Basis for Former Listing
The hickorynut was historically found in the Minnesota and St. Croix rivers and the Mississippi River below St. Anthony Falls (van der Schalie and van der Schalie 1950), but it is now absent from the Minnesota River (Bright et al. 1990), rare in the St. Croix River (Doolittle 1988; Hornbach et al. 1995), and uncommon and scattered in the Mississippi River (Heath 1989). The range and abundance of this species and its host fish species have been reduced. For these reasons, the hickorynut was listed as a special concern species in Minnesota in 1996.
Basis for Delisting
The Minnesota DNR initiated a ten-year statewide mussel survey in 1999 which resulted in a better understanding of the current status and distribution of the hickorynut in Minnesota. Obovaria olivaria is common and widespread within the St. Croix River drainage. The Mississippi River from St. Anthony Falls down to Lake Pepin also supports a healthy population of hickorynut, which is attributed to improvements in water quality (Minnesota Department of Natural Resources 2012). The hickorynut could potentially be successfully reintroduced to the Minnesota River drainage if the habitat conditions and water quality improve. Because of the status of the current populations and the expansion of the distribution of the hickorynut, special concern status is no longer be necessary. The hickorynut was delisted in 2013.