Chinook Salmon Recovery on the Post-Dam Elwha River

Tholen Blasko

doi:10.7273/000003760

The Elwha River is a Puget Sound tributary that historically contained one of the richest salmon runs in the contiguous United States. The Chinook salmon (Table 1) native to the river were known for their large body size and are thought to have once grown to over 100 pounds. Two dams were constructed in the Elwha River. The Elwha Dam in 1913, and the Glines Canyon Dam in 1927. The Elwha Dam was constructed eight kilometers (km) from the mouth of the Elwha and had no fish passage capabilities. Anadromous species were therefore limited to an 8km migration while the dams were in place. Chinook salmon populations and average individual size both decreased with the dams in place. The dams also acted as sediment and woody debris traps and altered river temperatures and floodplains. The 8km of riverbed below the dam coarsened during this time due to the lack of sediment flow. In 1992, congress passed the Elwha River Ecosystem and Fisheries Restoration Act, which called for the decommissioning and removal of both dams, as well as mandating a complete restoration of the Elwha River ecosystem and native anadromous fisheries. As a result, the Elwha Dam was removed in 2011, followed by the Glines Canyon Dam in 2014. The removal of the dams triggered a sediment pulse that released a majority of the trapped sediment and small woody debris and expanded the delta at the Elwha’s mouth. Post dam removal, the Elwha experienced periods of lethal turbidity and a rockslide near the previous location of the Glines Canyon Dam that temporarily blocked fish passage until 2015. This project examines published literature, agency reports, and performs interviews to take a holistic look at the state of recovery for Chinook Salmon in the Post-dam Elwha river system. This is an important and relevant topic to study as dam removal increasingly emerges as an option for river restorations. The relative infancy of ecosystem recovery post dam removal should be considered due to the generation time of chinook salmon and residual turbidity after the project’s completion. There are indications that chinook salmon are recovering on the Elwha River. First, individuals were observed above the location of the Elwha dam a year after it was removed. Second, there were signs of recolonization above the Glines canyon dam until the 2015 rockslide. After passage was restored, Chinook were observed increasing their range in the middle and upper reaches every year. Chinook have also been observed recolonizing tributaries as far upriver as the Hayes River, a tributary that flows into the Elwha 51km from the mouth. The ratio of hatchery to natural spawning Chinook has been an area that has struggled to improve, with only 4% of the total Chinook population spawning naturally. Researchers are aiming for a 95% natural spawning population before any alteration to hatchery production will take place. With an average five-year generation time, the first complete cohort of Chinook that experienced no artificial or natural barriers in their migration is currently nearing completion. With a decreased straying rate, increased range in the river, and no angling pressure, there has been optimistic signs of recovery since the removal of the dams, and great potential for further recovery in the next decade.

Chinook Salmon Recovery on the Post-Dam Elwha River

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