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
6 -r 5 4 3 1 stocking intensity Fig. 4. Absolute number (n) of different combinations in the level of stocking intensity (high = introduction of adult sized trout several times a year; low = introduction of fry or fingcrlings once a year; none = no stocking) and lamprey population density (levels of low, intermediate, and high densities were assigned subjectively base on sampling by electro-fishing, nets, and observations at the site). A total of 33 lamprey populations were considered stocked and lamprey population size (Fig. 4). However, the lack of a general relationship must be considered with caution, because stocking practices differed with regard to the size of the fish stocked. Whereas fingerling trout do not put lampreys at risk, stocking of adult size trout can exert an adverse effect on lamprey populations. For example, direct observations of lamprey-salmonid interactions during each of the reproductive seasons 1991-1993 at the River Schmiech confirmed that trout (Salmo trutta and Oncorhynchus mykiss) aggregated in the vicinity of lamprey spawning sites and frequently preyed upon mature individuals. Therefore, intensive stocking with adult-size salmonids (S. trutta, O. mykiss and Salvelinus fontinalis), particularly into unsuitable water bodies, may contribute to the reduction of lamprey populations (and of other endemic small fish species). Not only stocking with adult size salmonids, but also with fry may be harmful to lamprey populations. Frequently salmonid fry are stocked into very small creeks only to be recaptured months later as fingerlings by electro-fishing. If a lamprey population is present in such a habitat, this method of capture, if not carried out carefully, may harm or even kill ammocoetes. Finally, the large scale stocking of eels (Anguilla anguilla) must be considered detrimental to the autochthonous lamprey populations, because lampreys of unknown origin and species are frequently found with the introduced eels. In order to obtain an estimate of the numbers involved, authorities at the German Fisheries Association (Deutscher Fischerei Verband), responsible for the shipping of eels used for stocking, were approached. The information obtained indicated that among the eels, river lampreys (L. fluviatilis) are found in quantities of "less than 1%" and that the "percentage has been declining in recent years".
