CHANGES IN THE INLAND FISH POPULATIONS IN EUROPE IN RELATION TO THE INCREASE OF THE CORMORANT PHALACROCORAX-CARBO-SINENSIS

Fish populations in Europe react on increasing eutrophication in a gen eral pattern. However this pattern is locally different and strongly d epends on the 'natural', pre-eutrophicated situation. The general tren d is toward unstable fish populations with dominance of small, short l iving, early maturing fish like Perch Perca fluviatilis, Ruffe Gymnoce phalus cernuus, Smelt Osmerus eperlanus and/or carp-like fish (cyprini ds) mainly Roach Rutilus rutilus and Bream Abramis brama. The high-bod ied Bream is negatively selected for by Cormorants in favour of Roach, Perch, Ruffe or Smelt. Social fishing on shoaling young fish of speci es like Perch, Ruffe, Smelt and Roach in relatively turbid, eutrophic lakes with few submerged water vegetation can be considered as an adap tation of the inland breeding population of Cormorants to eutrophicati on caused by human activity. Where lakes and rivers are still clear an d relatively unpolluted, the Cormorant returns to its habit as solitar y hunter, predating on Eel Anguilla anguilla, Trout Salmo trutta or cy prinid species of running waters like Chub Leuciscus cephalus.