An analysis of nighttime passive acoustic monitoring system data of bottlenose dolphins (Tursiops truncatus) in the Istanbul Strait

The Turkish Straits System (TSS) connects the Black Sea and the Aegean Sea, formed by the Çanakkale Strait (Dardanelles), the Sea of Marmara, and the Istanbul Strait (Bosphorus). This system is fundamental in terms of biodiversity, serving as a biological corridor for those migrating between the two seas. Three cetacean species are observed in the TSS, namely Phocoena phocoena (Linnaeus, 1758), Delphinus delphis Linnaeus, 1758, and Tursiops truncatus (Montagu, 1821). In the present study, acoustic data were collected with hydrophones for 21 nights in Fil Burnu Bay, which is located in the north of the Istanbul Strait and the frequency contours of the sound in the spectrogram were analyzed. A total of 7428 whistles of the bottlenose dolphins in the region were recorded and 2920 of them were examined based on the whistle contour in the audiogram. By comparing these data with the daytime data and environmental parameters previously studied in the same area, it was aimed to understand cetacean presence and activities at night. As a result of the analyzes, it can be said that there may be a local population in the region and they chose this region for activities such as feeding and socializing. Also, this area can be considered as a travel destination for mother and calf. More studies are needed in the region to get clear conclusions. Considering there are only few studies have been done on cetacean acoustics in Turkey, each new study will contribute to the determination of cetacean sound repertoires in Turkish waters.