Ábrahám Levente: Biomonitoring a Dráva folyó magyarországi szakasza mentén 2000-2004 - Natura Somogyiensis 7. (Kaposvár, 2005)

Lanszki József: Otter monitoring between 2000 and 2004 in the Drava region (Hungary) - A vidra monitorozás 2000 és 2004 között a Dráva mentén

Natura Somogyiensis 7 169-178 Kaposvár, 2005 Otter monitoring between 2000 and 2004 in the Drava region (Hungary) LANSZKI JÓZSEF University of Kaposvár, Ecological Research Group, H-7401 Kaposvár, P.O. Box 16, Hungary, lanszki@mail.atk.u-kaposvar.hu LANSZKI J: Otter monitoring between 2000 and 2004 in the Drava region (Hungary). Abstract: The monitoring of the strictly protected Eurasian otter (Lutra lutra) started during the winter of 2000, in the Danube-Drava National Park, along the Drava River (between Őrtilos and Bares). The relative density of otters was surveyed by spraint counts along a standard route (line transect survey). The highest otter spraint density was measured at Bélavár (on Drava and backwater), and relatively high values were also found on ponds where the human disturbance was low. On the Dráva River, the mean relative density was moderate, which may be associated with the high fluctuations of water levels and the steep riverside. Otter density was lower on gravel-pit lakes and backwaters with intensive angling, as well as on watercourses and streams in connection with the Dráva River. From 2002 the monitoring was completed by genetic analysis (using nine DNA markers) from freshly collected spraints. The results of the diet composition examined by spraint analysis are also summarized. It can be concluded on the basis of the above findings that the otters' population sensitively reflects the changes of the habitats, preservation of the riverside vegetation and that of the landscape. Key-words: Lutra lutra, Drava River, backwater, relative density, diet Introduction The Eurasian otter Lutra lutra (Linnaeus, 1758) is a widely occurring predator in Europe, living in a large variety of watery habitats (MASON and MACDONALD 1986, KRUUK 1995, KRANZ 2000, CONROY and CHANIN 2002). The species shows continuous presence in all the habitats along the Drava River (HELTAI et al. 2004), which is one of the least artificially modified rivers in Central Europe, being rich in natural habitats. All sections of the river are included in the Danube-Drava National Park (IVÁNYI and LEHMANN 2002). Monitoring of the strictly protected and threatened otter started in year 2000 on the Drava River and on connecting watery habitats, after planning a high-capacity hydroelectric power station on the river in the region Novo Virje. Otter numbers are limited by fish populations (reviewed by KRUUK 1995), and feeding behaviour is dependent on the available food supply (ERLINGE 1967, 1969, WISE et al. 1981, KRUUK and MOORHOUSE 1990, KRUUK et al. 1991, CARSS 1995, RUIZ-OLMO et al. 2001). In addition to the abundance of available food, other factors affecting occurrence and feeding habits are type of habitats, quality of bankside, steepness of waterside banks and the degree of human influence to which the area is exposed (ERLINGE 1967, KEMENES and DEMETER 1995, JEDRZEJEWSKA et al. 2001, RUIZ-OLMO et al. 2001, LANSZKI 2002, RUIZ-OLMO et al. 2002, CLAVERO et al. 2003).