Minnesota Statewide Mussel Survey

Project purpose (summary)

The primary goal of this project is to build the information base necessary to sustain freshwater mussels in Minnesota for future generations by taking inventory of these natural assets. Documenting the mussel resources of our state's rivers and streams will allow us to better measure our successes and failures in avoiding the decimation of the mussel fauna that has plagued much of North America. While mussels are valuable indicators of the health of our waterways, we know the status of mussels in relatively few of Minnesota's waterways. Of the approximately 80 river systems in Minnesota about 68 of these have not been surveyed, and portions of 6 others were only partially surveyed prior to this project.

To accomplish this project, freshwater mussels will be surveyed in threatened or under-surveyed rivers statewide. Data collected will be managed in the DNR's Natural Heritage Information System (NHIS) and will be used to plan for the conservation of mussel species in Minnesota. These data will also be used to develop educational materials for public audiences, measure the success of watershed management projects, and to assign legal conservation status to vulnerable mussel species. Data from the NHIS are widely used by landowners, public agencies, and consultants to evaluate project designs and environmental impacts. Data are provided to users upon request in printed or electronic formats and are compatible with Geographic Information Systems. A request form for Natural Heritage Information System data is available on the Minnesota DNR's Web Page at www.dnr.state.mn.us. Vouchers of collected mussel shells will be placed in the University of Minnesota's Bell Museum of Natural History and will become a part of their statewide mussel database.

Background information

Freshwater mussels, commonly called clams, occur throughout the world, but reach their greatest diversity in North America, where about 300 species are found. Unfortunately, within the last 100 years mussel communities have declined in abundance and diversity due to dam construction, stream channelization, water pollution and sedimentation, over harvesting, and the recent introduction of the exotic zebra mussel (Dreissena polymorpha). In response, groups such as the American Fisheries Society and The Nature Conservancy have identified mussels as the most imperiled group of animals in North America. Minnesota's mussel fauna is not exempt from this dilemma; 26 of the state's 49 species are now listed as either extirpated, endangered, threatened, or of special concern.

Freshwater mussels are important components of aquatic ecosystems and are increasingly being regarded as the aquatic "canaries in the coal mine". They provide food for fish, birds, and mammals, and are considered to be biological indicators of a river's health. Mussels have evolved a unique parasitic reproductive strategy that primarily involves the use of fishes as hosts for their larval stage. This relationship allows mussels to disperse wherever their host fish lives or swims to. However, unlike their host fishes, mussels do not have the ability to rapidly move away from, or avoid disturbances. Mussels are primarily sedentary in nature and often spend their entire life in a small area of the stream bed, filtering food and oxygen from the water. Consequently, they are vulnerable to disturbances to their habitats and in need of our protection.

Mussels themselves have a long history of connection to human economies. Native American Indians used mussels as a food source, and also carved their shells into utensils, jewelry, and effigies. In their quest for pearls, early settlers harvested mussels at rates that decimated many local populations. By the late 1800's and early 1900's mussel shells were again harvested, and supplied the nation with the principal material for the manufacturing of pearl buttons. Today, North American mussel shells are prized as the material of choice for seeding oysters grown in Asia for the cultured pearl industry.


Rivers to be surveyed for mussels are identified by compiling all recent and historical mussel survey information. Poorly surveyed streams are compared with the historical range of rare mussel species to identify streams with a high probability of supporting these species. Identification of priority streams also reflects the existence of threats to the stream's health and historical mussel abundance.

Priority streams are surveyed by field crews using a three-step survey protocol. First, field crews obtain useful information about the stream from other sources (e.g., fisheries stream surveys, past mussel surveys, soils and surficial geology maps) and conduct a reconnaissance of the stream to identify access points. Second, the crew conducts qualitative surveys at selected sites; collecting mussels by either wading, snorkeling, or scuba diving to obtain data on species composition and general abundance of mussel populations at these sites. Finally, the crew conducts quantitative surveys at a subset of sites with high mussel density by collecting all mussels within a timed search period, or within random 1/4 meter2 quadrats. Quantitative surveys will provide data on mussel density or abundance, species diversity, and size structure within a species (an indicator of reproductive success) for these sites.


