Non-invasive UV-A photo-identification for individual recognition in olms (genus Proteus)

The cave salamander Proteus represents a flagship and keystone genus of the subterranean ecosystems of the Dinaric Karst. Currently classified as “Vulnerable” by the International Union for Conservation of Nature, its long-term monitoring is essential for understanding subterranean ecosystem dynamics and for guiding evidence-based conservation strategies. Given its protected status and the strict permitting requirements for research and monitoring, the development of non-invasive protocols is of paramount importance. The present study aims to present a non-invasive, underwater-capable photographic tracking method for this highly vulnerable subterranean species that minimizes handling-related stress and potential impacts on animal welfare. Specifically, this work explores the application of UV photography as a novel tool for the detection and characterization of individual skin patterns, enabling the recognition of over 300 individual specimens based on unique and naturally occurring morphological features. By providing a reliable means of distinguishing individuals without the need for invasive or potentially stressful traditional marking techniques, such as physical tagging, UV-based imaging may represent a valuable alternative for the long-term monitoring of olm populations. This approach contributes to the development of scientifically grounded, welfare-centered monitoring protocols that effectively balance conservation requirements with the highest standards of animal care while improving the accuracy, repeatability, and ethical sustainability of individual-based ecological studies. Importantly, although recent evidence has revealed the presence of at least two distinct Proteus species within the study area, the present imaging-based approach remains effective for the individual identification of specimens across both species. This demonstrates that the method captures sufficient inter-individual variation to reliably distinguish individuals, irrespective of their species identity, highlighting its robustness and broad applicability in sympatric Proteus spp. populations.