Effect of sports fisherman activities on dragonfly assemblages on a Hungarian river floodplain.

We studied the dragonfly fauna along a 15 km stretch of thefloodplain of the regulated, first-order river Tisza, Hungary. Data on capturedand observed adults, larvae and exuvia were recorded. Observations were madefrom May to October 1998 and 1999 on 34 species, which is 52% of theHungarian fauna. Classification on the basis of faunistic similarity revealedthat habitat-level differences, associated with various degrees of physicalanthropogenic impact on bank vegetation, can exceed variation among the waterbodies of different types (backwater, pond, marsh, canal, river). The richestsites were dominated by structurally diverse macrophyte vegetation, while flowing waters (river and canal) were poorest in species. Odonata were found tobe reliable indicators of small-scale habitat patterns, reflecting vegetationdifferences even within single water bodies where the sampling spots werearranged just a few hundred metres apart. Along a gradient of utilisationintensity, the species number of Odonata assemblages and the summed relativeabundance of the five rarest species of the study area decreased linearly withincreasing fragmentation of the marginal vegetation. Sports fishermanactivities, implying disruption of the littoral marsh zone by establishment ofclearings and excessive trampling of the banks, can also be monitored bydragonfly faunistic investigations. Our results demonstrate that conservation ofthese varied floodplain water bodies requires the control of sports fishingactivity, suggesting that (i) to maintain the representative odonate fauna ofthe water bodies, some non-fragmented shores must be provided; and (ii) permanentfishing stands should not exceed 8 m mean width and should beseparated by at least 12 m of intact riparian sections.