Line Transect Surveys of Abundance and Density of Cetaceans in the Marine Area of the Bulgarian Natura 2000 BG0001001 Ropotamo Site of Community Importance, Black Sea

The high conservation status of the Black Sea cetaceans in the IUCN Red List of Threatened Species, i.e. the Black Sea harbour porpoise Phocoena phocoena relicta and the Black Sea bottlenose dolphin Tursiops truncatus ponticus as Endangered (EN) and the Black Sea common dolphin Delphinus delphis ponticus as Vulnerable (VU) defines the importance of studies on their distribution and abundance. The paper presents results from distance sampling surveys for estimation of the density and abundance of cetaceans in the Marine Protected Area Ropotamo designated for conservation of cetaceans and marine habitats. Data were collected during five days in April and May 2016 using a motor sailing yacht. In April, all three species were observed while only harbour porpoise and bottlenose dolphin were detected in May. In all survey days, the most sighted species was the Black Sea harbour porpoise. Encounter rates varied as follows: harbour porpoise - 0.26 to 0.54; bottlenose dolphin - 0.02 to 0.07; common dolphin - 0.02 to 0.31. Density and abundance were: harbour porpoise - 1.8669 ind.km(-2) and 1468 ind. (CV = 29.46%. 95% CI: 686-3140); bottlenose dolphin - 0.13 ind.km(-2) and 103 ind. (CV = 45.98%, 95%, CI: 38-276); common dolphin - 0.516 ind.km(2) and 406 ind. (CV = 101%, 95% CI: 34-4789).

Automated summary

The study revealed that in the Marine Protected Area Ropotamo in the Black Sea, the harbour porpoise was the most commonly sighted species among cetaceans, with a relatively high abundance, highlighting the importance of the protection area for Black Sea cetaceans.