First documentation of rough-toothed dolphins (Steno bredanensis) in the Eastern Mediterranean Sea of Türkiye

04/29/2025 Arda Tonay

First documentation of rough-toothed dolphins (Steno bredanensis) in the Eastern Mediterranean Sea of Türkiye

Aylin Akkaya, Atakan Dalkılıç, Tim Awbery, Ceyda Ozdemir, Patrick Lyne

ORCID IDs: A.A. 0000-0002-0414-770X; A.D. 0000-0001-7612-6740; T.A. 0000-0003-4338-8351; C.O. 0009-0005-1445-928X; P.L. 0000-0002-8326-5180

DMAD-Marine Mammals Research Association, 19 Mayıs Mah İnönü Cad Esin Sok 11/7, Kadıköy, Istanbul, TÜRKİYE

Abstract

Despite the global distribution of rough-toothed dolphins (Steno bredanensis), they remain an understudied species within the Mediterranean Sea, with only a handful of sighting and stranding reports within the entire basin. In the current study, an area of 3,922 km² between Fethiye Bay and the Finike Trough in the Eastern Mediterranean Sea of Türkiye was surveyed using a standard line-transect distance sampling approach. The survey was conducted over 10 days, from 12 to 21 July 2024. The survey methodology incorporated visual observations, acoustic data collection, and drone-based surveys. On 18 July 2024, an unidentified delphinid species was first acoustically detected at 04:06 in waters with a depth of 1,000 m. Later that same day, a visual detection of rough-toothed dolphins occurred at 14:40 in waters with a depth of 2,000 m. Both detections were located within the Finike Trough, off the coastal town of Kas. Post-acoustic analysis confirmed that the initial acoustic detection was also of rough-toothed dolphins. These detections are likely to represent the same encounter, given that it is likely that the short distance of 10 km can be travelled by the group within a 10-hour period. The focal group of the visual encounter consisted of 11 individuals, including two sub-adults, with multiple subgroups observed in tight formations, moving fluidly. During the encounter, the species showed no visible avoidance behaviour towards the research boat. Both non-harmonic and harmonic whistles were predominantly associated with diving and interactions with the research boat, while burst pulses were more frequent during diving activity. Upsweep whistle contours, with most energy below 10 kHz, were the most dominant whistle type, with segmented upsweep and wave shape harmonics notably prevalent in their tonal sound patterns. This study documents the first confirmed encounter with rough-toothed dolphins in Turkish waters and contributes to our understanding of the visual and acoustic behaviour of this species in the Eastern Mediterranean Sea.

Keywords: Steno bredanensis, Levantine Basin, distribution, vocalisation, behaviour

Pages: 1-24

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