March 21, 2008

Fish Impacts on Frogs - the Tip of the Iceberg

The removal of trout populations from lakes and streams in California to restore mountain yellow-legged frogs (see has generated a fair bit of controversy over the years. Much of the controversy stems from differences of opinion about the degree to which introduced trout are a primary cause of mountain yellow-legged frog declines, and therefore whether such removals in fact benefit frog populations. These are important debates, but miss the bigger picture entirely. That is, introduced trout have dramatic impacts not just on amphibians, but on aquatic ecosystems in general, and frogs are only one component of many in these ecosystems.

Numerous studies have shown that trout introduced into naturally-fishless habitats fundamentally alter the way these ecosystems function. Trout introductions change nutrient cycles and algal biomass, eliminate (or greatly reduce the abundance of) conspicuous invertebrates and amphibians, and sever connections between aquatic and adjacent terrestrial ecosystems. As an example of this latter effect, ongoing research indicates that aquatic insects emerging from lakes and streams are important prey for a host of terrestrial predators, including birds. Nonnative trout eliminate many of these aquatic insects via intense predation, and as a consequence alter the distribution of birds. These impacts are widespread in California's wilderness areas and national parks, areas set aside to protect natural values and processes. As such, these ecosystem-wide impacts are impossible to ignore.

Finding solutions that effectively mitigate the unintended consequences of fish introductions will require stepping back from a narrow fish-frog focus and taking a broader view that acknowledges that frogs are but one facet of a many-faceted issue.

Back to The Mountain Yellow-legged Frog Site.

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