing lake trout, and is hailed as one of the first successful projects of its kind, standing out as a leading example that lake trout suppression, once thought to be futile, is possible.
“Only by addressing threats at their root causes can we accomplish these conservation goals,” Muhlfeld said.
Muhlfeld’s co-authors on the study were: Daniel Dauwalter, Ryan P. Kovach, Jeffrey L Kershner, Jack E. Willians, and John Epifanio.
To learn more about the study, visit science.sciencemag.org.