ESR 34:1-14 (2017)  -  DOI: https://doi.org/10.3354/esr00836

Marine vessels alter the behaviour of bottlenose dolphins Tursiops truncatus in the Istanbul Strait, Turkey

Aylin Akkaya Bas1,2,3,*, Fredrik Christiansen4, Bayram Öztürk1,2, Ayaka Amaha Öztürk1,2, Mehmet Akif Erdoǧan3,5, Laura Jane Watson3

1Istanbul University, Faculty of Fisheries, 34452 Beyazit, Istanbul, Turkey
2Turkish Marine Research Foundation, PO Box 10, Beykoz, Istanbul 81650, Turkey
3Marine Mammals Research Association, Kuskavagi Mah. 543 Sok. No.6/D, 07070 Antalya, Turkey
4Cetacean Research Unit, School of Veterinary and Life Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia
5Geographical Information System Division, Department of Architecture and Urban Planning, Cukurova University, 01350 Adana, Turkey
*Corresponding author:

ABSTRACT: The non-lethal impacts of marine vessels on cetaceans are now a globally recognised threat. This study is the first to investigate the effect of marine traffic on the behaviour of bottlenose dolphins Tursiops truncatus in the Istanbul Strait, Turkey. The Istanbul Strait (also known as the Bosphorus) is one of the busiest international waterways in the world and is exposed to dense marine traffic. The effect of marine traffic, location and season on the behavioural transitions was investigated through general log-linear analysis. Further, the changes on the behavioural budget and bout duration were assessed using Markov chains. Results showed that marine vessels were the main driving force for the behavioural transitions. These changes in transitions between behaviours led to significant changes in behavioural budget and bout durations (average time in each behavioural state). Surface-feeding, resting and socialising behaviour significantly decreased in the control budget, while diving showed an increase in the presence of vessels. Moreover, dolphins spent less time surface-feeding, resting, socialising and diving once disrupted. Furthermore, the current level of vessel-dolphin interaction (51%) in the Istanbul Strait was sufficiently high to alter the dolphins’ cumulative behavioural budget significantly. Finally, speed and distance of vessels played a considerable role in the directional responses of dolphins. These results raise concerns on the potential biological consequences of the observed behavioural changes, considering that the population is already classified ‘at risk’ and is still lacking species-specific conservation plans. The results of the study must be considered immediately to create protected zones in order to mitigate the vessel-dolphin interactions.


KEY WORDS: Bottlenose dolphins · Marine traffic · Disturbance · Behavioural impacts · Behavioural budgets · Bout lengths · Cumulative behaviour · Markov chain · Conservation


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Cite this article as: Bas AA, Christiansen F, Öztürk B, Öztürk AA, Erdoǧan MA, Watson LJ (2017) Marine vessels alter the behaviour of bottlenose dolphins Tursiops truncatus in the Istanbul Strait, Turkey. Endang Species Res 34:1-14. https://doi.org/10.3354/esr00836

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