Two survey crews began work on July 28, 1999 and field work ended on October 5, 1999. During this period 282 sites on 9 rivers and 34 tributary streams were sampled.

Status of mussel surveys on Minnesota streams, 1999

Early August survey work in the St. Croix River basin focused on completion of the Ann, Groundhouse, and Snake Rivers. High water conditions during August forced crews to move from the St. Croix River basin to the south central, southwest, and northwest areas of the state. Surveys of the Upper Iowa River system, Cedar River system, and Des Moines River system were completed during the fall, and survey work on the Roseau River was nearly completed. Sampling was initiated in 1999 on several tributaries of the Minnesota River and will continue in 2000. Survey work was also completed in the Missouri River basin where a mussel species new to Minnesota records was found alive, pondmussel (Ligumia subrostrata). Empty shells of this species were also collected from Perch Creek, a tributary of the Watonwan River (Minnesota River basin). This is significant because this species has never been reported from the Mississippi River drainage upstream of central Iowa.

Historical and current mussel species richness in selected Minnesota streams

The mussel fauna of the Snake River was the most diverse of the rivers sampled in 1999. Crews collected 24 mussel species, including 4 threatened species and 5 species of special concern in Minnesota. Surveys revealed that rivers in the southern one-third of the state no longer support their historical assemblage of mussel species. The most notable exceptions included Otter and Rose Creeks (tributaries of the Cedar River in Mower County) and portions of the Upper Iowa River. In Otter Creek, eleven mussel species were present and unlike most of the other streams surveyed it appeared to support its historical complement of mussel species based on lack of empty shells. Mussels present included a healthy population of the state threatened ellipse (Venustachoncha ellipsiformis) and the only living specimen of the state threatened mucket (Actinonaias ligamentina) found in any of the southern rivers during 1999. Two species of Special Concern were also present. Rose Creek supports a healthy population of spike (Elliptio dilatata), a special concern species that has declined in most of the state and is now abundant only in the St. Croix River basin. The Upper Iowa River supported ten live species including the state threatened V. ellipsiformis and a population of elktoe (Alasmidonta marginata), a species that is extremely rare in the southern one-third of the state.


Funding for this project was approved by the Minnesota Legislature, 1999 Minnesota Laws, Ch. 23, Sec. 16, Subd15(a), as recommended by the Legislative Commission on Minnesota Resources from the Minnesota Environment and Natural Resources Trust Fund.

Project started in July 1999. $200,000 the first year and $200,000 the second year are from the trust fund to the commissioner of the DNR for the first biennium of a three-biennium project to survey mussels statewide.


Picture of the cover for the Field Guide

Field Guide to the Freshwater Mussels of Minnesota
A tool for anyone interested in identifying and learning about Minnesota freshwater mussels. Contains photographs, shell descriptions, habitat associations, and distribution maps. Also contains general information about mussels, their importance in the ecosystem, threats to their survival, collection methods and collection regulations.

"Field Guide to the Freshwater Mussels of Minnesota" - order form (222 KB) This is a PDF file. You will need Adobe Acrobat Reader to download it.
Or purchase it directly from Minnesota's Bookstore

A poster featuring Minnesota mussels is also available in print and online. See Mussels of Minnesota.


Mike Davis, Project Manager
DNR Lake City Office
1801 S Oak Street
Lake City, MN 55041
tel. (651) 345-3331
fax (651) 345-3975

Bernard Sietman, Team Leader
MN DNR Ecological Resources
500 Lafayette Road, Box 25
St. Paul, MN 55155-4025
tel. (651) 259-5139
fax (651) 296-1811