Genetic monitoring 2015
In 2015, extensive genetic monitoring of brown bears was carried out in Slovenia as part of the international LIFE DINALP BEAR project. The main purpose of the monitoring was to obtain a reliable and scientifically based estimate of the size and sex structure of the brown bear population, while also laying the foundations for long-term monitoring of the population status in Slovenia and the wider Dinaric region.
The monitoring was based on non-invasive genetic-molecular methods, which enable accurate population estimates without direct interference with the animals. The basic starting point of the method is the collection of genetic samples (mainly feces), from which the genetic “fingerprint” of each individual bear is obtained in the laboratory. In this way, it is possible to identify individual animals, estimate how many times they have been detected, and use mathematical models to calculate the number of those not included in the sampling.
Sample collection was carried out intensively from September to December 2015 and covered the entire area of permanent brown bear presence in Slovenia. An exceptionally wide network of volunteers participated in the fieldwork, mainly hunters and foresters, but also other nature experts. A total of 4,687 non-invasive genetic samples were collected in Slovenia and Croatia, which significantly exceeded initial expectations. It represents one of the most successful sampling efforts of its kind in Europe.
Laboratory analyses were performed using advanced next-generation sequencing (NGS) methods, which enabled high reliability of results and comparability of data over a longer period of time. Of all the samples processed, more than 70% were successfully genotyped, providing a high-quality database for further analysis. In addition to non-invasive samples, the analysis also included genetic data from all bears recorded as dead or captured in 2015.
Based on the capture-mark-recapture method, the lowest annual (autumn) population estimate was calculated, representing the population status after recorded mortality and before new reproduction. The results showed that at the end of 2015, there were approximately 599 brown bears in Slovenia (95% confidence interval: 545–655). This estimate already takes into account all known population losses in that year and provides a comparable basis for monitoring trends over time.
If we add reproduction, which occurs in the winter period, to this autumn estimate, we also obtain the highest annual (spring) population size. According to calculations, approximately 711 brown bears lived in Slovenia in spring 2015 (95% confidence interval: 657–767). The sex structure of the population was stable and slightly skewed towards females, which accounted for approximately 60% of the population.
A comparison of the results of genetic monitoring in 2015 with the previous census of this kind in 2007 clearly showed that the brown bear population in Slovenia had grown significantly during this period. In 2007, the autumn population was estimated at approximately 424 bears, which means that the population has increased by more than 40% in eight years. The results confirmed the long-term positive trend in the population and, at the same time, demonstrated the importance of regular, methodologically comparable monitoring.
The genetic monitoring in 2015 thus represented a key milestone in the management of the brown bear in Slovenia. In addition to providing a reliable estimate of population size, it also enabled an in-depth understanding of the sex structure, spatial distribution, and demographic processes within the population. This data still represents one of the most important reference points for assessing the status of the population and for scientifically based planning of brown bear conservation and management.