The presence of piscivorous vertebrates at fish farms often ignites conflicts over fish resources managed by humans. This study investigates the factors affecting the presence of conflict vertebrates at fish ponds. A telephone survey in western Poland in 2012-2013 examined 104 fish ponds. Six species were most often observed at fish farms: European otter Lutra lutra (87 % at farms), grey heron Ardea cinerea (83 %), great cormorant Phalacrocorax carbo (67 %), great egret Ardea alba (42 %), Eurasian beaver Castor fiber (37 %) and American mink Neovison vison (31 %). American mink, Eurasian beaver, great egret and grey heron were more often present at carp ponds. Eurasian beaver, European otter and great cormorant were present more often at larger ponds. Latitude significantly affected the occurrence of great egrets (more frequent in the south). European otter and American mink were present more often at ponds supplied by river water. Ponds supplied by river water may provide both species opportunity to enter imperceptibly to farms, with no need to exit water. Methods of pond protection and proximity of buildings to farms did not significantly affect the presence of conflict species. The data from this study concerning the presence of piscivores at ponds may serve as base for more comprehensive studies investigating the impact of these species on fish farming practices as well as for comparative and experimental studies on the effectiveness of various mitigation measures. Regular surveys of species occurring at ponds may be a tool of monitoring invasive species as well as species increasing its range.

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We analysed hydrographic and habitat factors influencing the location of 207 colonies of the grey heron Ardea cinerea in Poland. We compared areas of particular habitats in three buffers around colonies (0-1, 0-10, 0-20km) among eight regions differing in their proportions of studied habitats. We found the highest inter-region dissimilarities in areas covered by water bodies (all scales) and pastures (0-1km). We recognized some indicator habitats characteristic of the majority (water bodies, pastures) or of some (seacoast, inland marshes, urbanized zone) regions. The habitat selectivity index showed that grey herons in buffer 0-1km preferred pastures and water bodies in seven regions and rivers in one subprovince. In buffer 0-10km, forests and urban zones were preferred in seven and five subprovinces, respectively. Our study revealed that both aquatic and non-aquatic habitats are important for the distribution of the grey heron colonies in Poland.

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