Date

2019-10-04

Author

Başkır, Saba

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Cetacean hunting was banned in Turkey in 1983. In the following decades, as the ecological shifts in the Black Sea occur, over-increase in the cetacean populations were hypothesized as the cause of the decline in economically valuable pelagic fish species like Anchovy (Engraulis encrasicolus) and Sprat (Sprattus sprattus). These arguments create the pressure of re-legalization of direct killing of cetaceans, whom are assumed to be foraging mainly on Anchovy. These arguments, although raise concerns from the fishery economy aspect, lacked scientific foundation due to absence of cetacean foraging studies in the Black Sea. Therefore, this thesis study aimed its efforts at determining cetacean distributions and their foraging habitats in the Turkish waters of the Southern Black Sea, to explore whether the assumptions of highly overlapping prey preference and competition of resources did actually hold. For this purpose, active acoustics data that was collected for Anchovy Stock Assessment research was utilized, with the implementation of recently developed algorithms that enable extraction of cetacean distributions, from the vocalization marks from the echograms. The extracted vocalization marks from the clicks that are assumed to be in higher occurrences during foraging, are quantified within 1nmi running radius. These foraging activities were then compared with the pelagic fish abundances that were analyzed via echointegration techniques from the data active acoustic data set of November 2016. Both pelagic species, showed high abundances in the western coast of the Southern Black Sea, whereas cetacean distribution and foraging areas were observed dominantly in the eastern coast of the Southern Black Sea. When the cetacean and pelagic distributions were analyzed for spatial and temporal overlap both within layers in the water column and at different times of the day, results showed no significant positive linear correlation between the mentioned top predators and Anchovy. These results are indicative of the inoperative assumption of cetacean foraging pressure playing a significant role in the declining of the Anchovy stocks. Cetacean encounters were shown to be correlated with Sprat distributions, during Night time form the presented GAM results. Therefore, outcome of this study is aimed to be of consideration in management and conservation strategies in the Black Sea. The methodology used in this study is an innovative approach to cetacean ecology studies, which is opportunistic in nature, is holding great potential for the research of cetacean foraging with the enabling the use of existing concurrent data sets of predator and prey, and further potential of development.

Subject Keywords

Acoustics, Cetacean, Foraging Areas, Black Sea, Pelagic Distribution

URI

https://hdl.handle.net/11511/95081

Collections

Graduate School of Marine Sciences, Thesis