Wednesday, January 14, 2015

Natural Recolonization Works for Salmon following Dam Removal

Salmon and steelhead have evolved in a landscape in the Pacific Northwest rife with peril. From landslides and volcanoes, to glaciers which have intermittently advanced and retreated throughout the region over the last few million years. Under these evolutionary circumstances it is not surprising then that salmon have the ability to colonize newly available habitats. Indeed straying and colonization by salmon could be considered one of the very cornerstones of the species. A recent article in the Columbia Basin Bulletin highlights this point, presenting research from the Cedar River, Seattle's municipal watershed, that has shown convincingly that when passage is restored into areas above dams salmon will naturally recolonize the habitat quickly. Landsburg Dam on the Cedar River was built in 1901 as the diversion dam for Seattle's drinking water. In 2003 the city built a fish ladder over the dam following the ESA listing of Puget Sound chinook and growing concern over salmon recovery in the region. At the time there were some vocal advocates for using hatcheries to reintroduce salmon above the dam, but ultimately cooler heads prevailed and the city opted for the lower cost, natural option of letting salmon recolonize the habitat on their own.

They also teamed up with researchers from UW and NOAA who tracked the recolonization process from the very beginning. What they found, while not surprising, should help inform the debate around salmon recovery all over our region. In just a few generations coho and Chinook had established populations above the dam. Coho, which rear for a year or two in freshwater prior to their seaward migration benefited the most from the access to 30 miles of intact habitat that the fish ladder provided. Today hundreds of coho spawn above the dam every fall and with each passing generation the population continues to grow.

More information in the CBB: