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

truckloads full of sediments (80% sand, 20% organic compounds) were deposited 500 m away from the removal site. Inspection of the sediments, both on the trucks and at the dump site revealed a total of approximately 700 animals, mainly ammocoetes, which were effectively removed from their habitat and killed. Most of the larvae were found in the organic laden sediments, less so in the sediments consisting of almost pure sands. Considering that the young larvae (ca. 30 mm) were very difficult to detect within the sediments, the total loss of lampreys was estimated to be at least 1500 animals. The remaining sediments left in the river were also inspected and approximately 100 lampreys were found within half an hour of searching. Among these, 20 subadult "macrophthalmia" (i.e. animals that will spawn in spring) were identified, readily distinguishable by their prominent eyes. Input of toxicants and nutrients Unfortunately, the accidental introduction of toxicants into rivers occasionally still occurs. Two such "accidents" were recorded during the present study and had severe effects on the lamprey populations. In August of 1991, cyanide from the water treatment plant at Peterzell resulted in a massive fish kill which affected a 15 km long section of the Brigach River. Although no dead or dying lampreys were reported by local fishermen who were mainly observing the moribund salmonids and cyprinids, there was indirect evidence that lampreys were also affected by the cyanide. One day after the spill, an electro-fishing survey showed the complete absence of lampreys in the affected area, while immediately upstream, within the city limits of St. Georgen, lampreys were present. A second case of river pollution was documented in 1989 when mineral oil entered the Wolfbach at Rietheim, which was certain to have adverse effects on the lamprey population. In addition to these known toxic spills, and nutrient input from point sources such as sewer outfalls or water treatment plants, organic wastes from agricultural sources may enter the rivers as diffuse run-off from fields. Occasionally, larger amounts of raw sewage are illegally "disposed of by directly emptying containers onto frozen fields close to rivers. Such an incidence where large amounts of raw sewage entered the Wolfbach at Rietheim, was witnessed in February 1992. Water acidification must be considered as another source of chemical "contamination" of lamprey habitats. During this study it was found that the creeks flowing through the red sandstone bedrock at Villingen-Schwenningen had increased water acidity with yearly mean pH values of 6,6 (WarenbachTWieselsbach). As evidenced by the relatively large and stable population of the Warenbach, this depression in water pH does not, as yet, seem to be critical for the successful reproduction of the brook lamprey. Fisheries practices The intensive management of many rivers for sport fishing purposes represents a further, although limited, threat to lamprey populations. Of the 33 river sections with known lamprey populations that were managed for sport fishing purposes, only 12% were intensively stocked, i.e. adult size salmonids were introduced into the river several times a year. Forty five percent of these sites were stocked at low intensity and 42% were not stocked at all. Low intensity stocking represents introduction of fry and fingerlings once a year. Although just one case could be established in which high lamprey population density occurred concomitant with high stocking intensity, there was no general negative correlation between the number of salmonids