Translocation and re-introduction project of striped bitterling in Lake Biwa and neighboring areas, Japan

Summary

The striped bitterling (Acheilognathus cyanostigma), Critically Endangered around Lake Biwa, Japan's ancient and biodiverse lake, had gone unrecorded there for a decade before a project led by Nagoya University, the Botejyako Trust and the Lake Biwa Museum used a small surviving northern-pond population (about 57 individuals, breeding-inactive since 2005) and a captive colony descended from 63 fish rescued from a Kyoto shrine pond to rebuild founder stock for translocation. In 2007, 22 captured bitterlings along with mussel spawning hosts and host fish were released into Miyadame Pond after local residents helped drain, dry and de-alien-fish it; by 2009, 750 more captive-propagated bitterlings were released into a pond adjacent to Lake Biwa itself, alongside translocations to school and corporate biotopes across southern Shiga. Breeding was confirmed every year for four years at Miyadame Pond, though new mussel recruitment there stalled, while the Lake Biwa-adjacent pond was overrun by invasive fish, crayfish and bullfrogs, causing mass mussel die-off and reducing the bitterling population there to just five surviving individuals. In contrast, the school and company biotope populations grew steadily to roughly 2,000 individuals by 2011. Major difficulties included small founder numbers raising inbreeding concerns, illegal poaching, and unresolved questions about genetic relationships between source populations needed to plan any eventual Lake Biwa release. The project rates itself Partially Successful, noting genuine population growth in managed ponds alongside the outright failure of the flagship reintroduction site next to Lake Biwa.