ÎçÒ¹AV

Investigating juvenile salmonid use of novel estuarine beaver dams in the Copper River Delta

2025 Research Seed Awards

PROJECT DESCRIPTION

Extending for over 75 miles along the Gulf of ÎçÒ¹AV, the Copper River Delta (CRD) encompasses over 2,800 km² and is one of the most contiguous and productive wetlands in North America. The CRD is a critically important ecosystem for migratory wildlife (Senner 1979), salmon (Simeone and Fall 2003), and people (Christensen et al. 2000). Traditional Eyak people have fished these waters for salmon since time immemorial. Today, the commercial Copper River salmon industry generates millions of dollars in annual revenue (Henderson et al. 2000). Additionally, personal- use and subsistence fisheries for consumption and exchange are cultural foundations for life in coastal ÎçÒ¹AVn communities.

The CRD is a dynamic coastal ecosystem that sits at the tectonic interface of two continental plates. In 1964, the 9.2 magnitude Good Friday earthquake permanently altered the hydrology and topography of the CRD by uplifting the outer coast 1.8 to 3.4 m in elevation (Reimnitz 1966). Consequently, previously saline habitats became more brackish due to the high outflow of glacial sourced freshwater. This tectonic uplift rapidly resulted in a complete shift in vegetation communities and restructuring of functional guilds along the outer CRD coast (Thilenius 1990, Boggs 2000).

Historically, beaver (Castor canadensis) exclusively occupied the inland glacial outwash plain among freshwater ponds, lakes, and streams, and avoided the coastal fringe due to tidal inundation and lack of woody vegetation (Roberds 1955). However, after the 1964 earthquake, beaver soon migrated outward to the coast colonizing ponds and sloughs following shifts in shrub-dominated habitat. While beavers were nearly extirpated across the continent through intensive trapping and currently persist at numbers far below historic levels (Wohl 2021), this post-earthquake range expansion in the CRD resulted in one of the most concentrated beaver populations in North America, with densities reaching 1.5 beavers/km² in the uplifted coastal margin (Morgan 1990). This high concentration of beavers altered coastal hydrology by damming up coastal sloughs, raising the water table, and flooding drainable areas (Cooper 2007), creating new and novel wetland and estuarine habitat. Recent work found that coastal meta-nurseries can be critical estuarine habitat for juvenile salmon, acting as linkages between freshwater and marine systems (Munsch et al. 2025). While salmon can be found in neighboring freshwater sloughs (Bryant 1991, Lang et al. 2006), it is unclear how important estuarine beaver dams in the CRD are for the survival and dispersal of juvenile salmon.

Coastal wetlands are highly vulnerable to sea level rise, storm surge flooding, and erosion of critical habitat (Thorne et al. 2018). While freshwater sediment inputs are important source material for deltaic rebuilding and expansion, recent work found that typical rates of watershed sedimentation are insufficient to offset increasing rises in sea level (Ensign et al. 2023). However, it is likely that some biological processes, like beaver dams, can offset and increase the capture of sediments that help elevate and stabilize low-lying salt marshes (Puttock et al. 2018). Further, estuarine beaver dams also likely protect coastal sloughs from accelerated erosional downcutting after seismic uplift and knick-pointing from diurnal tidal action.

 

To determine the influence of coastal beaver dams on salmonid habitat and sedimentation, we will use an array of methods to assess how these biological features are affecting deltaic processes. Samples will be collected at two estuarine beaver dams along the coastal margin and findings will be compared with an adjacent set of sediment accumulation transects to be collected by project collaborators. Site locations in the western CRD (Fig. 1) were selected to capture differences between areas with more marine-derived sediments (Center Slough; Fig. 2) and greater riverine deposition from the silt-laden mainstem Copper River (Central Delta; Fig. 3).

