2018 Volume 12 Pages 27-35
The unionid mussels Cristaria plicata, Nodularia douglasiae, and Sinanodonta spp. were widely distributed in the many ponds and rivers on the floodplain of the Tone River system in the Kanto region. In recent years, however, the population of C. plicata in particular has markedly declined, and there is concern about its extirpation in many local habitats. Consequently, C. plicata is designated as an endangered species on the red list of each prefecture in the Kanto region. On 11 March 2017, we collected C. plicata in the channel of the Watarase retarding basin. The shell length of collected samples was in the range of 180–300 mm. No individuals smaller than 180 mm were found. The results indicated that recruitment in this population was not successful in recent years. As there is little information on the locations currently inhabited by C. plicata in the Kanto region, the first step in the species’ restoration process is to confirm the records of occurrence from previous reports. In addition, genetic analysis of local populations is important because other species or subspecies of freshwater mussels, possibly including C. plicata ssp. have been repeatedly introduced for fisheries in the Kanto region from Lake Biwa in the Kansai region.
