L. Forró szerk.: Miscellanea Zoologica Hungarica 10. 1995 (Budapest, 1995)

Kappus, B., Jansen, W. , Fok, P.; Rahmann, H.: Threatened lamprey (Lampetra planeri) populations of the Danube Basin within Baden-Württemberg, Germany

MISCELLANEA ZOOLOGICA HUNGARICA Tomus 10. 1995 p. 85-98 Threatened lamprey (Lampetra planeri) populations of the Danube Basin within BadenWürttemberg, Germany by B. Kappus, W. Jansen, P. Fok, and H. Rahmann (Received March 22, 1995) Abstract: The brook lamprey (Lampetra planeri) populations of the upper Danube Basin within BadenWürttemberg (Germany) were studied between 1989 and 1994. Ten recently extinct and 40 currently existing populations were documented and major factors threatening their existence were identified. Among these factors, physical obstacles forming effective migration barriers often confine populations to isolated reaches of a river without the possibility of (genetic) exchange with other populations further downstream or within the Danube itself. Further physical disturbances adversely affecting lamprey habitat include river channelization, river bank reconstruction and sediment removal. As evidenced in the Laudiert River, sediment removal was the direct cause of mortality for substantial numbers of lampreys. The contamination of waters with organic wastes from agricultural use, input of nutrients from diffuse run-off or point sources, such as water treatment plants, and accidental toxic spills are generally of less importance, nevertheless represent significant threats for individual lamprey populations. Finally, heavy stocking of catchable size salmonids, particularly in unsuitable rivers, can lead to increased prédation pressure on adult lampreys and, therefore, reduced population fecundity. The relative importance of the different factors that put lamprey populations at risk are quantified and discussed in the context of feasible conservation measures. Key words: brook lamprey, Lampetra planeri, habitat alteration, water quality, population extinction, upper Danube Basin Introduction Lampreys are sediment dwellers. The larvae, usually termed ammocoetes, spend 6 to 8 years hidden in the sediments of running waters where they filter organic particles (Hardisty & Potter 1971). Unlike the predatory, marine species, as for example the sea lamprey (Petromyzon inarinus) and the river lamprey (Lampetra fluviatilis), which can migrate considerable distances back to the ocean after metamorphosis, the limnetic forms are stationary and complete their whole life-cycle in their native area (Holcik 1986). Among these latter species are the brook lamprey (Lampetra planeri), the Danube brook lamprey (Eudontomyzon mariae) and the Danube lamprey (Eudontomyzon danfordi), which is also predatory. As their names indicate, the centre of distribution of the two latter species is the Danube Basin, where E. danfordi is particularly limited to the Hungarian Tisza area (Banarescu 1969, Renaud 1982). All of the lamprey species occurring in Central Europe, both anadromous and stationary, are considered threatened and have been included in the "Red List" of endangered animal species in Europe (Lelek 1987). The brook lamprey (L. planeri) has been classified as "strongly endangered" throughout its European range and is listed as a "protected species" in the species protection agreements of the European Council (ER 1988). Within Germany, L.