The European Inland Fisheries Advisory Commission (EIFAC) felt the need to pay more attention to impacts on fishery resources by other users of water, such as traffic of pleasure boats and intensive recreation on lake shores. Recreational activities and the increased input of nitrogen and phosphorus were identified as the main cause of the reduction of the aquatic vegetation (EIFAC/CECPI 1984). Because the aquatic vegetation is an important part of the habitat of many fish species, EIFAC recommended a compilation of bibliography on the causes of the destruction of reeds and other aquatic vegetation and remedial measures for their restoration (recommendation 69.2 of Thirteenth Session in Aarhus, 1984).
This paper documents the decrease in aquatic plants in many water bodies in the temperate zone of Europe and North America. It also pays attention to control and management techniques to protect or restore the lake shore vegetation.
Although the relationship between the presence of aquatic vegetation and the well-being of fish is obvious, causal relations are poorly documented. The same is true for the damage to fish populations caused by the decline in aquatic vegetation. Moss et al. (1979) produced some evidence for a considerable decline in catches in the Norfolk Broads and Rivers (England) after a strong decrease in biomass and species composition of aquatic plants. Grosch (1978, 1980) reported strong negative effects on the species composition of the fish fauna in the Havel lakes (West-Berlin) because of the destruction of the aquatic vegetation. Oster (1980) (in Lake Ontario, Canada) and Price et al. (1985) (in the Chesapeake Bayt U.S.A.), mentioned dramatic effects on fish stocks because of eutrophication and changes in the aquatic vegetation.
During the last 10 years many studies have been carried out on the ecological significance of aquatic macrophytes for the whole ecosystem with emphasis on nutrient demand and release, and the relations with invertebrates. This paper reviews a number of conceptual models by which the effect of eutrophication on the aquatic vegetation, and indirectly the effect on fish, can be understood. These mechanisms of interaction are of great significance for habitat improvement techniques, which will be very important for the fish fauna.
