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. 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 1 day each were enforced by bad weather but that didn’t alter the plan significantly.
The survey team successfully covered 424 km on effort from the planned transects during favourable weather conditions within 5 days. During the survey, the observers recorded 242 sightings in total with 350 individuals. Most numerous were encounters of Black sea harbor porpoises (Phocoena phocoena relicta) – 169, followed by Black sea common dolphins (Delphinus delphis ponticus) – 42 and rarest were those of Black sea bottlenose dolphins (Tursiops truncatus ponticus) – only 27. In 4 of the sightings species wasn’t identified.
The current survey is the second one organized by Green Balkans NGO in past 2 years. This year the coverage was bigger – 424 km of line transects compared to 330 km last year. Though number of sightings this year was significantly higher (8 times) – 242 compared to 30 during last year survey held in end of May. Though similar trend in distribution was detected in both years for higher number of sightings and density in the northern and southern sectors compared to central one. Most of the sightings were of solitary individuals and largest observed group this year was 8 bottlenose dolphins compared to 11 last year. During the survey, non-typical surface behavior of common dolphins was observed – short showing, no jumping, elusive – more like that of harbor porpoises. The low number of encounters with bottlenose dolphins (largest Black sea cetaceans) was other surprise – species that was more frequently encountered compared to common dolphins 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 Polina Hristova, Teodora Ilieva, Nikolay Davidkov and Antonia Miteva who has proven that trainings within “Citizens’ support for study of Black Sea cetaceans along Bulgarian coast” project have been successful. 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).
