Seasonal dynamics of occurrence and group size of three species of cetaceans (Delphinidae and Phocoenidae) on the southwestern coast of the Black Sea

Abstract

The spatial and temporal occurrence of cetaceans in the Black Sea and particularly along its southwestern coastline is poorly studied. Based on a total of 609 encounters, we present the analysis of monthly dynamics of (1) the numbers of cetacean sightings and (2) their group size for all three Black Sea cetacean species: the bottlenose dolphin (Tursiops truncatus), the short-beaked common dolphin (Delphinus delphis) and the harbour porpoise (Phocoena phocoena) over a continuous period of 29 months (January 2018 - May 2020) from two fixed coastal observation points near the city of Zonguldak, Turkey. Seasonal fluctuations were found in the occurrence of all three species, with peaks in April-May (spring). Similarly, the largest groups of P. phocoena and T. truncatus were recorded in the late spring and early summer period, while D. delphis had a peak in July (summer). In case of the harbour porpoise, we speculate that these variations can be explained by the annual migrations from the northwestern to southern waters of the Black Sea, while the seasonal dynamics of the two Delphinidae species might depend on fish prey availability. While our data were collected locally, the results provide better insight into the ecology of cetaceans within the entire Black Sea.

Seasonal abundance estimates of cetaceans in the southern Black Sea (Sinop), Türkiye

“…Seasonal variation in the oceanographic and biological conditions of the Black Sea (Demidov, 2008; Oğuz et al, 1999; Özsoy & Ünlüata, 1997) may affect the abundance and distribution of cetaceans, as observed in other regions of the world (Arcangeli et al, 2017; Becker et al, 2014; Dede, 1999; Laran et al, 2017a,b). However, there is a paucity of four‐season surveys in the entire region, except for boat‐based line‐transect surveys in Georgia (Kopaliani et al, 2015) and land‐based cetacean sightings in Zonguldak (Uludüz et al, 2020).…”