Freshwater mussel with host fish illustration

  Pacific Northwest Native Freshwater Mussel Workgroup

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Projects and Presentations

Distribution Map

Caged Mussel (abstract)

2003 Mussel Surveys (abstract)

Freshwater Mussels of the Owyhee River Basin-a Prehistoric Perspective (Paper abstract)

Overlooked Animals: Native Freshwater Mussels in the Greater Portland Area (Poster abstract)

Pacific Northwest Native Freshwater Mussel Workgroup (Poster abstract)

Status of Smith-Bybee Lakes Mussel Populations in 2000-2001 (Project completed in 2001)

Church Creek Mussel Survey - July 2003 Snohomish County Public Works (Poster abstract) (Poster only)

Distribution, abundance, and habitat use of freshwater mussels in four urban streams of Clark County, Washington (Project beginning in 2004)

Spatial Distribution and Habitat Use of the Western Pearlshell Mussel (Margaritifera falcata) in a Western Washington Stream (Project completed in 2003)

Distribution, abundance, and habitat use of freshwater mussels in four urban streams of Clark County, Washington.

Principal Investigators:
Sam Lohr, U.S. Fish and Wildlife Service, Jamie Glasgow, Washington Trout

U.S. Fish and Wildlife Service, Washington Trout, Friends of Ridgefield, Lower Columbia River Estuary Partnership, Washington State University, Clark College, Americorps, Clark County Watershed Stewards, and The City of Vancouver.

Metro Greenspaces funded the grant in the amount of $21,000.00.

Project Duration:
The work is scheduled to begin in June 2004 and be finished by December 2004.

This project will provide a comprehensive survey of freshwater mussels in four urban streams located in Clark County, Washington. It will be comparable to a similar project that is planned for King County, Washington in 2003. Combining these two projects will increase the scope and robustness of our results and will provide much needed information as to the effects of urbanization on the populations of freshwater mussels.
Washington Trout and the U.S. Fish and Wildlife Service, Columbia River Fisheries Program Office, will act as partners in this project and will share data collecting and data analysis responsibilities. Survey work will include traveling to designated streams, executing standardized sampling protocol that will include counting and measuring
mussels and recording habitat features such as substrate size, water velocity, and water quality. Data will be assimilated and analyzed using Geographic Information Systems technology and will be made available to public.

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Spatial Distribution and Habitat Use of the Western Pearlshell Mussel (Margaritifera falcata) in a Western Washington Stream

Principal Investigators:
Jen Stone, Scott Barndt, Michael Gangloff

Funding Source:
U. S. Fish and Wildlife Service

Project Duration:
2000 – 2002

We investigated the spatial distribution and habitat associations of western pearlshell mussels (Margaritifera falcata) in a southwest Washington stream at multiple scales using a systematic sampling design. Variation in mussel occurrence differed with the scale of the observations, being lower among study reaches and higher within reaches. Additionally, mussels exhibited a highly contagious, non-random spatial distribution pattern. The spatial distribution of mussels at large scales (across reaches) was associated with dissolved oxygen and shear stress. Mussel distribution at small scales (with the 60m reaches) was associated with wetted width, canopy, abundance of small gravel substrate, and distance from the stream bank. Mussels were found in locations having reduced shear stress, turbulence (as measured using the Reynolds number), and gradient and increased wetted width, abundance of small gravel, dissolved oxygen, and conductivity. Based on our computed habitat suitability curves, optimum water depth was 0.2 – 0.6 m and optimum current velocity was 0.23 – 0.30 m/sec. Mussels preferred substrates where boulders increased bed roughness, allowing small gravel and sand to create a stable, heterogeneous substrate. Our data provide insight as to how habitat parameters, particularly those relating to streambed stability and stream energy, affect spatial variation in mussel distribution and may be useful in designing future mussel population studies.

