Greg Hood is a researcher in western Washington who knows a few things about salmon habitat — a few surprising things. When Hood talks about preserving threatened populations, he doesn’t mention in-stream flows, fish ladders or water temperatures. Instead, he brings up a mostly-vanished ecosystem than once lined significant portions of the Puget Sound. It was composed of a shrub named sweetgale, tidal marshes and… beaver ponds near the seashore. That’s right, some beavers stake out seaside territory, and according to Hood, their ponds make excellent homes for juvenile salmon. Problem is, most of that tidal habitat has been destroyed over the last century or so. So little of it remains today that he thinks most people have forgotten — or have just never realized – how important the beaver ponds once were to the endangered Puget Sound Chinook.
The Seattle Times recently covered Hood’s work, and some of his research can be found online, but here’s the gist of his findings:
Hood works in the Skagit Valley, a ridiculously fertile swath of towns and farmland that lines a portion of the Puget Sound. These days the valley is famous for its tulips and filled with fields of corn, potatoes and other crops, but it wasn’t always that way. Before settlers diked the Skagit River and drained much of the tidal wetlands in the late 1800s, the river delta contained large marshy areas of “scrub-shrub wetlands.” One important shrub was sweetgale, a nutrient-rich plant that was a favorite food of insects. In turn, the salmon fed upon the insects the shrub attracted.
And beaver ponds brought the sweetgale, the insects and the salmon together. Most people only associate beavers with freshwater, but according to Hood, beavers will put up with salt concentrations as high as ten parts in a thousand (seawater contains closer to 35 parts per thousand). Historically, beavers have constructed low dams in narrow channels in the wetlands. Those ponds supported rich populations of juvenile salmon, and Hood explains that by pointing to the sweetgale. Not only does the shrub attract insects, it also overhangs the ponds, sheltering the salmon from the predations of great blue herons.
These days, only scraps of the ecosystem still exist. Hood thinks that about 95% of scrub-shrub wetlands have been drained from the Skagit delta, and surmises that the situation is similar in other large tidal marshes up and down the coast from Tacoma to Vancouver, B.C..
“Most people have never even heard of (the shrub wetlands). You come here, and get a sense of what used to be everywhere. And the next generation that never experienced it, they don’t even miss it.”
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