The re-introduction of the Ushimotsugo minnow in Gifu Prefecture, Japan

Summary

The Ushimotsugo minnow, a Critically Endangered cyprinid endemic to central Japan's Tokai region, had been reduced to about ten irrigation ponds by habitat destruction and invasive predatory bass and bluegill before a coalition including Gifu Prefectural Research Institute, Gifu World Fresh Water Aquarium, local city offices and the volunteer Gifu Mino Ecological Research Group formed a conservation group in 2005 to breed and reintroduce the species. The group bred minnow stock from one surviving Seki-area population, dividing it into rotating sub-stocks to limit inbreeding, then in autumn 2005 fully drained an irrigation pond that held invasive black bass, bluegill and non-native carp but no native fish, posted legal-protection signage, and released the captive-bred stock under community monitoring that successfully deterred poaching and illegal bass releases; a second pond inaccessible to the public was also stocked that year, and two further ponds were drained and restocked in 2006. Post-release monitoring found the two 2005 ponds developed satisfactory, growing minnow populations, with the closed pond in particularly good condition and gaining native aquatic insects, though the public pond suffered an explosive 2007 invasion of non-native crawfish once bass removal lifted predation pressure, requiring ongoing manual crawfish control. The two 2006 reintroductions failed outright, with no minnows found by 2011 amid competition from other native cyprinids that had moved in. Major difficulties included a scarcity of predator-free potential release sites and balancing minnow reintroduction against habitat needs of other endangered insects and plants. The project rates itself Partially Successful, citing successful captive breeding and two established populations against two failed attempts.