Salmon and steelhead habitat restoration projects in the Pacific Northwest have frequently relied on the use of engineered logjams—logs that are cabled together and placed in rivers to create pools where young salmon can live and grow in their first year before migrating to the ocean. Monitoring programs that rely on fish counts have shown that these human-made pools function as intended by providing a healthy habitat for juvenile fish.
But do the logjams affect stream habitat beyond the areas of the pools? Could they benefit entire river reaches?
Carlos Polivka, a research fishery biologist with the USDA Forest Service's Pacific Northwest Research Station, studied the upper and lower basins of Washington's Entiat River to find out.
Many habitat restoration projects involving engineered logjams are installed along the Entiat River. Polivka and his research team conducted snorkel surveys of roughly 5 miles of river, covering 13 individual reaches. They found that the pools created by these logjams did attract young salmon and not at the expense of other parts of the river where no restoration projects had been installed—the rearing capacity of broad sections of river was enhanced.
The research can be applied when planning habitat restoration projects and provides conceptual and empirical tools for more rigorous monitoring programs to assess the outcomes of the projects.
Kirkland, John; Polivka, Carlos; Claeson, Shannon. 2021. If you built it, did they come? Evaluating the effects of stream restoration on fish populations. Science Findings 241. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.