Combating adult invasive American bullfrog Lithobates catesbeianus

American bullfrog Lithobates catesbeianus is considered as one of the world’s worst alien invasive species. Currently, the species is present over almost all continents and is suspected to cause substantial ecological damage. Knowledge about its population density, as well as catchability of the species with commonly used sampling gear, is very useful when considering the development of sound population control programs. Using the multiple mark-recapture method, we investigated the density, sex ratio, and mobility of an adult bullfrog population inhabiting several neighbouring small shallow ponds at the peak of reproduction (mid June–mid July). We estimated the density at 4.3 adults/100 m shore length and the sex ratio (males/females) to 1.64. On average, males and females moved 25 and 83 m, respectively. Catchability of adults, using one double fyke net for 24 h, was rather constant and equalled 0.7 % of the population size. At first sight, this capture technique seems not to generate large-scale adult removal. However, as a companion study revealed that double fyke nets are highly effective for capturing tadpoles, control or even eradication of isolated populations may be enhanced when this proportion of the adult segment is equally removed.