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

Nastassia Uluduz,Alexey Yanchukov,Mustafa Sözen

doi:10.3989/scimar.05086.21a

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.

Highlights

The Black Sea is home to three cetacean species with global distribution: the bottlenose dolphin (Tur siops truncatus), the short-beaked common dolphin (Delphinus delphis) and the harbour porpoise (Phoco ena phocoena)
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
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

Summary

Introduction

The Black Sea is home to three cetacean species with global distribution: the bottlenose dolphin (Tur siops truncatus), the short-beaked common dolphin (Delphinus delphis) and the harbour porpoise (Phoco ena phocoena). They are found in the entire Black Sea and the neighbouring Sea of Azov, the Kerch Strait and the Turkish Strait System (BSC 2008) and are thought to have colonized the region in the Late Pleistocene (Viaud-Martinez et al 2007, 2008, Tonay et al 2020). The simultaneous use of the waters by cetaceans and humans leads to disruption of dolphin habitats and their behaviour due to the effect of such factors as oil pollution, loss of habitats and food resources (BSC 2008). In order to assess the impact of anthropogenic disturbance, it is important to know the occurrence and seasonal changes in habitat use by cetaceans

Methods

Results

Discussion

Conclusion