Dams help restore imperiled fish populations.
When Lewis and Clark made their way through the Pacific Northwest in the early 19th century, the streams were teeming with steelhead trout and beavers. But subsequent human activities, including harvesting beavers to near extirpation, led to widespread degradation of fish habitat.
Beaver dams are beneficial to fish in streams because they boost the diversity of habitats available to them and provide refuge from predators as compared to completely unimpeded streams.
Nonetheless, ecologist Nick Bouwes, owner of Utah-based Eco Logical Research, Inc. and adjunct assistant professor at Utah State University, tells The Science Explorer that the “benefits of beavers to trout and salmon has been debated and beaver dams are often removed to improve fish habitat.”
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In a 7-year experiment, Bouwes and his colleagues built their own versions of beaver dams, known as beaver dam analogs (BDAs), by pounding wooden posts into the stream bed and weaving willow branches between the posts, throughout the highly degraded streams within Oregon's Bridge Creek Watershed.
Beavers quickly built on the BDAs, resulting in an increase in natural dam construction and longevity in Bridge Creek, according to the study findings published in the journal Scientific Reports.
“Beavers like to anchor their dams to something, often to large pieces of wood and trees they cut down, but since there is no more large woody material in Bridge Creek they built dams on our BDAs,” Bouwes explains.
The researchers also documented increases in fish habitat quantity and quality in their study watershed relative to the watershed that received no BDAs. The changes in habitat in the watershed receiving BDAs resulted in a significant increase in population, survival, and reproduction of the threatened steelhead trout inhabiting the streams.
“We contend that beavers and trout/salmon have coexisted for thousands to millions of years,” says Bouwes. “If we can help beavers get established they can do a lot of the heavy lifting for us to restore streams, saving money that can be used for other conservation efforts.”
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