Modeling distributions of native Western Pearlshell and Western Ridged Mussels in the Willamette River Basin, western Oregon

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Native freshwater mussels play a vital role in keeping rivers healthy by improving water quality and supporting the broader river ecosystem. Across the Pacific Northwest (PNW), there are concerns about the status of native freshwater mussels. This is particularly true in the Willamette River Basin, where rivers are heavily altered and regulated. These modifications provide critical services to local communities, such as protection from flooding, but they have also degraded the habitat and fish populations that native freshwater mussels need to complete their life cycles.

Over the past 15 years, multiple agencies across the PNW have gathered different types of mussel presence data on two culturally and ecologically important mussel species, the Western Pearlshell Mussel - Margaritifera falcata- and the Western Ridged Mussel - Gonidea angulata. Together, these data could provide powerful insights, but differences in data collection and processing techniques have made it challenging to develop a unified approach for evaluating the status of these species. To address this, the U.S. Geological Survey is working with Tribal, federal, state, and non-profit partners to develop a modeling approach that brings mussel presence data from several distinct survey methods  together with river habitat data to predict where native Western Pearlshell and Western Ridged mussels may be found in the Willamette River Basin today and in the future.

This looks like:

1. Curating a comprehensive collection of mussel presence data for the Willamette River Basin. Data originate from surveys conducted by the US Fish and Wildlife Service, US Bureau of Land Management, US Forest Service, Oregon Department of Fish and Wildlife, Tualatin Watershed Council, the Xerces Society, and others.  Data were collected using traditional visual surveys, like snorkeling, and eDNA processed with different laboratory techniques. 

    

2. Building physical datasets to describe river habitats across the Willamette Basin. Datasets include streamflow, water temperature, and streambed sediment conditions – metrics capturing key river habitat conditions thought to influence where mussels are found. These river habitat conditions are shaped by river regulation and land management as well as natural differences across the Willamette Basin. Other datasets include barriers to fish passage up and down streams – such as dams, culverts, and waterfalls.   Because freshwater mussels are dependent upon fish to complete their life cycles, these barriers can limit mussel distributions as well.  

    

3. Building a statistical model of freshwater mussel presence in the Willamette River Basin.  The model will bring a variety of biological datasets - mussel presence - together with physical data - river habitat – in a novel way that accounts for differences in the biological datasets and places model predictions of mussel presence within the context of river management and regulation. In this way, our modeling approach facilitates decision making and the balance of human and ecosystem water needs in the Willamette River Basin. 

Program information

This research is funded by the USGS Water Mission Area EcoFlows program and leverages resources and data provided by the Willamette River Basin Integrated Water Availability Assessment (IWAAs).