Resumption of Anadromy or Straying? Origins of Sockeye Salmon in the Elwha River

Abstract

When barriers to migration are removed, anadromous fishes from other rivers may colonize newly accessible habitat or landlocked forms of the species may resume anadromy if conditions allow. For example, two large hydroelectric dams on the Elwha River, Washington, were removed between 2011 and 2014 to restore populations of Pacific salmon Oncorhynchus spp. after a century of isolation. Immediately prior to and following dam removal (2010-2017), upstreammigrating adult Sockeye Salmon Oncorhynchus nerka were sampled, and DNA was extracted and compared with samples from the local Lake Sutherland population (above the lower dam's former location) and a coastwide genetic baseline to determine the probable origin of each fish. Genetic analysis indicated that none of the 45 Sockeye Salmon sampled had originated from the local population or other populations nearby in the genetic baseline, and only a single fish originated from the abundant and proximate Fraser River populations. The strays reflected two different sources and processes: 22 were from the west coast of Vancouver Island (all in 2015, when these populations were very abundant and encountered conditions unfavorable for upstream migration in their natal system) and another 22 assigned to more northerly populations, mostly to riverine populations from the Stikine River. Test fishery samples collected in the Strait of Juan de Fuca contained very few fish with assignments similar to these northern rivers. It is not clear whether these individuals originated from the distant riverine populations or from a closer population not in the baseline that resembles them genetically. Taken together, the findings indicate that the genetic composition of any future population in the Elwha River may reflect signatures from diverse sources and subsequent selection in the new habitat.

Leaf litter decomposition and detrital communities following the removal of two large dams on the Elwha River (Washington, USA)

“…Pre-dam removal salmonid population declines likely contributed to decreased primary productivity in the Elwha River due to nutrient limitation, as marine-derived nutrient inputs from salmonids are important for freshwater food webs across trophic levels (Duda et al, 2011;Tonra et al, 2015;Kane et al, 2020). As anadromous salmonids return to the Elwha (Kane et al, 2020;Quinn et al, 2021), we expect increases in productivity at all trophic levels and continued alterations to other ecosystem processes like organic matter processing. For example, we found highest levels of fungal at Lower Elwha sites, which could be related to greatest spawner densities.…”

Why does geography matter in big dam removal projects? Lessons from a comparison between the Sélune and Elwha River cases

“…The Elwha case study is based on an extensive review of scientific publications and grey literature (e.g. Duda et al, 2008;Pess et al, 2008;Crane, 2011;Sadin et al, 2011;Brenkman et al, 2012;Johnson, 2013;East et al, 2015;East et al, 2015;Warrick et al, 2015;Foley et al, 2017a;East et al, 2018;Brewitt, 2019;Morley et al, 2020;Hess et al, 2021;Quinn et al, 2021;Brown et al, 2022;Chenoweth et al, 2022), supplemented by a field visit to the restored sites and lengthy specific interviews with the project's managers (NOAA, NPS) conducted in April 2022. We did not meet with Lower Elwha Klallam Tribe representatives who were central players in the removal; we instead used various available peer-reviewed papers (e.g.…”

Life cycle management of natural infrastructure: assessment of state of practice and current tools

“…Consider the Pacific Northwest, where a central ecological goal is the re-establishment of regional anadromous salmonid populations. Historical habitats can be opened up by removing a dam, but this can lead to short-term recruitment of multiple species that may stray into the newly available habitats (Quinn et al, 2021). Such species-specific biological goals assume that reviving natural physical conditions will preferentially aid native populations recover across generations-processes that can occur quickly (Beheshti et al, 2021) or take decades (Wohl et al, 2015;Foley et al, 2017).…”