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Salmon Fish Passage at Beaver Dams

Beaver co-evolved with Atlantic and Pacific salmon in the same freshwater streams over millennia. All are critically important Keystone species who create tremendous benefits for myriads of other species. Recent scientific studies by Dr. Michael Pollock at NOAA and many others have scientifically proven what is intuitively clear, that beaver dams have a net beneficial effect on salmonids, improving their growth, survival, and now their recovery. In addition, studies with PIT tagged juvenile salmon have proven they regularly travel in both directions over beaver dams. For all these reasons, beavers and the nursery habitats created by their dams are now highly prized in all salmon producing waterways in the Pacific Northwest.

Since beaver dam benefits are so significant, on the west coast when beavers are scarce or streams are badly incised, salmon and watershed restoration specialists are building Beaver Dam Analogs (BDA) to imitate the dams that beavers build naturally and for free. Even these man-made beaver dams are showing positive effects on salmon recovery.

There are challenges however. Beaver damming of road culverts as well as many of the flow devices used to manage beaver damming can create barriers to salmonid movement. In addition, precipitation reductions and storm pattern changes due to climate change are adversely affect juvenile and adult salmon movement in many areas of their range.  For these reasons beaver flow management devices needed adaptations to improve salmon passage.

In 2013 Mike Callahan and a team from Snohomish County in Washington state partnered to install an innovative flow management device prototype designed to allow adult Coho salmon to easily migrate upstream past two beaver dams. The fish-friendly flow device is called the Snohomish Pond Leveler and it was a great success! Click HERE to see this salmon passage flow device in action.

The bottom line: More Beavers = More Salmon

Beaver Dam Challenges to Salmon

  • Fish passage over dams at low stream flows
  • Blocked road culverts
  • Sedimentation of some gravel redds
  • Nevertheless: More beavers = More Salmon

Beaver Dam Benefits to Salmon

  • Increased food for salmonids in beaver ponds
  • Slow water refuge conserves energy
  • Deeper, colder water in dry periods
  • Woody debris in stream
  • Bottom line: More beavers = More Salmon
  • Increased winter survival in streams with beaver dams
  • Faster growth of fry and juvenile salmon
  • More places of refuge for fry to feed and escape predation
  • Higher salmon returns in streams with beaver dams
  • Bottom line: More beavers = More Salmon
  • Improving Salmon Passage at Beaver Dams
    • More Snohomish Pond Leveler study sites needed.
    • A Juvenile Fish Passage prototype also ready to study.
    • Member – Salmonid Restoration Federation, Atlantic Salmon Federation
    • Additional research partners and sites welcome.