Özet:

Any species in new life conditions passes through several phases or stages of naturalization. Information about time of these phases is important for analysis of changes in invader population and understanding of the role of alien species in analysed water bodies. The aim of this work is to detect the time of occurrence of naturalization phases for the kilka in the Dniprodzerzhinsk and Kremenchug reservoirs. The analysed material includes the own data, archives of the Institute of Fisheries of the NAAS, commercial fishery statistics and literature sources. A dynamic phase portrait method was applied for detailing the time of beginning of different phases. It was established that kilka had been already present in the Dniprodzerzhinsk reservoir at the phase of II (reproduction) before its construction, and after 1967 it became the predominant pelagic species. As for the Kremenchug reservoir, kilka invaded that water body 4–5 years after its construction. It quickly passed phases I and II and by 1968 became abundant commercial species. Thus, it was found that kilka’s naturalization phases occurred differently in these nearby water bodies: in the future Dniprodzerzhinsk reservoir area, this species penetrated two years before impoundment; while in the Kremenchug reservoir it penetrated four years after the construction. Four to five years were needed for passing first three phases of kilka naturalization in the studied reservoirs. Faster progression of the phases I and II of its naturalization in the Kremenchug reservoir compared to the Dniprodzerzhinsk one indicates on better life conditions in the first water body at the moment of invasion. Currently, the studied kilka populations pass the phase IV of naturalization, which is characterized by fluctuation of population abundance.

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