## Freshwater Mussels in the Columbia and Snake River Basins

The purpose of this summary is to introduce a new and potentially
informative metric for evaluating stream ecosystem health, and to better
understand an understudied component of the Pacific Northwest riverine
environments, the populations of freshwater mussels.

**Status**

Freshwater mussel populations throughout the eastern United States and
southeastern Canada have abruptly declined in the recent past (see
section entitled Causes of Decline below). This alarming loss of species
and populations has been documented in numerous studies over the past
two decades, with over 70 percent of the species considered either
imperiled or extinct (Butler, 1989; Williams et al., 1992; Neves et al.,
1997; Brim Box, 1999; Brim Box and Williams, 1999). Extinction rates for
freshwater mussels are an order of magnitude higher than expected
background levels (Nott et al., 1995). Although the current status of
western mussels is unknown, the considerable research on eastern
species' population trends (Williams et al., 1992) provides insights
into the possible status of western freshwater mussel populations.

Current knowledge of Columbia and Snake River mussel populations
(families: Margaritiferidae and Unionidae) is very sparse. Eight
recognized species (Turgeon et al., 1998) occurred in the western U.S.;
six occurred historically in the mainstem of the Columbia; and five in
the mainstem Snake River. Of the six from the Columbia, five are in the
family Unionidae: *Anodonta californiensis, A. kennerlyi, A.
nuttalliana, A. oregonensis, Gonidea angulata* and one species in the
family Margaritiferidae: *Margaritifera falcata*. Historic records
confirm that all but *A. californiensis* occurred in the Snake River.

Although a few reports (Mavros et al. 1994; Frest and Johannes, 1995)
speculate that much of the mussels' range has been lost in the Columbia
and Snake rivers, little in the way of actual basin surveys have been
conducted. To understand changes in populations, it is important to
compare historic ranges and composition to current distributions. A
historic database maintained by the U.S. Forest Service allows
researchers to obtain details of mussel occurrence in all western states
(per. com Jayne Brim Box, USFS, Logan, UT).

We know of few projects attempting to document freshwater mussel
distribution in these particular drainages. One current, ongoing,
long-term study on freshwater mussels in the Columbia basin is being
conducted by the Confederated Tribes of the Umatilla Indian Reservation
(CTUIR). This project is investigating the distribution, status, and
population structure of freshwater mussels in the Umatilla and Middle
Fork John Day rivers in an attempt to restore mussels for associated
traditional and cultural uses.

**Importance of Mussels**

Healthy populations of riverine freshwater mussels are important for
several reasons.

Mussels were important food for tribal peoples of the Columbia and Snake
rivers. Native Americans in the interior Columbia River Basin harvested
freshwater mussels for at least 10,000 years (Lyman 1984). Ethnographic
surveys of Columbia Basin tribes reported that Native Americans
collected mussels in late summer and in late winter through early spring
during salmon fishing (Spinden, 1908; Ray, 1933; Post, 1938). Tribal
harvesters collected mussels by hand but when wading was not possible
they used forked sticks (Post 1938). Mussels were prepared for
consumption by baking, broiling, steaming, and drying (Spinden, 1908;
Post, 1938). Native American use of freshwater mussels decreased during
the last 200 years, probably due to declines in mussel populations
(Chatters 1987). A Umatilla tribal elder, however, remembered his
parents trading fish for dried mussels as late as the 1930s (per. com.
Eli Quaempts, CTUIR tribal member, 1996).

Mussels are dependent on fish hosts for larval stage development (see
discussion of life cycle below) (Coker et al., 1921; Matteson, 1955;
Fuller, 1974; Oesch, 1984). Thus long-term decimation of mussel
populations would result from a substantial and sustained reduction in
fish populations, even if habitat for mussels remains favorable
(Watters, 1992; Haag and Warren, 1998). Correspondingly, mussels provide
one path by which declines in fish taxa have propagating effects into
other parts of the ecosystem. Fish species from the family Salmonidae
that are known to be hosts to Columbia and Snake river mussel larvae
include Chinook salmon (*Oncorhynchus tschawytscha*), rainbow trout (*O.
mykiss*) (Fuller, 1974), Coho (*Oncorhynchus kisutch*), cutthroat trout
(*Salmo clarkii*), and steelhead trout (*Salmo gairdneri*)(Karnat and
Milleman 1978).

