Artificial beaver dams saw juvenile coho salmon survival rates go from 8% to 60%

Beaver dams, once a natural feature of the Scott River valley in northern California, have been recreated through artificial structures to improve the survival rate of juvenile coho salmon. Prior to European fur trappers trapping and killing beavers in the 1830s, these dams created an extensive riverine wetland that provided habitat for coho salmon and various wildlife.

After the beaver population was nearly wiped out, a nonprofit called the Scott River Watershed Council built two artificial dams on tributaries called Sugar Creek and French Creek in 2015. These wooden posts, interwoven with branches and plugged with gravel, straw, and mud, have since been supplemented by beavers who have repaired and expanded the structures.

The restored habitats, which cover around 9,000 square meters, maintain cooler water temperatures, preventing stress and promoting the growth of juvenile salmon. Survival rates for coho salmon in these artificial habitats increased from 8% before the dams were built in French Creek to 60% afterwards. The presence of coho salmon in the Scott River has also returned to levels seen in other rivers monitored in the study, even during severe drought.

While the artificial dams have proven to be a cost-effective solution, their success highlights the importance of allowing beavers to thrive in their natural roles as ecosystem engineers.