Camera-trapping for abundance estimation of otters in seasonal rivers: a field evaluation
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ORIGINAL ARTICLE
Camera-trapping for abundance estimation of otters in seasonal rivers: a field evaluation Jose María Gil-Sánchez 1 & Ezequiel Antorán-Pilar 1 Received: 7 February 2020 / Revised: 20 July 2020 / Accepted: 4 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Cryptic mammals with semi-aquatic habits, like otters, are notoriously difficult to study. Elusive behaviour, low population density, nocturnal habits and the type of continental habitat that characterize this group of species make the estimation of their population density an arduous task. Passive infrared-triggered camera devices are a non-invasive methodology that may present key advantages for the study of otter density. We have evaluated its use for the detection and estimation of the density of the Eurasian otter (Lutra lutra) in seasonal intermittent Mediterranean rivers, where the presence of dry riverbed sections between pools is usual, due to the discontinuity of flow during the summer drought. Through six camera-trapping surveys carried out in the Yeguas River (South Spain), we evaluated the efficiency of camera-trapping in different scenarios of methodological design, including a comparison with the visual census method. The results indicated that camera-trapping can be an optimal method to estimate otter abundance if some conditions are achieved, being the most important to use camera devices with fast trigger speed (0.1–0.2 s), deployed in key places over the river bed. In the case of our best-designed surveys, related to effort and efficiency of camera devices, we found that detection probability could reach asymptotic values in a relatively short time of 1 week, with negligible effects of imperfect detection. Considering the robustness of the collected data from camera-trapping (larger sample size and sampling periods), the density estimation from camera trap method (0.43 otters/km and day) was more accurate than estimation from visual census (0.12 otters/km and day). Camera traps can provide valuable information not only for population size and trends but also for other key demographic parameters, such as sex-ratio and reproduction and activity rhythms. Keywords Camera-trapping . Eurasian otter . Wildlife monitoring . Population density . Seasonal rivers
Introduction The populations of Eurasian otter (Lutra lutra, Linnaeus 1758) have undergone a slow recovery from their previous minimum levels, despite the fact that the species remains in danger in most of its European distribution (Martín et al. 2017). Currently, the Eurasian otter is catalogued as “near-threatened” by the IUCN in its global geographic range (Roos et al. 2015) and in the Mediterranean area (Jdeidi et al. 2010). This institution advises about the need for research specific aspects in this species such as population size, distribution and trends, life history and ecology, behaviour, and monitoring. However, good information on the density of this cryptic mammal has * Jose María Gil-Sánchez [email protected] 1
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