Ecological notes on the Cát Bà gecko Goniurosaurus catbaensis, a species endemic to the limestone karst islands of northern Vietnam

The Cát Bà gecko Goniurosaurus catbaensis is endemic to Cát Bà and Ha Long islands of Vietnam. The ecology of this species is still scarcely studied but previous reports have suggested that the species is Endangered due to small population size and low ecological plasticity. We studied aspects of the ecology of this species between May 2019 and June 2020, along seven transects on Cát Bà island. At least 173 different individuals (possibly as many as 189) were recorded, with an equal sexratio and apparently no intersexual differences in adult body size. The species was clearly more widely distributed than previously supposed. We were able to confirm that G. catbaensis is a limestone karst microhabitat specialist, as the farthest sighting from a karst area was only 10 m. Geckos were observed at a mean height of 45 cm but up to 500 cm above ground, with males perching significantly higher than females. We observed these geckos at altitudes ranging from 11 to 228 m a.s.l.; much higher than previously recorded. Overall, our study revealed that this endemic gecko is certainly less threatened than previously feared.