Aquatic macrophyte vegetation and its relationship to the occurrence of the Eurasian Otter in the Hron river

 

As the top predator of the trophic water chain, the Eurasian otter (Lutra lutra Linnaeus, 1758) has an important position as an keystone, umbrella and focus species of any given water ecosystems. The main ecological factor, which affects its presence in water biotopes, is sufficient food supply (e.g. Kruuk, 1995, 2006; Jendrzejewska et al., 2001; Clavero et al., 2003). Other factors such as lack of shelter have a significantly smaller influence, but, however, vegetation in the broad sense seems to be frequently studied (O’Connor et al., 1977; Jenkins and Burrows, 1980; Macdonald and Mason, 1983; Bass et al., 1984). Some studies based on spraints have pointed to the importance of the presence of trees, woodland or other cover, as well as the impact of human activities, while others have also demonstrated a relationship with food supply (Macdonald and Mason, 1983; Bas et al., 1984; Prenda and Granado-Lorencio, 1996; Chanin, 2003). Some authors observed a positive correlation between the amount of bank vegetation cover and sprainting activity over large areas (Adrián et al., 1985; MacDonald and Mason, 1985; Delibes et al., 1991; Prenda and Granado-Lorencio, 1996).

The relationship between the presence of the otter, expressed by otter sign behaviour, and the qualitative characteristics of aquatic macrophytes is a scarcely investigated topic. We believe that, due to the strong influence of food availability, otters could show a preference for visiting sections with higher qualitative and quantitative representation of macrophytes in the Hron River. It is well known that submerged macrophytes add to the physical complexity of the environment, creating habitat that algae and invertebrates may colonize and providing refuge for fishes from high flows and predators (Allan and Castillo, 2007). Therefore the sections with richer species composition and with more or less similar or greater cover of macrophytes, are more diverse and more representative of the preferred food of the otter.

The aim of this article is to examine the natural habitat of the Hron River to find out whether i) parts of the river can be classified by species composition of macrophytes, and consequently ii) to find out if the quantity of otter signs differs within various parts of the river based on the various macrophytes present.