A new underwater camera trap for freshwater wildlife monitoring

Abstract Amphibians are among the most threatened groups of vertebrates worldwide and spend a significant part of their lifecycle in freshwater ecosystems. As for many freshwater organisms, monitoring their populations is limited by the lack of robust and standard methods applicable across large spatial scales. Here, we propose a new underwater camera trap (UCT) offering the potential to improve the monitoring of freshwater organisms that are difficult to survey, with a focus on amphibians, more specifically newts. This UCT is immersed in water and is designed to channel animals in front of a camera coupled with a motion detection system. Animals enter freely in the UCT through funnels, their underside is shot, and they can exit at any time. The ventral part of the body displays the most interesting features for species, stage or sex recognition and even for individualisation in some species. The UCT produces standardised images where the background is uniform, the animals are evenly illuminated, their distance to the camera is fixed and the shooting angle is controlled, thereby facilitating the automation of image processing and analysis. With images on a wide range of freshwater organisms collected during its field deployment on an experimental site, we show the potential of this UCT for generating new information with an unprecedented temporal granularity and for addressing novel scientific questions related to the composition of freshwater communities. Focusing on the Great crested newt ( Triturus cristatus ), a species of conservation concern in Europe, we illustrate the usefulness of this new device to estimate population dynamics or to understand behavioural responses to environmental pressures such as climate change. The UCT produces high‐resolution time series of automatically recorded and standardised images of freshwater animals at various development stages without any handling of the organisms. Beyond newts, it can contribute to improving the study of a much wider range of species in freshwater ecosystems. Technical improvements and adjustments are being explored to broaden its scope of application and make it available to a large community of users.