A.Population characteristics of European pond turtle on Ludaš lake in Serbia

Abstract

Ludaš lake is one of the few natural lakes in the Vojvodina province, with a water surface of 328 ha. It hosts a population of the European pond turtle (Emys orbicularis), the only autochthonous species of freshwater turtle that is inhabiting Serbia. This is an open population, connected by the canals to other adjacent (sub)populations. Such a well-established network of artificial and natural water bodies in theory might interconnect many populations of the European pond turtle in the Pannonian plain, most probably forming a metapopulation system. For the purpose of the 10 years long and still ongoing population study (Capture-Mark-Recapture), only the north portion of the lake was investigated, with an approximate surface area of 9 ha. During this study, 820 capture events occurred, amassing 397 marked individuals in the study plot. The Schnabel index for estimating population size shows that the number of individuals in the study area is 596.7. A rough estimate of population density is 66.33 individuals per hectare. The adult sex ratio is close to 1:1 (201 females vs. 188 males), which is considered very balanced. A portion of caught juveniles is only 2%, and this is most probably due to the capturing method used (baited funnel traps, which are not suitable for capturing juvenile turtles). Continuous monitoring of population parameters such as population size and sex ratio can provide useful insights into the current state of the population and can be the firm basis for future conservation actions in the areas where and when some of these parameters come out of balance.