News

Cetacean survey in Bulgarian territorial waters of the Black Sea

Cetacean survey in Bulgarian territorial waters of the Black Sea

28.06.2018
In the period 03-08 June, a team of Green Balkans’ experts and volunteers executed a vessel survey on abundance, distribution and density of cetaceans’ population in Bulgarian territorial waters of the Black Sea. Territorial sea of Bulgaria includes strip with a width of 12 nautical miles adjacent to the coast and the internal waters measured from the baselines with total area of 6 358 sq. km.
 
The internationally proven and used technique of distance sampling along line transects was used. The survey plan was developed using the standard software for distance sampling – Distance 7.0 – and included 13 transects with total length of 458 km on effort ensuring coverage of 7% on study area. Main limiting factor for the successful execution of the survey was the meteorological conditions at sea as for the visual observations were needed good conditions – low wind and waves. During the week when the survey was made only two interruptions of half day each were enforced by bad weather but that didn’t alter the plan significantly. Though compared with last year survey in June weather conditions were slightly worse but still within the allowed conditions for executing visual surveys.
 
The survey team successfully covered 441 km on effort from the planned transects during favourable weather conditions within 5 days. During the survey, the observers recorded 55 sightings in total with 92 individuals. Most numerous were encounters of Black sea harbor porpoises (Phocoena phocoena relicta) – 39, while for Black sea common dolphins (Delphinus delphis ponticus) and Black sea bottlenose dolphins (Tursiops truncatus ponticus) were recorded 7 sightings each. In 2 of the sightings species wasn’t identified.
 
The current survey is the second one organized by Green Balkans NGO deploying the same design in order to monitor trend in distribution, density and abundance of cetaceans in Bulgarian territorial waters. This year the coverage was bigger – 441 km of line transects compared to 424 km last year. Though number of sightings this year was significantly lower (almost 5 times) – 55 compared to 242 during last year survey held in mid-June. Distribution was slightly different compared to previous year. Most of the sightings were of solitary individuals and largest observed group this year was 8 bottlenose dolphins just like last year.  
 
Collection of information on distribution and abundance of cetaceans is important for conservation of these enigmatic species. Data from the survey will be analyzed so to get an estimation of abundance for different species in the relevant period.
 
We would like to thank volunteers Galina Meshkova, Polina Hristova, Teodora Ilieva and Antonia Miteva who have proven as experience observers once again and allowed continuity of the study. Special thanks to captain Georgiev with “Kaliakria” yacht for the professional logistic support. 
 
The survey was made possible thanks to the generous funding provided by OceanCare (www.oceancare.org).