Freshwater clams, also referred to as unionid mussels, are the most endangered group of animals in North American waters. North America has the most species of any continent in the world. However, of the 297 known native species, 213 are considered endangered, threatened, or of special concern. Their populations appear to be declining due to habitat alterations, increased pollution, poor water quality, and invasions by exotic species such as zebra and quagga mussels which out-compete the native mussels.
An extensive study of the native unionid mussels was completed at the Lakeshore in 2003. Twelve waterbodies were sampled for both native and exotic mussels and the native mussels were identified and aged. The good news is that 16 species of native clams were found and that there did not appear to be any pollution factors impacting the various mussel species. The researchers also found that individuals of some of the species were over 20 years old! The bad news is that zebra mussels were found in 6 of the 12 waterbodies surveyed and their numbers increased just during the 4 year survey period. Hundreds of zebra mussels could be found attached to the native mussel shells, to submerged rocks, and even to dragonfly larvae. Scientists continue to search for a treatment that will remove or reduce this very unwanted guest and not impact the native mussels.