Mussels are recognized to be sensitive to a variety of watershed
environmental changes (Vannote and Minshall, 1982; Williams et al.,
1992; Strayer and Ralley, 1993) and this sensitivity makes them ideal
biomonitors of the health of the system. Ways in which freshwater
mussels can reflect the stream environment include their
presence/absence, spatial distribution, population age structure, and
tissue and shell chemistry. Mussels are nearly stationary,
bottom-dwelling filter feeders, and therefore are vulnerable to
alterations of substrate character and suspended sediment concentration,
as well as magnitude of riverbed scour and deposition, and pollution
(Strayer, 1983; Layzer and Madison, 1995; Brim Box and Mossa, 1999). In
addition, the freshwater mussels shell grows by yearly growth increments
which enable the age and time of formation to be determined. Many
histological changes are preserved in the shell as growth increments,
discontinuities, or changes in shell chemistry. These organisms are
therefore an excellent archive for studying environmental changes in
watersheds.

Because mussels can be surprisingly long-lived (over 100 years for some
species including *M.* *falcata*) (Hendelberg 1961; Hastie et al.,
2000), spatial and temporal comparisons of mussel population age
structure may allow important insights into the timing and causes of
population changes for a variety of species. A population decline of
host fish, for example, without degradation of habitat would result in
healthy mussel beds with a relative preponderance of old individuals,
whereas habitat degradation would be more likely to decimate populations
of all age groups.

Freshwater mussels are often the dominant consumer biomass within
streams. As filter feeding grazers, mussels can remove large amounts of
particulate matter from the water column and transfer those resources to
the substrate as biodeposits (agglutinated mussel feces and
pseudofeces). Mussel biodeposits are a nutrient rich and easily
assimilated food source and therefore may have significant trophic
relevance in the benthic community structure. By converting and
transferring food resources in the river system, mussels may provide
indirect links among trophic levels, reflected in alterations in
macroinvertebrate community structure.

# Causes of Decline 

Although research on freshwater mussels in this region is sparse, much
research has been conducted on the declining mussel populations of the
eastern United States. These previous studies illuminate some of the
possible causes of changes to mussel populations and demonstrates that,
even given the importance of fish populations to mussel health, habitat
changes are a very important control on mussel systems (Fuller 1974;
Bogan, 1993; Williams et al., 1992; Williams and Fuller, 1992).
Population declines are attributed to habitat degradation including
direct changes to river channels such as damming, dredging, pollution,
and harvesting mussels for commercial use (currently as cultures for the
Japanese pearl industry), and indirect changes resulting from land use
activities within the terrestrial environment (agricultural activities,
logging, urbanization, road construction) (Bogan, 1993;Williams and
Fuller, 1992; Williams et al., 1992; Butler, 1993).

In general, four types of environmental factors can affect the structure
of freshwater mussel communities: distribution and availability of host
fishes (Watters, 1992; Vaughn, 1997; Haag and Warren, 1998);
micro-habitat variables such as substrate composition and shear stress
(Layzer and Madison, 1995; Morris and Corkum, 1996; Hamilton et al.,
1997; Di Maio and Corkum, 1997; Howard and Cuffey, 2003); larger scale
drainage basin characteristics such as stream area, contamination
(pollutants), and impoundment locations (Watters, 1992; Strayer, 1993;
Frazier et al., 1996; Vaughn and Taylor, 1999); and distribution and
abundance of exotic competitive species like Asian clams (Fuller and
Imlay, 1976; Gardner, et al., 1976; Cooper and Johnson, 1980) zebra
mussels (Ricciardi et al., 1998; Schneider et al., 1998). Although a
problem in the eastern U.S., to date, zebra mussels are not established
in any western streams.

**Conclusion**

Mussel population inventories in these basins are needed to assess the
current status of freshwater mussels and to provide benchmarks from
which future changes in mussel population health and age distribution
can be inferred. This understanding will assist designs for meaningful
monitoring programs for these populations, will contribute to
interpretations of population changes, and may ultimately prove
important in efforts to preserve these organisms in northwestern
streams. Additionally, by recognizing mussels as a new and potentially
informative metric, methods for evaluating stream ecosystem health will
be improved.

**Freshwater Mussel Life History**

Understanding specific pathways by which environmental variables may
affect mussel populations requires understanding the life cycle of these
organisms. Therefore a brief review of the life cycle follows.