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Freshwater Mussels of the Owyhee River Basin—a Prehistoric Perspective (to be presented at OR AFS 2004)

Authors: Cynthia K. Tait*, Bureau of Land Management, 100 Oregon St, Vale, OR, 97918; 541-473-6246;; Allan K. Smith, Pacific Northwest Native Freshwater Mussel Workgroup, Hillsboro, OR

Abstract: Beginning in 2001, freshwater mussels have been inventoried and systematically sampled on drainages in the Owyhee River Basin, including 10 remote sites on the Owyhee River. Only one mussel species, Gonidea angulata, was encountered, but the species was widespread and multiple age-classes were present. However, mussel shells found in prehistoric Indian middens located on the main river and on a tributary included shell fragments of Margaritifera falcata as well as G. angulata, indicating that both species were present and accessible for harvest ca. 2000 years b.p. Because M. falcata relies on salmon and trout for hosts, its absence or scarcity in the Owyhee could be related to historic extirpation of anadromous salmonids and the subsequent introduction of unsuitable hosts such as nonnative smallmouth bass (Micropterus dolomieui). Declines in some European Margaritifera populations have been linked to trout host densities that drop below a critical threshold. G. angulata’s fish host preferences are unknown, although this species is likely to be less host specific than M. falcata and, therefore, less vulnerable to changes in fish assemblages.

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Overlooked Animals: Native Freshwater Mussels in the Greater Portland Area (to be presented at OR AFS 2004)

Presenter: Al Smith, Hillsboro, Oregon;

Contact: Phone: 503-628-7825, Email:

Abstract: Native freshwater mussels in the Greater Portland area receive very little attention from biologists, much less the public. Yet they are very interesting and ecologically important animals. They filter huge amounts of water over their long lives, provide food for predators such as raccoons, river otters and muskrats, are an indicator of stream health and have a fascinating life history. Three species of mussels currently occur in the area: Anodonta oregonensis (Oregon floater), A. californiensis (California floater) and A. wahlamatensis (Willametter floater). Shells have been found for two other species that likely also live here: Margaritifera falcata (western pearlshell) and Gonidea angulata (western ridgemussel). Depending on the species, they occur in the area’s rivers, streams, sloughs and lakes. Two examples, Fanno and Rock creeks, both tributaries of the Tualatin River, in the southwest and west parts, respectively, of the area support populations of A. oregonensis with juvenile mussels found in both streams. This is a good sign because it means the habitat in these somewhat degraded streams meets their survival and reproductive needs. Smith-Bybee lakes in North Portland, on the other hand, probably lost their populations of mussels in the drought of 2001. An interesting historical note is that A. oregonensis and A. wahlamatensis were first scientifically described as species by Isaac Lea in 1839 from the “Wahlamat near its confluence with the Columbia River”.

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Pacific Northwest Native Freshwater Mussel Workgroup (to be presented at OR AFS 2004)

Presenters: : Jen Stone, Al Smith

Contact: Phone: 360-696-7605, Fax: 360-696-7968, Email:

Abstract: On February 19, 2003, a workshop on freshwater mussels was held in Vancouver, Washington that consisted of presented papers, a panel discussion and discussion of future activities. The workshop was attended by 91 participants of very diverse backgrounds. Out of this meeting the Pacific Northwest Native Freshwater Mussel Workgroup was founded. The goal of the Workgroup (including eight objectives) is to ”Ensure that freshwater mussel research, management, and educational activities are coordinated, prioritized and are consistent with identified information needs”. The Workgroup is divided into two committees; an outreach and education group and a research, monitoring and management activities group. The Workgroup meets at least four times annually. Accomplishments so far are establishment of a website (website here), two mussel classes scheduled for next year in Portland and Ellensburg, Washington and the annual workshop. The workshop will be held in western Washington with the theme of a review of the status of freshwater mussel research, management and education. The annual workshop will rotate around the Northwest. The status of the seven species of freshwater mussels in the Northwest has received very little attention from biologists, let alone the public. The Workgroup intends to raise the awareness of the status of freshwater mussels and assure that the knowledge base about these mollusks continues to build.

View Poster

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Status of Smith-Bybee Lakes Mussel Populations in 2000-2001 (to be presented at OR AFS 2004)

Presenter: Al Smith

Contact: Phone: 503-628-7825, Email:

Abstract: I surveyed the shores of Smith-Bybee lakes in North Portland, Oregon five times in August and September 2000 and 2001 for freshwater mussel shells when the lakes were very low or dry from drought. I found shells from recently dead native mussels of three species: Anodonta oregonensis (Oregon floater), A. californiensis (California floater) and A. wahlamatensis (Willamette floater). The mussels were likely scavenged by birds after dying from desiccation or high temperature. I found shells from 39 individual mussels, all very large adults. The percentage species composition at Smith-Bybee lakes was nearly the same as the species composition from Prescott Slough on the Columbia River near Rainier for the same years. Prescott Slough was also very low in 2000-2001. However the mean sizes of A. oregonensis and A. californiensis were significantly larger at Smith-Bybee lakes than at Prescott Slough. In addition, the size range for both species was greater at Prescott Slough due to multiple year classes in the populations. No successful mussel reproduction has occurred at Smith-Bybee lakes for many years. The reason is unknown. Since both lakes went virtually dry in 2001, the old, declining mussel populations are likely gone. All three species depend on attachment to fish gills at the larval stage (glochidia) for nurturing, protection, growth and dispersion. The mussel populations should eventually return to the lakes as long as fish from outside the lakes have access and as long as there is perennial standing water in parts of the lakes.

