Estimation of Cetacean abundance and distribution in Sinop coasts of Black Sea

In this study, the seasonal abundance and distribution of cetaceans (whales, dolphins and porpoises) in Sinop region, one of the essential fishing areas of the Black Sea, were estimated with line-transect method widely used in the marine mammal population size studies. Ship based visual observations were conducted seasonally between May 2019 – March 2020. It was determined that three Cetacea species living in the Black Sea were also present in the Sinop region and their estimated population sizes were 1058 individuals for harbour porpoise (Phocoena phocoena relicta) (CV = 19.25%, 95% CI = 725-1542), 188 individuals for bottlenose dolphin (Tursiops truncatus ponticus) (CV = 21.67%, 95% CI = 123-289) and 311 individuals for common dolphin (Delphinus delphis ponticus) (CV = 16.77%, 95% CI = 123-427). The variation of the estimated abundances between seasons was significantly important and the population size of all three species increased in spring season. It has been also determined that harbour porpoises and bottlenose dolphins were present in the study area throuhout the year, while common dolphins absolutely leaved this region in winter. The findings of this study suggest that Sinop is one of the wintering grounds for harbour porpoises; further, it is thought to represent a critical area in terms of feeding, mating and offspring activities for all three species in the spring season. This study is the first seasonal line-transect study conducted on cetaceans living in Turkish waters of the Black Sea.