İNŞaat mühendiSLİĞİ anabiLİm dali

Investigation on the Interactions Between Cetaceans and Marine Traffic ın the İstanbul Strait
The Istanbul Strait lies between the Black Sea and Marmara Sea and has been known as one of the narrowest and busiest straits in the world with the minimum distance of 698 m between the European and Asian coast. Concomitant with its economic value for shipping, fishing, and recreation, the Istanbul Strait also plays a vital role for marine life. Three species of Cetaceans, bottlenose dolphin (Tursiops truncatus), short-beaked common dolphin (Delphinus delphis) and harbor porpoise (Phocoena phocoena) are frequently observed in the area. Cetaceans react to marine traffic either with short or long-term behavioural changes. However behaviour budgets are directly related to an animal’s energy budget, thus, changes in their behaviour pattern, even a short-term reaction, result in energy depletion for that individual. These individual effects can eventually contribute to long-term concerns for the population. Through this study we intend to differentiate the effect of marine vessel presence on the behaviour of Cetaceans in the Istanbul Strait. However the information on the marine vessel presence alone, by no means, can explain the dimension of its effect. Therefore the effect of different type of vessels, their densities, speed and routes on the dolphin reaction were analysed under seasons and sections. We were also interested in determining if the marine vessel pressure could have detrimental long-term effects such as increased energy expenditures. As such, not only the reactions of dolphins towards different vessels, their distance and densities were analysed but also behavioural transitions were investigated through the development of Markov chains. Moreover, residency patterns of photographed bottlenose dolphins were also analysed to deepen the understanding on the socio-dynamic structure of the population.
This study aims to provide insights into the importance of delineating MPAs according to their critical habitat features by combining behavioural data with locations of high dolphin concentration and dense marine traffic. Moreover, identifying the residency patterns and social structure of these dolphins serves as a tool on the delimitation of critical habitats. Therefore a photo-identification study of bottlenose dolphins was also conducted throughout the study.
A total of 439 sampling period were carried out. The Istanbul Strait as a whole serves as a critical habitat for all three species of Cetaceans throughout the year. When we specify the critical habitats under seasons, south section serves as a critical habitat for bottlenose dolphins for whole year however particular attention should be given during summer, autumn and winter. While, harbour porpoise possesses a small size of critical habitat in the south section for summer, there was no critical habitat documented for common dolphins in the south section. Middle and middle-north section serves as a critical habitat for all three species. While it is important during spring and summer for bottlenose and common dolphins, it carries an all year importance, particularly during spring and winter, for harbour porpoise. North section serves a critical habitat for all three species as well. While bottlenose dolphins and harbour porpoise possess critical habitats in the area during spring, summer and winter, it is important for common dolphins only for spring and summer. Cetacean sightings were high, with more than 60% chance of spotting dolphins, for all seasons except autumn. It drops to around 30% in autumn for all sections but south. In autumn, high density of fishing vessels was observed throughout the strait. In addition, middle and middle-north section which has the highest marine vessel concentration had the least Cetacean sightings. The reason for these drops can be the long term avoidance strategy to avoid the high density of fishing vessels and marine vessels in the area. Therefore the decline on Cetacean sighting might already be a long term reaction of dolphins towards marine vessel presence through area avoidance.
Moreover, even though diving was significantly increased on the impact chain for bottlenose dolphins and common dolphin, the control and impact budget of Cetaceans in the Istanbul Strait was not different from each other. Therefore dolphins in the strait compensate the effect of marine vessels by avoiding surface active behaviour and increasing their diving intervals whereas harbour porpoise were actively avoiding the vessel present area.
Highest negative reactions were recorded for high speed ferries, high speed boats and ferries while the magnitude of negative reaction was highest if the distance between vessels and group was less than 100 m. Also increasing density of vessels was resulted in less surface-active behaviour.
Resting and socialising behaviour of Cetaceans in the strait was rare throughout the year. As there is no previous data, the comparison of current situation is impossible. However as it was pointed out in the previous studies, socialising and resting behaviour were the first behaviours, that would be affected from the marine vessel presence. Therefore the reason behind the few sightings of resting and socialising can be the long term effect of marine vessels and Cetaceans in the area is either reacted by displacing those behaviours somewhere else in Marmara and/or Black sea or engaging with those behaviours at night when the traffic density was comparably low.
Lastly, it was found that the bottlenose dolphins in the Istanbul Strait have a heterogeneous community and the network was highly connected and has many direct and indirect connections between individuals. Even within the small sample analysed, certain individuals serve key positions and their presence may be vital to maintain the cohesion of the community. Continuous presence of the same dolphins throughout the research period shows the existence of a stable but yet mostly unknown and complex population of bottlenose dolphins.
In conclusion, this study delineate the critical habitats in the Istanbul Strait for all three species in details and provides the base on the understanding of residency patterns and social structure of and is meant to serve as a tool for the development of conservation strategies and establishment of protected areas.