The use of Spatially Explicit Capture-Recapture models for estimating Iberian lynx abundance in a newly reintroduced population

Abstract From 2015 till 2018, 33 lynxes were released in southeast Portugal (Guadiana valley) as a result of an Iberian reintroduction project. Since then, at least 45 lynxes were born in the wild during 3 breeding seasons. In 2018, a combination of sign search and camera trapping was applied to estimate lynx abundance in the Guadiana reintroduction area, using spatially explicit capture-recapture (SECR) models with the incorporation of sex-specific parameters. A total effort of 7210 trap-days led to 218 independent lynx captures (except for yearlings), which corresponded to 22 adults or sub-adults in 50 stations (28%). The estimated population size was 22-29 individuals (adults and sub-adults) in the 723 km 2 study area, leading to a density of 3.4 lynxes (>1-year-old)/100 km 2 . Individuals were heterogeneously distributed, since most lynxes occurred in clusters with a few lynxes scattered among them. Use of space was sex-dependent and, as expected, males moved more distances than females. Apart from the estimated 22-29 over 1 year-old lynxes, the study detected the presence of 27 yearlings. The reintroduction project is still at an early stage, since the goal for a baseline population has not yet been reached (15 reproductive females) and it is therefore essential to improve organizational issues to implement a viable long-term system covering all critical areas, namely long-term replicable census for population monitoring.