Prespa bears know no bounds: Using genetics to estimate brown bear abundance in Prespa

Estimating the abundance of brown bears in the wild is a daunting task. It’s virtually impossible to directly observe the bears and estimate their abundance. Tagging them with individual specific tags is highly demanding and unfeasible in any real-life setting, as is reading of such tags. That is why, in many cases the abundance estimates of brown bear populations are still based on expert opinions and rarely backed by any defensible data. These so-called guesstimates are in many instances followed by the often-justified skepticism in their validity. Luckily, the possibilities opened up considerably with the rise of molecular genetics, which uses state-of-the-art methods that allow individual “tagging” of bears through genotypes obtained from genetic material that they left in the environment, like feces or hair.

Following the aforementioned natural progression of research, previous efforts to estimate the size of the population in Prespa (Stojanov et al. 2012) used questionnaire surveys to guesstimate the population number of the brown bear in the wider Prespa region to be around 60, of those 35 in Macedonian Prespa, 18 in Greek Prespa and 7 in Albanian Prespa.

This led to the idea of conducting a two-year transboundary study in Prespa using novel genetic techniques to estimate the abundance of brown bears in the region, as part of the project “Strengthening NGO-led Conservation in the Transboundary Prespa Basin”, implemented by the PrespaNet NGO network.  The broader scope of the study was to estimate the dietary habits and habitat use of the brown bear through scat collection, while using the fresh samples to genotype the individuals. The sampling was conducted in all three range countries and the samples were sent to genetic experts from Ljubljana who performed the next-generation sequencing. Besides estimating the brown bear abundance in the area, the secondary goal was also to get some insight on the genetic diversity of these bears.

The genetic study revealed a minimum of 51 individuals, 19 females and 32 males in the entire study area, which is well within the expectations and in accordance with the previous guesstimates. Genetic diversity in bears in the Prespa Region seems somewhat lower than that observed in the west Balkans, but considerably higher than in the European bear populations that are known to be very small and endangered. This fits with the findings of other studies in that wider geographic region.

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Geographic distribution of collected samples with lines connecting samples of the same animal.

Recaptures enable the possibility of connecting the sampling locations of the same individual, giving insight into their movement and use of corridors (see photo). While this study did not achieve a detailed mark-recapture estimate of bear abundance in the area due to the somewhat poor quality of the samples, it did manage to produce some preliminary results of spatial patterns of bears in the region. Notably, some of the bears cross the borders between the countries, with two male individuals observed to make longer excursions throughout the study area. Results like these highlight the importance of good habitat connectivity and the use of bears as flagship species to enforce a better protection of biodiversity hotspots such as Prespa.

This study is the first of its type in the region, and the results, even though not exceptional, were perfectly acceptable for a pilot study. This allows for considerable optimism if a similar or larger study would be repeated and, considering all the field know-how and experience that was gained by the project partners, we firmly believe that a highly successful study of brown bear population size and distribution could be done in the area in the future.

You can read more about these and other interesting findings of the study in the full report on the following link.