Spatio-Temporal Distribution and Stranding Records of Cetaceans Along the Romanian Black Sea

This study investigates cetacean occurrence and stranding records along the Romanian Black Sea coast between 2021 and 2025, focusing on the three resident subspecies: Tursiops truncatus ponticus, Delphinus delphis ponticus, and Phocoena phocoena relicta. A total of 1392 live individuals were documented across 188 sighting events, with T. t. ponticus and D. d. ponticus together representing 88.3% of all recorded individuals. The monthly distribution of recorded sighting events differed significantly among subspecies (p < 0.001), as did the distance of recorded sightings from the coastline (p < 0.001). Median distances were 4.40 km for T. t. ponticus, 61.78 km for D. d. ponticus, and 30.44 km for P. p. relicta. During the same period, 76 stranded cetaceans were recorded along the Romanian Black Sea coast, of which 58 were identified to subspecies level. P. p. relicta accounted for 70.7% of identified stranded individuals, compared with 11.7% of live individuals recorded during research cruises. Stranding records were most frequent in August and May, although their monthly distribution did not differ significantly among subspecies. Although both datasets covered the same geographical region and study period, differences in observation methods and sampling effort limit direct comparisons and prevent inferences about mortality rates or population trends. Nevertheless, the observed differences in the spatial and monthly distribution of live sightings, together with the high representation of P. p. relicta among stranded individuals, provide complementary information to support future cetacean monitoring, stranding investigations, and conservation efforts in the Romanian Black Sea.