Patterns in water quality and fish status of some acidified lads in southern Finland during a decade: Recovery proceeding

Since the early 1980s, the acidic deposition in the northern Europe has dec reased substantially. This has resulted in corresponding improvements of th e water quality in some acid sensitive small lakes of southern Finland. Amo ng the fish of these lakes, the first signs of recovery were recorded in th e early 1990s, when the European perch (Perca fluviatilis L.) started to re produce in some sparse populations. Since then, the reproduction of perch h as been successful in several years. The appearance of strong year-classes in lakes earlier almost empty of fish indicates recovery. This development has resulted in increased population densities, decreased mean sizes of fis h and decreased growth rates. In a more acid sensitive species, roach (Ruti lus rutilus (L.)), no clear indications of recovery have been recorded this far. However, schools of small roach (age 1+) were observed in the summer of 1998 in two acidic lakes that were inhabited by sparse roach populations during 1985-1995.