NATIVE UNIONOIDS OF THE UPPER MISSISSIPPI RIVER SYSTEM:  HOW DOES THE
MISSISSIPPI RIVER FIT IN THE PICTURE? 

Marian E. Havlik1 and Jennifer S. Sauer2.   
1Malacological Consultants, La Crosse, WI 54601-4969  2U.S. Geological Survey, Upper
Midwest Environmental Sciences Center, La Crosse, WI 54603.

Historically, at least 51 of 304 native freshwater mussel species (Order Unionoida) in the United
States have been documented in the Upper Mississippi River System (UMRS = Upper
Mississippi and Illinois Rivers).   Two unionoids are federally endangered, and a third is under
federal review.  Although 28 species have some type of special status designation in the five
states that border the UMRS, 44 species have been documented in UMRS surveys conducted
since 1968.  The loss of UMRS species richness may be linked to habitat changes after the locks
and dams were built.  Nearly all of the seven species not found recently were considered
infrequent inhabitants of the UMRS mainstem by late 19th and early 20th century biologists,
since they were more commonly found in UMRS tributaries where they all still survive.  Havlik
and Sauer (2000) give the present status of all 51 species historically found in the UMRS.  The
conservation status varies from state to state, because each state describes the status of a species
population within that particular state, not the UMRS as a whole.   Leptodea leptodon and
Alasmidonta viridis have been found in UMRS tributaries, but rarely in the UMRS.   Some
species reported in the early literature were apparently misidentified, or vouchers do not seem to
exist.  Some rare species may go unrecognized, indicating the importance of depositing unusual
specimens in a museum and having identifications verified by an experienced malacologist.  See:
http://www.umesc.gov/reports-publications/psrs/emesc_psr.html 

Keywords:  Mississippi River mussels, unionoids, unionid surveys, unionid species, endangered
species