Abstract

Invasive African clawed frog Xenopus laevis (Daudin, 1802) are considered a major threat to aquatic environments. Beginning in the early 1970s, invasive populations have now been established throughout much of central Chile. Between September and December 2015, we studied a population of X. laevis from a small pond in Vifia del Mar, where we estimated the population size and evaluated the use of hand nets as a method of control. First, by means of a non-linear extrapolation model using the data from a single capture session of 200 min, a population size of 1,182 post-metamorphic frogs (range: 1,168-1,195 [quadratic error]) and a density of 13.7 frogs/m(2) (range: 13.6-13.9) of surface water were estimated. Second, based on 10 capture-and-removal sessions of 60-min and separated by approximately 2 weeks each, a total of 2,184 post-metamorphic frogs were removed, but the number of captured individuals did not significantly decrease over time. Additionally, using novel records of its occurrence, we updated the distribution range of X. laevis in Chile, estimated at 36,055 km(2) , which is 1.7 to 3.5 times higher than previously assessed. Our results indicate that invasive X. laevis can reach extremely high densities, and removal of individuals in large numbers was not useful in reducing its abundance. This study shows that control and eradication of X. laevis from invaded areas proves extremely difficult, particularly when populations are wellestablished and/or expanding, as occurs in Chile. Our study reports the first record of X. laevis invading rivers of north Chile, 380 km north of previously reported. A management plan is urgently needed to prevent its further spread, and subsequent impacts on biodiversity. We propose our model and methodology as a tool to estimate and compare X. laevis densities. while suggesting the need to explore other control techniques in order to identify cost-effective strategies to contain the spread of X. laevis into new areas.