Global Attention on Prespa: New Study Warns of Tortoise Population Collapse on Golem Grad Island

A major scientific breakthrough focusing on the tortoise population of Golem Grad in Prespa was reached in January 2026 with the publication of “Ecology Letters”. This study was authored by an international research team led by Dragan Arsovski, Xavier Bonnet, Ana Golubović and Ljiljana Tomović. Based on over a decade of research by the Macedonian Ecological Society in partnership with academic institutions from Serbia and France, and with the support of the Prespa-Ohrid Nature Trust (PONT), the study provides one of the most comprehensive insights into this unique island ecosystem.

The research analysed the life history and population dynamics of Hermann’s tortoises and revealed alarming long-term trends. Scientific models indicate that the population is heading toward collapse, with the possibility that all female tortoises on the island could disappear by 2083 if current conditions persist.

Although around 1,000 tortoises live on the island, suggesting a prosperous population, the internal structure tells a different story. The sex ratio is extremely distorted, with up to 19 males to every female, creating serious ecological and behavioural consequences. Perhaps most importantly, this study demonstrates that sheer numbers alone can be misleading, and if we have conservation in mind and as a priority detailed long-term monitoring is a must!

Mating aggression is inherent to male Hermann’s tortoises and should promote fertility in females, but the imbalance in sex ratio has led to extremely concentrated mating aggression on the island. Female tortoises face constant stress, harassment, and injury, and in some cases, they fall from the island’s steep cliffs while trying to escape, leading to death.

The initial causes of the bias in sex ratio are still not fully understood. Scientists are also investigating how the tortoises originally inhabited the island – were they always there or did they colonise it? One theory suggests that humans may have introduced the tortoises in the past, possibly with an already uneven sex ratio. Some of the oldest males have engraved markings on their shells, which may support this idea, but there is still no clear evidence.

The issue has attracted global attention, with coverage in countries such as the United States, Germany, Brazil, and South Korea, including a feature in The New York Times. Despite some public perception of the behaviour as a curiosity, experts stress that it represents a serious ecological problem.

These findings raise an important question about whether humans should intervene. To explore possible solutions, the Macedonian Ecological Society, together with Galicica National Park, are planning an international scientific meeting in Prespa, where experts will work together to define the most appropriate conservation strategy for the future of the Golem Grad tortoises.

By: “MES”

Photo caption: Hermann’s tortoises on Golem Grad Island in Prespa
(©Dragan Arsovski/Macedonian Ecological Society)