Talk Stream sections under road bridges as conservation hotspots of native crayfish and fish species

Most biological studies on linear infrastructures focus on fragmentation, road kills, invasion by exotic species, effect of air, noise and chemical pollution on animal behaviour or the effect of preventing measures. Relatively little attention is given to the habitat function of different types of streams and channels under the road, motorway and railway bridges. In the last decades the results of monitoring indicated that not only the ecological status of water bodies are changed negatively by human activities, but also the population of several native aquatic animals are substantially reduced in Hungary. Recently the researches have few information about the role of aquatic habitats in streams beneath and around bridges.

In 2013 a research program was started by MTA Centre for Ecological Research and Vox Vallis Development Association (managing organisation of Koppányvölgy Natúrpark in Somogy County). Crayfish and fish faunistical assemblages were surveyed by electrofishing once in each season beneath and around seven bridges of the Koppány-stream. Each sampling area is a section consisting the neighbouring upstream and downstream from the bridge as well, and the sampling sites were characterised by 11 environmental variables. Apart from the wastewater load there are intensive anthropogenic effects on the catchment area, most of all the diffuse contamination as the consequence of the intensive crop production, which imposes a considerable risk on the natural values of the stream and its tributaries. The presentation summarises results of three research seasons between 2013 and 2015.

One native crayfish species was presented by samplings. All of the 137 individuals could only be caught under the bridges, where the current velocity and sediment composition were optimal for them. A total of 3571 individuals of 29 fish species were caught, with 2031 individuals of 23 species being juveniles. Four of the species was non-native (Carassius gibelio, Neogobius fluviatilis Pseudorasbora parva, Lepomis gibbosus). The reophil cyprinid fish species (Alburnoides bipunctatus, Cobitis elongatoides, Gobio gobio komplex, Romanogobio vladykovi) were caught in the middle and upper section of Koppány stream only in the sampling sites at bridges, because the current velocity and the sediment composition were optimal at different water levels at these sections. The non-native and native eurytop species were represented equally in each section, but in summer, in the low water level period the abundance of each fish species were higher under the bridges. The results presented that aquatic habitats under bridges had key role in conservation of native reophil species composition in a modified stream.

freshwater habitats, stream ecology, bridge