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Northwest Mussels Live Long to Tell Their Story

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Detailed Description

Few would believe the importance of freshwater mussels to scientists here in the Pacific Northwest. These little-known and often-ignored organisms may live for over a century on the bottoms of lakes, rivers, and streams. Freshwater mussels have a story to tell, and researchers have developed a way of ‘reading’ this story. USGS Aquatic Biologist Jason Dunham discusses his ongoing research on the freshwater mussels of the Pacific Northwest.




Public Domain.


[Intro Music: Scott Pemberton Trio, Little Bobby Cobalt]

[Freshwater Mussel Interview]

[Damon Runberg] Hello and welcome. This is the USGS Oregon Science Podcast for Tuesday January 5, 2010. I’m Damon Runberg.

The U.S. Geological Survey Forest and Rangeland Ecosystem Science Center, or FRESC for short, has been conducting research on freshwater mussels in the Pacific Northwest. Many of these mussels live for a long time, but because they reside on the bottoms of creeks, rivers, and lakes, there is not much information about them compared to other species in aquatic ecosystems. Current research at FRESC is beginning to take an in-depth look at freshwater mussels and their role here in the Pacific Northwest.

Now, I would like to welcome USGS Aquatic Biologist, Jason Dunham to speak about his ongoing research on freshwater mussels.

Jason, thanks for coming in today. Can you begin by telling us why you are interested in freshwater mussels?

[Jason Dunham] Because freshwater mussels are the most imperiled group of species in North America. Recent estimates suggest extinction rates of mussels are 2-5 times higher than rates for more familiar species like birds, mammals, and amphibians. Here in the Pacific Northwest we are lucky to have populations of mussels that are still widespread and very abundant in some cases, but we still know very little about them. Changes in Pacific Northwest ecosystems that may result from increasing human populations, invasive species, and climate impacts are a big concern. Mussels are also very complicated and interesting species in their own right. They have unique associations with fish and depend on fish to disperse them through rivers and lakes. Mussels are probably the longest-lived of any species in fresh waters.

[Damon Runberg] Few people are even aware that there are freshwater mussels in the Pacific Northwest. Where do most of these mussels live?

[Jason Dunham] We find mussels in a wide variety of lakes and streams across the state. For example, it is possible to find mussels in the Willamette River, including habitats within the Portland metro area. We have found them in isolated desert streams in eastern Oregon, including the Blitzen River, as well as isolated lakes in the Oregon Dunes, where mussels live in lakes with no inlet or outlet and may have been isolated for thousands of years.

[Damon Runberg] It seems like locating these mussels can be quite the challenge. How do you go about finding them?

[Jason Dunham] The best way to find mussels is to get underwater and look for them by snorkeling. If this isn't your cup of tea, you can also find mussels by looking for shells along the shorelines of lakes and rivers or by using a glass-bottomed bucket to search for them from the water's surface. Some animals, especially river otters, can leave piles of mussel shells in middens as well.

[Damon Runberg] Because freshwater mussels persist in such a wide variety of conditions, they seem like fairly resilient organisms. Is there anything that threatens these freshwater mussels?

[Jason Dunham] We have a general sense of what may threaten mussels in this region, including the usual list of human impacts stemming from land and water use, pollution, invasive species, and harvest. Less obvious is the connection between mussels and native fish. Because mussels must have a fish host to develop, their fate is tied to the fate of fish. Studies in other regions of the U.S. and Europe have shown the status of mussels is linked to all of these factors.

[Damon Runberg] What about the effects of climate change on these mussels?

[Jason Dunham] Climate change is another potential threat for these species, especially in terms of how climates will affect flow regimes in rivers and water levels in lakes. Rising sea level in some places, such as coastal dune lakes, may be a threat to local populations. Perhaps the biggest threat is our lack of understanding of freshwater mussels in the region. In comparison to species like Pacific salmon, we know next to nothing about freshwater mussels in our region.