First, we will collect paired sediment cores from beaver dam impounded sloughs to determine sedimentation. We will use a gouge auger to extract a 1-m long, 2.5-cm diameter sediment core approximately 5 m behind a beaver dam to avoid outflow disturbance and store cores in cut PVC pipes. In the lab, cores will be sectioned into horizontal segments (1-cm intervals between 0-30 cm; 2-cm intervals below 30 cm) and scanned using x-ray computed tomography (CT) imaging to identify sediment stratigraphy and estimate downcore densities. Cores will also be measured by  ray spectroscopy for short-lived radioisotopes (excess ²¹⁰Pb and ¹³⁷Cs), allowing us to date the last approximate century (Peck et al. 2020). We also anticipate using historic volcanic ash layers deposited from regional Mt. Katmai (1912) and Mt. Spurr (1953, 1992) eruptions to help date sediment core stratigraphy (Wilcox 1959). We will compare beaver dam core stratigraphy to an adjacent transect of cores across the tidal saline wetlands to be collected by project collaborator Dr. Erin Peck (University of Rhode Island). CT imagery and short-lived radioisotopes will also be measured in these cores to reconstruct geomorphic change on the coastal delta. Specifically, by comparing sediment cores and detecting shifts in sediment layers after the 1964 seismic event benchmark, we hope to identify when beavers moved into these tidal sloughs, how dam construction altered relative juvenile salmonid habitat use, and determine the difference in beaver dam sediment accumulation rates on the coastal margin.

Second, we will collect water and sediment samples from beaver dam impounded sloughs to detect salmonid use of these estuarine habitats. We will use a portable water pump filter to collect aquatic environmental DNA (eDNA) of salmonid species from target beaver ponds and to detect relatively recent use of habitat (Harings et al. 2024). Water quality (temperature, salinity, conductivity, TDS and pH) and physical measurements (pond depth, height, width) will be collected at each site. In addition, we will collect sediment cores to detect historically deposited eDNA by salmonid species. We will use a gouge auger to extract an eDNA sediment core adjacent to the previous collected set. In the lab, sediment cores will be sliced (using the aforementioned methods) to preserve relative temporal stratification of eDNA accumulation (Lopez et al. 2023). Samples will be processed for eDNA extraction and salmonid community metabarcoding (Valentini et al. 2016). We will also use species-specific quantitative PCR (qPCR) for sockeye salmon (Oncorhynchus nerka), the most critically important CRD salmonid species, to determine relative abundance (Boivin-Delisle et al. 2021). From these sediment eDNA extractions, we hope to reconstruct the history of juvenile salmonid use of novel coastal beaver ponds in relation to the 1964 tectonic uplift. By investigating the life history and spatial dispersal of juvenile salmonids in the CRD estuary, we can improve our understanding of the biotic linkages between synergistic freshwater and marine systems for critically important allochthonous species.

1. EPSCoR Interface of Change (IOC) Goals: This project will be used to initiate new collaborative partnerships with local researchers at the Native Village of Eyak (NVE) and community non-profit Copper River Watershed Project (CRWP) in Cordova, ÎçÒ¹AV. This work will investigate the resiliency of juvenile salmon, which are a crucial economic resource for coastal communities in the Gulf of ÎçÒ¹AV, and how they utilize novel estuarine habitats (IOC Goal 1). The findings from this project will generate new environmental data and improve our understanding of the life history of a critically important coastal resource (IOC Goal 2).

1. Outputs: This project is an example of community-led research. We anticipate working with the community of Cordova and communicating our findings to researchers, tribal members, and community stakeholders. Projected outputs and deliverables include: (1) community presentations hosted by the NVE and CRWP; (2) presentation of findings at the 2026 EPSCoR all-hands meeting; and (3) a proposal for future community-led research on salmon use of beaver- constructed estuarine habitats in the CRD that align with the long-term goals of the NVE and regional wildlife managers.
2. Continuation of Research Support: The collaborative team plans to apply for further federal funding to continue investigation of our initial research question. Specifically, we plan to expand these findings and methodology to compare salmonid usage along transects of estuarine beaver- modified drainages as well as across the spatial salinity gradient of the coastal deltaic margin. By investigating these novel beaver-modified habitats, we hope to improve our understanding of freshwater terrestrial-marine aquatic linkages and juvenile salmonid dispersal in a critically important and dynamic coastal ecosystem.