Large numbers of small cetaceans (common dolphin, harbor porpoises and bottlenose dolphins) were hunted in the Black Sea until the hunting of cetaceans was banned in Turkey in 1983. Even though the practice of hunting cetaceans has ceased by Turkish fleets, ongoing threats such as viral infections, overfishing, by-catch, habitat loss, seismic surveys and the pressure of fishermen continue to persist. One of the most overwhelming reasons as to why overcoming these threats proves so difficult, is the insufficient data available for these populations.
This thesis study aims to evaluate the distribution and abundance of the Black Sea cetaceans for the future conservation of these species. To fulfill this role, i) hydroacoustics, ii) passive acoustics and iii) visual observation methods were performed over transects during two one month cruises held in July and October 2014, covering up to 120 miles off the Black Sea coast of Turkey (approximately 150 000 km2). For the fisheries hydro- acoustics, three scientific echo sounders (38 kHz, 120 kHz and 200 kHz, SIMRAD EK60) were operated continuously over the cruise transects. For the passive acoustics, C-POD (Chelonia Ltd., Cetacean Monitoring Systems) was deployed at up to the 93 stations. In addition, a new methodology for cetacean detection was developed. During the development of the new methodology, dolphin presence in fisheries hydro-acoustic data, i.e. the “noise”, was processed into the “data” by validation with cetacean observation data. C-POD data was used both for confirmation of cetacean species and characterization of cetacean vocalizations. Finally, the abundance of cetacean species in the Exclusive Economic Zone of Turkey were examined using the data generated by the three respective methodologies.
With the combination of these methods, the distribution of especially one vulnerable (IUCN) Black Sea cetacean, the short-beaked common dolphin (Delphinus delphis ssp. ponticus, Barabash-Nikiforov, 1935) was assessed. Results suggest that cetaceans, especially common dolphins, are concentrated mainly in the Eastern region of the Black Sea and harbor porpoises are distributed coastally in lesser numbers. Furthermore, bottlenose dolphins were scarcely observed in the study area. As a result of abundance estimations it was found that, common dolphins display the largest population size, followed by harbor porpoises and bottlenose dolphins, respectively. Additionally, comparisons with 11 years of past visual observation data demonstrated an overall decrease in Black Sea cetacean populations. Lastly, the methodology developed proved that the hydro-acoustical data collected for fisheries purposes can also be used in cetacean research.