Spatial Distribution and Encounter Rates of Delphinids and Deep Diving Cetaceans in the Eastern Mediterranean Sea of Turkey and the Extent of Overlap With Areas of Dense Marine Traffic

Abstract

Marine traffic has been identified as a serious threat to Mediterranean cetaceans with few mitigation strategies in place. With only limited research effort within the Eastern Basin, neither baseline species knowledge nor the magnitude of threats have been comprehensively assessed. Delineating the extent of overlap between marine traffic and cetaceans provides decision makers with important information to facilitate management. The current study employed the first seasonal boat surveys within the Eastern Mediterranean Sea of Turkey, incorporating visual and acoustic survey techniques between 2018 and 2020 to understand the spatial distribution of cetacean species. Additionally, marine traffic density data were retrieved to assess the overlap with marine traffic. Encounter rates of cetaceans and marine traffic density were recorded for each 100 km2cell within a grid. Subsequently, encounter and marine traffic density data were used to create a potential risk index to establish where the potential for marine traffic and cetacean overlap was high. Overall, eight surveys were undertaken with a survey coverage of 21,899 km2between the Rhodes and Antalya Basins. Deep diving cetaceans (sperm and beaked whales) were detected on 28 occasions, with 166 encounters of delphinids of which bottlenose, striped and common dolphins were visually confirmed. Spatially, delphinids were distributed throughout the survey area but encounter rates for both deep diving cetaceans and delphinids were highest between the Rhodes and Finike Basins. While sperm whales were generally detected around the 1000m contour, delphinids were encountered at varying depths. Overall, two years of monthly marine traffic density were retrieved with an average density of 0.37 hours of monthly vessel activity per square kilometer during the study period. The mean density of vessels was 0.32 and 1.03 hours of monthly vessel activity per square kilometer in non-coastal and coastal waters respectively. The Eastern Mediterranean Sea has several important shipping lanes within the study area. Two priority areas for deep diving cetacean and a large priority area for cetaceans were identified in the waters between Marmaris and Finike where high cetacean encounters and dense marine traffic overlapped. The current study revealed important habitats for cetaceans within the data deficient Eastern Mediterranean Sea and delineated potential risk area where marine traffic should be limited.

Cetaceans in the Mediterranean Sea: Encounter Rate, Dominant Species, and Diversity Hotspots

“…At the same time, the diversity index shows the lowest values in the domain of the continental shelf, which is dominated by the bottlenose dolphin, except for the Alboran Sea and the Aegean Sea, where the distribution of the common dolphin partially overlaps the distribution of the bottlenose dolphin, in agreement with previous studies [30,[34][35][36]. All of the other species seem to find their habitat outside the continental shelf, where the greatest bathymetric gradient allows them to find the most favourable ecological conditions, in terms of presence and abundance of prey too, again in agreement with previous findings [30,32,[37][38][39][40].…”

Genetic investigation of Cuvier's beaked whale, Ziphius cavirostris, along the coast of Türkiye and Northern Cyprus, based on mtDNA sequences

“…In the eastern Mediterranean Sea, this species is regularly seen in the southern Adriatic Sea, along the Hellenic Trench to the west of Cyprus, especially around the Finike (Anaximander) Seamount and the eastern Mediterranean Sea off Lebanon and Israel (Notarbartolo di Sciara and Tonay, 2021). The northern part of Levantine Basin, precisely the area between the Finike Seamounts, Antalya Gulf and Adana Trough, could be an important habitat for this species (Woodside et al ., 2006; Akkaya Baş et al ., 2016; Awbery et al ., 2022; Dede et al ., 2022). The Rhodes Basin and Anatolian Canyons, which comprise deep-sea upwelling zones, provide feeding grounds for cetaceans (Öztürk et al ., 2012).…”

Use of satellite imagery to estimate distribution and abundance of Cumberland Sound beluga whales reveals frequent use of a glacial river estuary

“…Panigada et al, 2017;McGuire et al, 2020). Critical habitats can also be identified as high-use areas and have been defined using satellite tag movements (Baird et al, 2012) or areas of high concentrations of the target species (Awbery et al, 2022).…”