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Caged Mussel

Investigator: Washington Trout

Abstract: The purpose of this study was to determine the spatial distribution, in the upper Bear Creek Watershed, of chemicals that are bioaccumulated by the freshwater mussel Margaritifera falcata. The M. falcata population of Bear Creek has declined greatly over the last 40 years; it is unknown what proportion of this decline is due to exposure to toxic chemicals from anthropogenic sources. As filter feeders, freshwater mussels have a great deal of direct contact between their body tissues and any chemicals dissolved or suspended in the water. By placing caged mussels in strategic locations throughout the Bear Creek watershed, we will be able to determine the spatial distribution of the chemicals which are being bioaccumulated by M. falcata. Cage location will be chosen to specifically examine the relationship between upstream landuse and accumulated chemicals.

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2003 Mussel Surveys

Investigator: Washingon Trout

Abstract: Western pearlshell freshwater mussels (Margaritifera falcata) inhabit Bear Creek in King County, Washington. In 2002 Washington Trout determined M. falcata bed size, density, and population age structure at a sub-sample of ten known freshwater mussel beds on Bear Creek. In 2003 five of the ten beds were resampled in order to elucidate changes in mussel bed density and population age structure. In order to make certain that population age structure estimates were accurate, a detailed search for juvenile mussels was conducted using a methodology designed explicitly for the location of smaller individuals. The results of this study provide the beginnings of a documented population trajectory for the Bear Creek mussel population. The number of live mussels sampled increased in two beds between 2002 and 2003 and decreased in three beds, indicating that the mussel population in upper Bear Creek is likely stable on a year-to-year basis. In order to make certain that population age structure estimates were accurate, a detailed search for juvenile mussels was conducted using a methodology designed explicitly for the location of smaller individuals. No live mussels < 30 mm were identified in this study, indicating a lack of detectable juvenile recruitment in Bear Creek.

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Church Creek Survey of Freshwater Mussels

Principal Investigators: Sacha Johnson, Jake Jacobson, Kathy Thornburgh

Organizations/Partners involved: Barry Dreher, citizen volunteer

Funding Source: Snohomish County Surface Water Management

Project Duration: summer 2003

Abstract: The survey was performed between July 16, 2003 and August 1, 2003 on Church Creek, a small stream running through northern Snohomish County and a tributary to the larger Stillaguamish River. Approximately 7,300 feet of stream were surveyed through a wide variety of riparian habitats such as city parks, pasture lands, and mature forests. Our objective was to develop an efficient method to obtain baseline mussel distribution and abundance information throughout a watershed using individuals with a moderate level of training and a minimum amount of equipment. We used the following equipment in our surveys: GPS, hip chain, Aquascope viewing scope, polarized glasses, field forms, clipboard, pencil, measuring rod, Ziploc bags, and hip waders. The mussel count for a stream reach five channel widths long was estimated each time a mussel was sighted. The estimated mussel count was recorded using the following classifications: 0.3 for 1-3 mussels, 1 for 4-10 mussels, 2 for 11 to 50 mussels, and 3 for more than 50 mussels. Other information recorded included stream habitat type (pool, riffle, or glide), wetted channel width, channel depth, sediment type, and GPS location of mussel sightings. Percent of dead shells was noted for each reach surveyed. The only mussel species seen during the survey was the Western pearlshell, Margartifera falcata. Using our protocol, a preliminary survey of mussel densities in a reach of about 1.5 miles of a small creek was completed by two individuals in 8-10 working days. The individuals needed no rigorous science background, only good eyesight and basic measurement skills. Our citizen volunteer, Barry Dreher, provided local knowledge about the watershed and introductions to many streamside landowners. The survey is an opportunity to involve community residents in learning about their watershed and local water issues.

See poster now.

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Field Guide to the Freshwater Mussels of the Pacific Northwest 2nd Edition

The Xerces Society for Invertebrate Conservation

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