Status of the snuffbox mussel Epioblasma triquetra (Rafinesque) in Illinois: a functionally extirpated species

Within Illinois, the state-endangered snuffbox mussel Epioblasma triquetra (Rafinesque) is currently found only in a small stretch of the Embarras River in Douglas and Coles counties and is considered one of the rarest freshwater mussels in the state. To assess the current population status of E. triquetra in Illinois, I estimated density, length frequency, and sex ratio of the Embarras River population. I also examined the status of the snuffbox mussel’s host fish, the logperch Percina caprodes (Rafinesque), to determine if the fish was present in this area. Seven sites in the Embarras River were sampled for freshwater mussels and fishes during the summers of 2007 and 2008 using common sampling proto-cols. Only five adult (55 mm) E. triquetra males were collected from two sites, sug-gesting this species is functionally extirpated in Illinois. Although P. caprodes was col-lected at five sites including the two that housed E. triquetra, it occurred at low densities. It seems unlikely that E. triquetra can recover naturally in Illinois, and carefully planned translocation or augmentation methods might be required to restore the species.