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 de creased 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.
Highlights
Intense and accelerated development of the world’s coastline is increasing the interaction between coastal marine mammal species and anthropogenic-Publisher: Inter-Research · www.int-res.comEndang Species Res 34: 1–14, 2017 lined the importance of management actions to minimise potential negative effects (Richardson et al 1995a, Lemon et al 2006, Ameer 2008, Kight & Swaddle 2011)
Bottlenose dolphins were exposed to marine vessels during 51% of the time
The current study shows that marine vessels can significantly affect the behaviour of bottlenose dolphins, with dolphins being more likely to switch from their current behavioural state to diving
Summary
Intense and accelerated development of the world’s coastline is increasing the interaction between coastal marine mammal species and anthropogenic-Publisher: Inter-Research · www.int-res.comEndang Species Res 34: 1–14, 2017 lined the importance of management actions to minimise potential negative effects (Richardson et al 1995a, Lemon et al 2006, Ameer 2008, Kight & Swaddle 2011). Dusky dolphins Lagenorhynchus obscurus (Barr & Slooten 1999, Dans et al 2008), common dolphins Delphinus delphis (Stockin et al 2008, Meissner et al 2015), Indo-Pacific humpback dolphins Sousa chinensis (Van Parijs & Corkeron 2001), sperm whales Physeter macrocephalus (Gordon et al 1992), minke whales Balaenoptera acutorostrata (Christiansen et al 2013), Hector’s dolphins Cephalorhynchus hectori (Bejder et al 1999) and bottlenose dolphins (Nowacek et al 2001, Hastie et al 2003, Lusseau 2004, Lusseau et al 2006, Christiansen et al 2010, Pirotta et al 2015, Perez-Jorge et al 2017), have demonstrated both short- and longterm behavioural changes in response to marine vessels within a wide range of ecological settings. A population of killer whales Orcinus orca was able to habituate to deliberate noise pollution; they avoided harassment devices set along lines during their initial encounters, but quickly established a way in which to overcome such noise disturbance (Tixier et al 2015)
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