Data from a five year monitoring on Green frogs (Pelophylax esculentus complex) at the Black sea coast of north Bulgaria.

In a previous study, the authors had predicted that the local green frog population had developed adaptations to live and breed in mixoligohaline waters, however the registered in 2010 mass migration of the adults into the sea near the Shablenska Tuzla lagoon was an isolated event, conditioned by the correlated impact of defined climatic factors. To support that hypothesis, the site was an object of five-year monitoring. Additionally, other three regions with similar topographic characteristics - the Black sea shores near Durankulak lake, Ezeretz lake and the Bolata bay - were investigated. During the period of the field surveys and according to data from fishers and biologists working in the region, no further mass migration of frogs in the sea waters was detected. An isolated observation of a specimen, swimming in the sea at Bolata bay (water with conductivity of 19.55 mS/cm), leads to the conclusion that the adult green frogs from the local population are able to inhabit the sea waters, but other factors like the sea surf prevent them to colonise the sea shores. [ABSTRACT FROM AUTHOR]