Date

2019-10-04

Author

Bilir, Batıkan

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It is known that the temperature change in water resulted by the strength and direction of cold winds varying from year to year has an effect on the distribution of small pelagics which have yearly migration cycles in semi-closed systems such as Black Sea. However, how small pelagic species wintering in the southern Black Sea have adopted to this situation has not yet been elucidated. The aim of this study is to determine how the wintering distributions of three small pelagic fishes, Black Sea Anchovy (Engraulis encrasicolus ponticus), Mediterranean Horse Mackerel (Trachurus mediterraneus) and Sprat (Sprattus sprattus), dominant in the southern Black Sea region change in two different years with different cooling rate and direction from a rational point of view. To this end, the region between 28°E and 42°E longitudes of the southern Black Sea was examined to the limit of the exclusive economic zone. The surveys carried out in 2011 and 2016 was funded by TUBITAK (The Scientific and Technological Research Council of Turkey) for the project titled “Determination of Anchovy Stocks in the Black Sea by Acoustic Method and Setting of Continuous Monitoring Model” within the scope of 1007 projects. Within the scope of these expeditions; CTD, trawl and acoustic data were collected simultaneously. Then, CTD data were analyzed for two separate years to determine the thermocline line and implied to the acoustic data. As a result of this process, the shapes of horse mackerel schools were determined and the structure (height, weight, energy distribution etc.) of these schools were quantified before separating the cold water species, sprat and warm water species, anchovy. For this procedure, schools verified as horse mackerel were used. The schools in the rest of data set were determined according to ranges of these parameters. Afterwards, horse mackerel schools were removed from the data set and the acoustic data which were divided into two separate layers were analyzed for anchovy and sprat. According to the results, all three small pelagic species settled in the wintering area due to cooling resulted from northern winds. In detail, while the adults of anchovy and horse mackerel, which are hot lovers, are mostly observed on the shore, juvenile individuals which have tolerance colder waters, of the same species and sprat were more intense in the open sea. Regarding the coastal zone, anchovy was observed in the eastern, and horse mackerel spread in the western part of the central and eastern parts of the southern Black Sea in 2011. This shows that cold water tolerance of the horse mackerel were more than anchovy in the year 2011. As a result of north-south cooling in 2016, anchovy was distributed in the west and about 10-fold less than that in the east which are probably came from north. Similar to the state of anchovy, horse mackerel was concentrated in the west in 2016. It was finally observed that sprat prefers open waters in winter and the density which is less on the coasts increases in colder regions.

Subject Keywords

Small pelagic fishes, wintering distribution, cooling pattern, hydroacoustic survey, thermocline, Southern Black Sea.

URI

https://hdl.handle.net/11511/95080

Collections

Graduate School of Marine Sciences, Thesis