Sperm are released to the water and entrained by the inhalant siphon of
females (Oesch, 1984; Cummings, 1992; Amyot and Downing, 1998), after
which fertilization occurs in the suprabranchial chambers of the female
(Cummings, 1992). Therefore, reproductive success is associated with the
spatial aggregation of populations. Complete fertilization failure has
been shown to occur when local density dropped to less than 10 mussels
per square meter (Amyot and Downing, 1998).

The fertilized ova are incubated and develop into minute bivalved larval
stage called glochidia (Fuller, 1974; Oesch, 1984; Butler, 1993), which
are stored in the females\' gills (Oesch, 1984). In spring or summer,
glochidia are expelled to begin the parasitic phase of their life cycle.
The odds against survival are greatest during the weeks immediately
following the discharge of the glochidia (Oesch, 1984). Glochidia cannot
swim, but can only drift in water currents where they must come into
contact with the gills or fins of an appropriate host fish. During this
time, the glochidia are vulnerable to predation. If an appropriate fish
host is encountered, glochidia must then successfully parasitize the
fish to undergo metamorphosis (Oesch, 1984) into the adult mussel form.
To increase the likelihood that glochidia will contact host fishes, some
mussel species expel glochidia resembling fish food such as worms,
insect larvae or minnows (Butler, 1993).

The duration of the parasitic stage varies from 5 to 120 days (Fuller,
1974; Oesch, 1984; Williams et al., 1992; Butler, 1993), primarily as a
function of water temperature (higher temperatures causing shorter
durations) (Nystrom et al., 1996). After metamorphosis, the mussels
emerge from the fish tissue and begin an independent life on the bed of
the stream. Juvenile mussels must fall to substrate suitable for their
adult life requirements or they will not survive. Suitable substrates
have been documented as firm but yielding and stable (Negus, 1966;
Fuller, 1974). In general, shifting sands, and suspended fine muds,
clays, and silt are noted as harmful to both juvenile and mature mussels
(Fuller, 1974; Williams et al., 1992).

Mussels orient themselves on the bottom of a stream with their anterior
ends buried in the substrate, usually with the two valves slightly open,
permitting the intake of food and oxygen while allowing waste materials
to leave the body (Oesch, 1984). Food consists of organic detritus,
algae, and diatoms (Coker et al., 1921; Matteson, 1955; Fuller, 1974;
Burky, 1983). Increases in fine sediment, whether deposited or
suspended, may impact mussels by interfering with feeding and/or
respiration (Fuller, 1974; Robinson et al., 1984; Brim Box 1999; Brim
Box and Mossa, 1999).

Most mussels travel in response to abnormal or transient ecological
events. For example, a drop in water level that exposes the mussel to
air is motivation for some species to seek deeper water (Coker et al.,
1921; Oesch, 1984). Often, in late summer, mussel trails are visible as
the water recedes. However, glochidia parasitized fish swimming from one
place to the next accomplishes most movement.

## References

Amyot, J.P., Downing, J.A. Locamotion in Elliptio complanata
(Mollusca:Unionidae): A reproductive function? Freshwater Biology 39:
351-358.

Bogan, A. 1993. Freshwater bivalve extinctions (Mollusca: Unionoida): A
search for causes. American Zoology 33:599-609.

Brim Box, Jayne, 1999. Community Structure of Freshwater Mussels
(Bivalvia: Unionidae) in Coastal Plain Streams of the Southeastern
United States. Dissertation, Department of Fisheries, University of
Florida, Gainesville, 1999.

Brim Box, J. and Mossa, J., 1999. Sediment, land use and freshwater
mussels: prospects and problems. Journal of the North American
Benthological Society 18(1): 99-117.

Brim Box, J. and Williams, J.D., 1999. Unionid mollusks of the
Apalachicola Basin in Alabama, Florida and Georgia. Bulletin of the
Alabama Museum of Natural History, 21: 1-156.

Burky, Albert J., 1983. Physiological ecology of freshwater bivalves. In
The Mollusca, eds. W.D. Russell-Hunter, pp. 281-327. Orlando, Florida:
Academic Press Inc.

Butler, R.S., 1989. Distributional records of freshwater mussels
(Bivalvia: Unionidae) in Florida and south Alabama with zoogeographic
and taxonomic notes. Walkerana 3: 239-261.

Butler, R. 1993. Results of a status survey for eight freshwater mussels
(Bivalvia: Unionidae) endemic to eastern Gulf slope drainages of the
Apalachicolan region of southeast Alabama, southwest Georgia, and north
Florida, U.S. Fish and Wildlife Service, Jacksonville, Florida.

