Fish on the Move: Rescuing Salmon During Muir Woods' Redwood Creek Restoration

By Tim Smoot, Scientists in Parks intern, San Francisco Bay Area Network Salmonid Monitoring Program, September 2023.

A juvenile coho salmon moved out of the construction area. NPS.

The second phase of a major restoration of Redwood Creek in Muir Woods National Monument, meant to improve habitat for salmon and trout, is under way.

Why the creek needs help

In the 1930s, the Civilian Conservation Corps lined the creek's banks with large boulders and removed woody debris to stabilise the banks and prevent erosion, hoping to protect the famous redwoods. The trees did not need it — and the changes disturbed the natural flow, leaving the creek straighter, shallower and more uniform.

The creek is home to federally endangered coho salmon (Oncorhynchus kisutch) and threatened steelhead trout (O. mykiss), whose young depend on deep pools and large woody debris for cover. The project removes the boulders and installs large pieces of wood. Results from the first phase confirmed that this restores a meandering flow, creates deep pools and gives young fish cover.

Moving the fish

To remove boulders and place wood, sections of the creek were drained, the flow diverted through large pipes. Before the heavy machinery arrived, the network's coho and steelhead monitoring team cleared the construction areas of fish and other aquatic animals — coho, steelhead, sculpin (Cottus species) and California giant salamanders (Dicamptodon ensatus) — and moved them to parts of the creek still flowing.

They used two tools:

• Seine nets, as wide and deep as the stream, drawn around the fish to lift them out.
• Electrofisher backpacks, which put a mild electric current into the water to stun fish briefly so the crew can scoop them up with hand nets.

In one construction area alone, the team caught and relocated more than 25 coho salmon and 100 steelhead, over 1,100 sculpin and around 170 California giant salamanders. Now they are eager to see how salmon use the improved habitat in the Muir Woods stretch of Redwood Creek in the years ahead.

More information

• San Francisco Bay Area Network salmonid monitoring: https://www.nps.gov/im/sfan/salmonids.htm
• Pacific Coast Science and Learning Center, coho and steelhead: https://www.nps.gov/rlc/pacificcoast/coho-steelhead.htm

Sources

• National Park Service, San Francisco Bay Area Network, "Fish on the Move During Redwood Creek Enhancement Project," by Tim Smoot. https://www.nps.gov/articles/000/sfanblog_fish-on-the-move-during-redwood-creek-enhancement-project.htm
• Redwood Creek salmon habitat enhancement: https://www.nps.gov/articles/redwood-creek-salmon-habitat-enhancement.htm
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