U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet FS 2004-3037

May 2003

Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin

Development of Landscape Models for Conservation of Freshwater 

Mussels in the Upper Mississippi River Basin

Freshwater mussels are the most imperiled group of animals 

in North America. About 70% of the 300 native species are 

considered extinct, endangered, threatened, or of special 

concern. Freshwater mussels are a renewable resource, 

providing signifi cant ecological and economic benefi ts to the 

Nation. Mussels serve as a food resource for many animals; 

they improve water quality by fi ltering contaminants, 

sediments, and nutrients; and their shells are used in 

producing cultured pearls. Their declines may be a signal of 

critical problems in river ecosystems.

Although many threats may be contributing to the declines 

in species density and diversity, past efforts have not 

determined which threats are most important. Because 

freshwater mussels are declining nationwide, it is important 

to understand what contributes to their distribution (location) 

and abundance (numbers) across large geographic areas. 

Much of the research on mussels has been conducted on small 

streams by teams of mussel specialists measuring traditional 

habitat variables. Most attempts to predict the distribution or 

abundance of mussels from variables such as substrate type 

or water depth have failed when tested critically, suggesting 

that these measures are inadequate descriptors of mussel 

communities. Also, many freshwater mussels require a fi sh 

host to complete their life cycle. Therefore, management 

approaches need to maintain the connection between mussels 

and their host fi sh. Further advances in understanding 

mussel populations will probably require a multidisciplinary 

approach that includes biology, chemistry, and hydrology in 

both large and small geographic areas.

The Higgins eye (Lampsilis higginsi) is one of several freshwater mussel 

species in the Upper Mississippi River Basin on the Federal endangered 

species list.

26%

Endangered

Extinct

7%

Undetermined

5%

24% Stable

15%

Threatened

24%

Special 

Concern

Declines in the number of species and abundance of freshwater mussels have been observed in many large rivers. The Nature Conservancy 

estimates that 72% of mussel species are vulnerable to extinction or are 

already extinct.

In 2001, scientists at the Upper Midwest Environmental 

Sciences Center began to develop predictive models. These 

computer models relate the distribution of freshwater mussels 

to physical and biological variables over large and small 

geographic areas. A geographic information system (GIS) 

allows scientists to examine the relations among many 

databases and provides graphical displays of these data. We 

developed a GIS database on the distribution and abundance 

of native mussels from eight studies conducted from 1975 to 

2001. These studies were conducted in Navigation Pool 8, a 

38-km reach of the Upper Mississippi River near La Crosse, 

Wisconsin. The data from the Pool 8 studies cover 587 

locations and provide good geographic coverage throughout 

the pool, although most locations are near the deepest part 

of the channel. Of the 587 locations, roughly 60% contained 

mussels representing 37 species, including the endangered 

Higgins eye (Lampsilis higginsi). Densities of freshwater 

mussels were highly variable, ranging from 0 to 130 mussels 

per square meter.

We also assembled a database on physical and biological 

variables of Pool 8 to compare to mussel distributions. 

Physical features included land cover in the surrounding area; 

aquatic area type (e.g., main navigation channel, backwater 

lake); longitudinal position within the pool; proximity to 

wing dams, tributaries, and deep holes; and various hydraulic 
Spatial distribution of 587 locations that have been sampled for freshwater mussels in Navigation Pool 8 of the Upper Mississippi River during 

1975-2001. About 60% of these locations contained mussels (blue dots) 

and 40% did not (red dots).

variables. We are also interested in determining if certain 

biological attributes infl uence mussel distribution. We 

grouped mussels into guilds on the basis of breeding strategy, 

conservation status, commercial status, shell shape, and the 

number of different fi sh families that serve as fi sh hosts. We 

are now investigating relations among the biological and 

physical variables and building simple models to generate 

hypotheses for future research.

Recent analysis suggests that several hydraulic variables 

may be important in predicting the distribution of mussels. 

For example, mussels are most often found in areas with 

a combination of low shear stress (the force exerted by 

moving water near the river bottom) during periods of 

high fl ows and some minimum level of current velocity 

during low fl ow periods. Such areas may allow mussels to 

maintain their position during fl oods (low shear stress) and 

still provide adequate food resources, oxygen, and removal 

of waste products during low water periods. Preliminary 

analysis shows that three variables–velocity, depth, and shear 

stress–can predict the presence of mussels 80–96% of the 

time. Of the 587 locations, however, only about 50 meet the 

optimal conditions predicted by these models. We don’t know 

whether these conditions are found in unsampled locations or 

only in a very small percentage of the pool.

Certain biological attributes may also infl uence the 

distribution of mussels. For example, thin-shelled species 

were most common in the upper portion of the pool. The 

upper portion is more river-like than the lower dammed 

portion, which is more lake-like. In contrast, those 

locations dominated by thick-shelled species were evenly 

distributed throughout the pool. Mussels in the subfamily 

Anodontinae (short-lived, early maturing, rapid growth) were 

predominately found in the main navigation channel. Mussels 

in the subfamilies Lampsilinae (long-lived, late maturing, 

slow growth) and Unioninae (moderate life span, moderate 

maturity, and moderate growth) were more widely distributed 

among other aquatic areas in the pool.

Present analysis focuses on dividing the 587 locations into 

those with and without juveniles and those with low and 

high mussel densities. Initially, we will use classifi cation and 

regression techniques to categorize mussels into groups with 

similar physical and biological characteristics. We will then 

develop more detailed analytical models using those variables 

that seem to infl uence the distribution of mussels.

We conducted the study using Navigation Pool 8 because 

the USGS-administered Long Term Resource Monitoring 

Program provides 15 years of data about physical features 

(velocity models, depths) and biological components 

(fi sh, invertebrates, plants). However, this type of analysis 

could be done in other data-rich locations at large and 

small geographic scales and should be broadly applicable 

throughout other areas such as the Great Lakes region.

See the project Web page for more information. http:

//www.umesc.er.usgs.gov/aquatic/native_mussels/

5004455.html

For more information, contact Teresa Newton

Upper Midwest Environmental Sciences Center

2630 Fanta Reed Road, 

La Crosse, WI 54603

Phone: 608.783.6217

Email: tnewton@usgs.gov

http://www.umesc.usgs.gov/