During the process of public discussion regarding the Appropriate Assessment Study (AAS) for the construction of the Hydro Power Plant Ombla impacts on the NATURA 2000 Paleoombla - Ombla, CBSS has submitted its comments to the Administrative Department for Protection of Nature and Environment of Dubrovnik-Neretva County. In the comments it is stated that adverse impacts to both protected species and to cave habitat 8310 within Paleoombla - Ombla Site can not be excluded and therefore we consider this project unacceptable. The comments to the AAS have also been referred to the relevant Ministries, Croatian Government, Croatian representatives in European Parliament, SIBIOS (International Society for Subterranean Biology), IUCN, (International Union for Conservation of Nature) and many others NGOs, scientists and experts. The international scientific community has supported the CBSS by sending open letters to the Croatian Government to protect and conserve Paleombla - Ombla Site, one of the world's most prominent underground habitats.
The main conclusions and comments on the Appropriate Assessment Study (AAS) are as follows:
1. Vilina špilja - izvor Omble Cave System is a rare and unique karstic phenomenon. It harbours extremely rich cave fauna, with 67 troglobionts and stygobionts (species living exclusively in caves), and one of only 7 caves in the world with more than 40 true cave dwelling species. It is a habitat for the 6 Natura 2000 conservation target species of the Paleoombla-Ombla Site, 5 bat species (Rhinolophus ferrumequinum, Rhinolophus. euryale, Myotis blythii, Myotis emarginatus and Miniopterus schreibersii) and a fish species Delminichthys ghetaldii, which was added to the Site in September 2014 after the official review of Natura 2000 ecological network proposal for Croatia by European Topic Center for Biodiversity and EU Commission.
2. The statistical analyses used in the AAS were inadequate, leading to wrong conclusions. There are two main issues. First, in the "Preliminary biodiversity estimation of cave habitats of Dubrovnik region" the correlation of the species richness and cave volume is misinterpreted. The given statistical analyses clearly show that more data should be taken into consideration to adequately interpret the species richness of analyzed caves. Second issue is misinterpretation of collection efforts which was based solely on the correlation of numbers of collector/collection days per each cave, and none of scientifically recognized methods were used (e.g. species accumulation curve, ICE, ACE, Chao, Jackknife, Bootstrap).
3. The habitat 8310 Caves not open to public is misinterpreted and expanded to all subterranean habitats (interstitial habitats, superficial subterranean habitats), leading to inaccurate assessment of the impact of planned activity to the habitat.
4. The assumption of spatial redistribution of species has no scientific ground or data to support it. Therefore the conclusion based on this idea, that the construction of HE Ombla will have neutral to moderately positive effect on the target habitat is incorrect.
5. Due to the lack of year-round research, our understanding of bat fauna annual dynamics and usage of the Vilina cave is incomplete. In addition, key microclimate conditions that are important for the selection of roost and for well-being of maternity colonies and juveniles, have not been measured in all periods.
6. Both the construction and operation phase will cause degradation of the cave and the surrounding habitats. This will have negative impact on bat fauna and the prescribed mitigation measures will not reduce the impact to an acceptable level. Not all available literature about the subject was consulted and/or cited in the present study, and the conclusions indicate the lack of understanding of basic features of cave habitats.
8. The Vilina špilja - izvor Omble Cave System as well as caves in the wider area have not been adequately nor systematically explored. Recent researches, financed by the HEP (Croatian Electricity Company) were conducted in the period of only three months (March-June 2012 for the Cave System and August - November 2014 for all other caves in wider area). Moreover, the deepest flooded parts of the cave system were not explored at all and fauna of that part is unknown. However, the flooded underground passages are the core habitat for the two Nature 2000 species which have been recorded in Vilina špilja - izvor Omble Cave System previously but not in recent researches (Congeria kusceri and Proteus anguinus). The minimum needed period for systematic research is one year in order to cover all seasons and different water levels.
9. The Vilina špilja - izvor Omble Cave System has never been completely surveyed or mapped. Recent researches (2012) found unexplored passages of the cave system in the flooded parts and more should be expected in the deepest flooded parts of the cave.
10. In conclusion, the construction of the HE Ombla will have negative impacts both to the protected species and to cave habitat 8310 within Paleoombla - Ombla Site. Therefore we consider this intervention in nature unacceptable.