Islands and invasions: Eradication of nile tilapia in the Galapagos Archipelago, Ecuador

In 2006, Nile Tilapia (Oreochromis niloticus) were discovered in Laguna El Junco, a natural crater lake in the Galapagos Archipelago, Ecuador. The largest body of freshwater in the Galapagos, El Junco was naturally devoid of fishes. Galapagos National Park (GNP) technicians proposed eradicating the tilapia with rotenone. GNP and U.S. Agency for International Development/ Ecuador requested our assistance, so in 2007 we visited the Galapagos, verified the tilapia’s identity, confirmed the lake population was reproducing, and conducted surveys indicating the tilapia was likely restricted to the lake. Eradication was justified because tilapia foraging was changing the composition and abundance of the lake’s native aquatic community, negatively affecting some endemic invertebrates. Moreover, the longer the tilapia persisted, the greater the likelihood of dispersal into other inland and coastal sites. In mid-January 2008 we sampled invertebrates from the lake, reserving some in refuge tanks for later restocking. On 25 January 2008 GNP personnel applied rotenone resulting in removal of approximately 40,000 tilapia. After tilapia eradication, and once all residual rotenone in the lake had degraded, captive invertebrates were released back into El Junco to speed recovery of invertebrate communities. No live tilapia have been collected or observed since January 2008.