[Damon Runberg] What is the status of freshwater mussels in the Pacific Northwest?

[Jason Dunham] Again we know little about freshwater mussel biology, and therefore cannot conclude much about their status in this region. We know mussels are widespread and locally abundant in many streams and lakes. There are few quantitative data on declines of mussels, but there are local cases where large declines have been observed. We do not have observations of increases in local populations, but then again, we are not looking.

[Damon Runberg] Since the information on hand is so limited, where do you get your data?

[Jason Dunham] In general most of our information on freshwater mussels comes from dedicated volunteers, such as the members of the Pacific Northwest Mussel Working Group, and a few scientific case studies. Unlike salmon and other aquatic species, we do not have protocols, sampling designs, or monitoring programs in place to understand the status of mussels in the Pacific Northwest.

[Damon Runberg] Since freshwater mussels live for such a long time, can they tell us anything about the environment?

[Jason Dunham] Some mussels in the Pacific Northwest are relatively short-lived, but species like the western pearlshell can live for over a century. This is really amazing when you consider they spend almost their entire lives on the bottom of a river. Think about the incredible floods and droughts that we experience in just a couple of decades. It is hard to imagine a more difficult environment to survive in, yet mussels are possibly the longest-lived species in fresh waters. Because some species live for such extended periods, it is possible to learn about the environment from studying the age distribution within different locations or patterns of growth within long-lived individuals. Mussels form annual growth rings in their shells as they grow. Is it possible to "read between these lines" to understand something about the environmental history of fresh waters? To address this question we turned to scientists specializing in analysis of tree rings for advice on how to unlock this information.

[Damon Runberg] I remember learning about counting tree rings back when I was a child. How does the tree-ring method apply to mussels?

[Jason Dunham] Analysis of tree rings has a long tradition, and we were lucky to strike up a collaboration with Dr. Bryan Black at Oregon State University to adapt these methods to freshwater mussels. Dr. Black is trained as a forest ecologist, but has been expanding his methods to other species such as marine rockfish, geoduck clams, and other species. It turns out that long-term growth chronologies of these marine species and trees provide us with incredible insights into how different species have responded to climate change. In turn, the growth histories of these long-lived species can tell us something about the environment itself.

[Damon Runberg] How is the long-term growth chronology of a single organism important in understanding the ecosystems they live in?

[Jason Dunham] This is important to understand as we consider how climate change has already started to impact marine, terrestrial, and freshwater ecosystems. Our work on freshwater mussels in particular can help to provide the only long-term information on how individuals respond to climate change. Our results are indicating that climate responses of mussels are complex - far more complex than simple models currently in place assume, in terms of predicting responses of freshwater species to climate impacts.

[Damon Runberg] What do you hope people will take away from this research on freshwater mussels?

I think the primary importance of the work that we and others are beginning in the Pacific Northwest is to create more awareness and appreciation of freshwater mussels. We have a strong cultural identity with species such as Pacific salmon here, but there are countless other species that live under water and often out of sight. When we take the time to learn more about these little-known species we find their stories are just as interesting. Each species has a unique story and role in our fresh waters. As these stories unfold, we will be more able to ensure that future generations of people in the Pacific Northwest will be able to benefit and learn from them.

[Damon Runberg] Thanks for coming in today, Jason.

[Jason Dunham] You’re welcome.

[Damon Runberg] That’s all the time we have for today’s episode. Make sure to check out our transcripts for links to more information on the mussel research going on at USGS FRESC, as well as other research at the Center. For those who subscribe through iTunes, you can access the transcripts at our website: If you have any questions or comments about the USGS Oregon Science Podcast, email us at As always, thank you all for listening. If you want to hear more about other research the USGS is doing around the country, please check out the other USGS podcasts at

Until next time, I’m Damon Runberg.

This podcast is a product of the U.S. Geological Survey, Department of the Interior.

[Outro Music: Guitar Western Blues,]

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