High in California’s Sierra Nevada, a conservation project changed the future of a disappearing amphibian.
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project → change → amphibian
In 2001, staff at Sequoia and Kings Canyon National Parks began removing non-native trout from selected lakes and streams, restoring water bodies that had historically been home to mountain yellow-legged frogs but were naturally fishless.
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that → begin → frogs
By 2011, nearly 44,000 trout had been removed from 19 lakes, including complete removal from nine.
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trout → remove → nine
The results were striking: surveys in three restoration lakes recorded an increase from nearly 190 frogs and tadpoles to more than 18,800.
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surveys → record → 18,800
The National Park Service says the project helped restore ecological balance and placed the frog population in a stronger position to face other threats, including deadly fungal disease.
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project → say → disease
A fish introduced into fishless lakes
The mountain yellow-legged frog is native to the high country of the Sierra Nevada.
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frog → introduce → Nevada
These frogs evolved in lakes, ponds and streams where fish were naturally absent.
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fish → evolve → lakes
For thousands of years, the frogs’ life cycle developed without the pressure of predatory trout.
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cycle → develop → trout
Tadpoles could grow in shallow water, young frogs could move around the edges of lakes and adults could reproduce without constantly avoiding fish.
uncertain
adults → grow → fish
The situation began to change when people introduced trout into high-elevation water bodies.
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people → begin → bodies
From 1870 to 1988, several non-native trout species were stocked in lakes, ponds, marshes and streams across Sequoia and Kings Canyon National Parks.
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species → stock → Parks
The National Park Service says these included golden, rainbow, golden-rainbow hybrid, brook and brown trout.
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these → say → trout
The fish were introduced partly to create recreational fishing opportunities and attract visitors.
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fish → introduce → visitors
But the stocking programs altered ecosystems that had developed without fish.
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that → alter → fish
Trout did not simply become another species in the food web.
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Trout → become → web
They became powerful new predators in places where mountain yellow-legged frogs had few natural defences against them.
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frogs → become → them
Why the frogs declined
Trout affect mountain yellow-legged frogs in several ways.
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Trout → decline → ways
They eat tadpoles and small frogs, compete with frogs for insects and force the amphibians into smaller, lower-quality areas.
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They → eat → areas
The presence of fish can also separate frog populations.
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presence → separate → populations
When trout occupy lakes and connecting streams, frogs may be pushed into isolated ponds or narrow areas where they have fewer options for feeding, breeding and escaping environmental stress.
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they → occupy → stress
The National Park Service reports that mountain yellow-legged frogs have disappeared from 92 per cent of their historic range in the Sierra Nevada.
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frogs → report → Nevada
Both recognised species—the mountain yellow-legged frog, Rana muscosa, and the Sierra Nevada yellow-legged frog, Rana sierrae, have faced severe declines.
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species → recognise → declines
Chytridiomycosis, a fungal disease that attacks the skin of amphibians, also affected frog populations.
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that → attack → populations
Infected frogs can die because the disease interferes with essential skin functions.
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disease → die → functions
Trout reduced frog numbers and restricted their habitat, while disease threatened the populations that remained.
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that → reduce → populations
By 2014, both species had been listed as endangered under the federal Endangered Species Act.
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species → list → Act
The restoration effort begins
In 2001, park staff began removing trout from selected waters.
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staff → begin → waters
The work used large nets and electrofishing equipment.
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work → use → nets
Gill nets could capture fish in lakes, while electrofishers temporarily stunned fish so that crews could collect them.
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crews → capture → them
These methods allowed conservation teams to target specific water bodies without applying the same treatment across every lake in the parks.
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teams → allow → parks
The objective was not to eliminate trout from the entire Sierra Nevada.
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objective → eliminate → Nevada
Instead, the project focused on restoring selected ecosystems where removing non-native fish could provide immediate benefits for native species.
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removing → focus → species
By 2011, nearly 44,000 fish had been removed from 19 lakes.
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fish → remove → lakes
Trout were completely removed from nine of those lakes, according to the National Park Service.
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Trout → remove → Service
High-elevation lakes are often remote, and crews had to transport equipment across rugged terrain.
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crews → have → terrain
The process also required repeated visits because even a small number of remaining fish could eventually reproduce and rebuild a population.
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number → require → population
Removing the first wave of fish was only one part of the project.
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Removing → remove → project
Conservation workers continued targeting the remaining trout to prevent the restored lakes from being recolonised.
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workers → continue → lakes
The clearest sign of success came from Upper LeConte Canyon, a remote area containing lakes and streams where mountain yellow-legged frogs once lived.
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frogs → come → lakes
Park staff conducted summer surveys in three restoration lakes.
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staff → conduct → lakes
…and 62 more, not listed.
The Aporia