Chatters, J.C. 1995. Population growth, climatic cooling, and the
development of collector strategies on the Southern Plateau, Western
North America. Journal of World Prehistory 9: 341-400.

Coker, R.E., Shira, A.F, Clark, H.W., and Howard, A.D., 1921. Natural
History and Propagation of Freshwater Mussels. Bulletin of the Bureau of
Fisheries 37:1-29.

Cooper, C.M., and V.W. Johnson 1980. Bivalve mollusca of the Yalobusha
River, Mississippi. The Nautilus 94:22-24.

Cummings, Kevins S. and Mayer, Christine A., 1992. Field Guide to
Freshwater Mussels of the Midwest. Champaign, Illinois: Illinois Natural
History Survey.

Di Maio, J., and L.D. Corkum, 1997. Patterns of orientation in unionids
as a function of rivers with differing hydrological variability. Journal
of Molluscan Studies 63: 531-539.

Doppelt, B., Scurlock, M., Frissell, C., Karr, J. 1993. Entering the
Watershed. Washington, D.C.:Island Press.

Frazier, B.E., T.J. Naimo, M.B. Sandheinrich. 1996. Temporal and
vertical distribution of total ammonia nitrogen and un-ionized ammonia
nitrogen in sediment pore water from the Upper Mississippi River.
Environmental Toxicology and Chemistry 15: 92-99.

Frest, T. J., and E. J. Johannes. 1995. Interior Columbia Basin mollusk
species of special concern. Final Report to Interior Columbia Basin
Ecosystem Management Project. Deixis Consultants, Seattle, WA.

Fuller, S. 1974. Clams and mussels (Mollusca: Bivalvia). In Pollution
Ecology of Freshwater Invertebrates, eds C.W. Hart Jr., and S L H.
Fuller, pp.215-273. New York: Academic Press.

Fuller, S.L.H., and M.J. Imlay 1976. Spatial competition between
Corbicula manilensis (Philippi), the Chinese clam (Corbiculidae), and
fresh-water mussels (Unionidae) in the Waccamaw River Basin of the
Carolinas (Mollusca: Bivalvia). Ass. Southeast. Biol. Bull 23:60.

Gardner, J.A., Jr., W.R. Woodall, Jr., A.A. Staats, Jr., and J.F. Napoli
1976. The invasion of the Asiatic clam (Corbicula manilensis Phillippi)
in the Althamaha River, Georgia. The Nautilus 90:117-125.

Haag, W.R., and M.L. Warren, 1998. Role of ecological factors and
reproductive strategies in structuring freshwater mussel communities.
Canadian Journal of Fisheries and Aquatic Sciences 55: 297-306.

Hamilton, H., J.B. Box and R.M. Dorazio, 1997. Effects of habitat
suitability on the survival of relocated freshwater mussels. Regulated
Rivers-Research & Management 13(6): 537-541.

Hastie H.C., M.R. Young, P.J. Boon, 2000. Growth characteristics of
freshwater pearl mussels, *Margaritifera margaritifera.* Freshwater
Biology 43: 243-256.

Hendelberg, J. 1961. The freshwater pearl mussel *Margaritifera
margaritifera.* Journal of Conchology 29:207-218.

Howard, J. K., and K. Cuffey. 2002. Freshwater mussels in a California
North Coast Range river: occurrence, distribution, and controls. Journal
of the North American Benthological Society 22(1): 63--77.

Karnat, D.W., and R.E. Milleman. 1978. Glochidiosis of salmonid fishes.
Comparative susceptibility to natural infection with *Margaritifera
margaritifera* and associated histopathology. Journal of Parasitology
64(3): 528-537.

Layzer, J., and Madison, L. 1995. Microhabitat use by freshwater mussels
and recommendations for determining their instream flow needs. Regulated
Rivers: Research & Management 10:329-345.

Lyman, R.L. 1984. A model of Large Freshwater Clam Exploitation in the
Prehistoric Southern Columbia Plateau Culture Area. Northwest
Anthropological Research Notes 18: 97-107.

Matteson, M.R., 1955. Studies on the natural history of the Unionidae.
American Midland Naturalist 53(1): 126-145.

Mavros, W.V., D.A. Neitzel, G.A. Martenson, T.J. Frest, E.J. Johannes,
1994. Mollusc survey of the Lower Granite Reservoir. Prepared for the
Department of the Army, Walla Walla District, Corps of Engineers.

