Prespa bears know no boundaries: 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 how abundant they are. Tagging them with individual-specific tags is a highly demanding task and unfeasible in any real-life setting, as is the reading of any such tags. For these reasons, the abundance estimates of brown bear populations are often based on expert opinions and rarely backed by strong evidence from the field.

Previous efforts to estimate the size of the population in Prespa used questionnaire surveys to “guesstimate” the number of brown bears in the wider Prespa region. The latest survey estimated the total number to be around 60, with 35 of those in the Macedonian part of Prespa, 18 in Greek Prespa, and 7 in Albanian Prespa.

The validity of these so-called “guesstimates” is often challenged though. Fortunately, molecular genetics has recently opened up new possibilities to “tag” individual bears through genotypes obtained from genetic material that they leave behind in the environment (e.g.: faeces or hair).

This led the PrespaNet NGO network to conduct a two-year transboundary study in Prespa using novel genetic techniques to estimate the abundance of brown bears in the region. This was achieved through the project “Strengthening NGO-led Conservation in the Transboundary Prespa Basin” which was supported by PONT and the Aage V. Jensen Charity Foundation.

The overall goal 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 individual bears. In addition to estimating the brown bear abundance in the area, the study aimed to gain insight into the genetic diversity of these bears. The samples were collected from all three countries in Prespa and were processed by genetic experts from Ljubljana using next-generation sequencing methods.

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

Recaptures enable the possibility of connecting sampling locations to the same individual, giving insight into their movement and use of corridors. Notably, some of the bears cross the borders between the countries. Two male individuals have been observed to make longer excursions throughout the study area as can be seen in the figure above.

This study highlights the importance of good habitat connectivity and the use of bears as flagship species to enforce better protection of biodiversity hotspots such as Prespa. The full report can be downloaded here.

Through the study, the PrespaNet partners gained valuable know-how and hands-on field experience that can be applied to the study of brown bear population size and distribution in the area in the future and in other areas of the PONT Focus Region.