Initial study on the presence of the smooth newt (Lissotriton vulgaris) in ponds on the island of Krk, Croatia

The karst ponds on the island of Krk (situated in the Kvarner Bay of the North Adriatic Sea, Croatia) are important freshwater and brackish habitats at a local and regional level. The origin of the ponds is mostly anthropogenic, used for livestock and agriculture throughout history. In the environment of the island where water bodies are scarce, karst ponds are important habitats for survival of amphibians. The smooth newt (Lissotriton vulgaris) is the only newt species that inhabits the island of Krk. Although listed as of Least Concern at the global and European scale, the Krk population of smooth newts faces severe threats, dry up of ponds and introduction of invasive fish species. The biggest threat is the mosquitofish (Gambusia holbrooki) which predates on smooth newt eggs and larvae. The objective of the present study was to emphasise the importance of these unique water bodies as breeding habitats for the survival of the smooth newt population. In the period between May and June 2017, 5 ponds were surveyed in order to determine habitat features important for amphibians and to confirm the occurence of the smooth newt. Geographic positions of the investigated ponds in the surveyed area are: Skala – N45° 01.012' E14° 40.436', Kaljužina – N45° 00.722' E14° 40.521', Nova lokva – N45° 00.457' E14° 40.990', Kimpi – N45° 02.107' E14° 33.513' and Misucajnica – N45° 03.288' E14° 39.017'. Data collected during the fieldwork that will be used for successive analysis were: pond area, depth, vegetation, presence of fish and other pond fauna. Ponds were also characterized in terms of physico-chemical characteristics. The presence and abundance of the smooth newt were established by sampling according to standard methods for amphibians. We used water net as sampling technique. During the study period 15 newts were recorded in the Skala pond, 8 in Kaljužina pond and 10 in Nova lokva pond. During the inventory it was observed that smooth newt only inhabit ponds in which there are no mosquitofish. In 2 ponds, Kimpi and Misucajnica, the mosquitofish were abundant and the presence of newts was not recorded. Further going on is monitoring of additional demographic parameters and monitoring of the occurence and effect of alien species. The study contributes to defining the threats and conservation status of the Krk population of smooth newts.