Morris, T.J. and L.D. Corkum, 1996. Assemblage structure of freshwater
mussels (Bivalvia: Unionidae) in rivers with grassy and forested
riparian zones. Journal of the North American Benthological Society,
15(4):576-586.

Negus, C.L., 1966. A quantitative study of growth and production of
unionid mussels in the river Thames at Reading. Journal of Animal
Ecology 35:513-532.

Neves, R.J., A.E. Bogan, J.D. Williams, S. A. Ahlstedt, and P.W.
Hartfield, 1997. Status of aquatic mollukes in the southeastern United
States: a downward spiral of diversity. Pages 44-86 in G.W. Benz and
D.E. Collins (eds.) Aquatic fauna in peril: the southeastern
perspective. Special Publication 1, Southeast Aquatic Research
Institute. Decatur, Georgia: Lenz Design and Communications.

Nott, M.P, E. Rogers and S. Pimm, 1995. Modern extinctions in the
kilo-death range. Current Biology 5: 14-17.

Nystrom, J., E. Dunca, H. Mutvei, and U. Lindh, 1996. Environmental
history as reflected by freshwater pearl mussels in the River Vramsan,
southern Sweden. Ambio 25: 350-355.

Oesch, Ronald D. 1984. Missouri Naiades; A Guide to the Mussels of
Missouri. Jefferson City, Missouri: Missouri Department of Conservation.

Post, R.H. 1938. The Subsistence Quest. In the Sinkaietk or Southern
Okanogan of Washington. edited by L. Spier. General Series in
Anthropology 6: 9-34.

Ray, V.F. 1933. The Sanpoil and Nespelem: Salishan Peoples of
Northeastern Washington. University of Washington Publications in
Anthropology. Vol. 5.

Ricciardi, A., R.J. Neves, J.B. Rasmussen, 1998. Impending extinctions
of North American freshwater mussels (Unionoida) following the zebra
mussel invasion. Journal of Animal Ecology, 67(4): 613-619.

Robinson, W.E., W.E. Wehling, and M.P. Morse, 1984. The effect of
suspended clay on feeding and digestive efficiency of the surf clam,
Spisula solidissima. Journal of Experimental Marine Biology and Ecology
74:1-12.

Schneider, D.W., C.D. Ellis and K.S. Cummings, 1998. A transportation
model assessment of the risk to native mussel communities from zebra
mussel spread. Conservation Biology, 12(4): 788-800.

Spinden, H. J. 1908. The Nez Perce Indians. Memoirs of the American
Anthropological Association. 2(3): 167-274.

Strayer, D., 1983. The effects of surface geology and stream size on
freshwater mussel distribution in southeastern Michigan, USA. Freshwater
Biology 13: 253-264.

Strayer, D., and Ralley, J. 1993. Microhabitat use by an assemblage of
stream-dwelling unionaceans (Bivalvia), including two rare species of
Alasmidonta. American Benthological Society 12(3):247-258.

Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G.
Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G.
Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J.
D. Williams. 1998. Common and scientific names of aquatic invertebrates
from the United States and Canada: mollusks, 2nd edition. American
Fisheries Society, Special Publication 26, Bethesda, Maryland. 509 pp.

Vannote, R., and Minshall, G. 1982. Fluvial processes and local
lithology controlling abundance, structure, and composition of mussel
beds, Proceedings of the National Academy of Sciences 79:4103-4107.

Vaughn, C.C., 1997. Regional patterns of mussel species distributions in
North American rivers. Ecography 20(2): 107-115.

Vaughn, C.C. and C.M. Taylor, 1999. Impoundments and the decline of
freshwater mussels: A case study of an extinction gradient. Conservation
Biology 13:912-920.

Watters, G.T., 1992. Unionids, fishes, and the species area curve.
Journal of Biogeography 19: 481-490.

Williams, J., and Fuller, S. 1992. Effects of impoundments on freshwater
mussels (Mollusca: Bivalvia: Unionidae) in the main channel of the Black
Warrior and Tombigbee Rivers in Western Alabama. Alabama Museum of
Natural History Bulletin no. 13.

Williams, J., Warren, M.; Cummings, K., Harris, J., and Neves, R. 1992.
Conservation status of freshwater mussels of the United States and
Canada. Fisheries 18(9): 6-22.