Abstract
Before being found in Kasama Pond in November 2014, Limnoperna fortunei, the golden mussel, had not been observed anywhere in the Naka River system. Kasama Pond is fed from Lake Kasumigaura, where the species has been reported since 2005. To evaluate the introduction and distribution of L. fortunei in the Naka River system, we investigated the population in Kasama Pond from December 2014 to May 2015. We also surveyed a canal, a pond, and two rivers connected to Kasama Pond. In Kasama Pond, we found L. fortunei along half of the shoreline, and collected most individuals near the inflow from Lake Kasumigaura. Based on size-frequency data and previous reports, the first infestation in Kasama Pond must have occurred no later than 2013. Although we also found L. fortunei in a canal that flows from Kasama Pond, we did not detect it in rivers or another pond (Fudo-yatsu Pond) connected to Kasama Pond. To reduce damage from L. fortunei and slow its spread in the Naka River system, it will be necessary to eradicate the species from waterbodies fed from Lake Kasumigaura.
