The fish communities in and the trophic states of lakes Mälaren and Hjälmaren have changed gradually since the late 1700s. In both lakes, pikeperch (Stizostedion lucioperca), Eurasian perch (Perca fluviatilis), and northern pike (Esox lucius) are important species in the recreational and commercial fishery. Pikeperch has increased from an unimportant species to predominance in both lakes. The importance of Eurasian perch however, has decreased markedly. The most likely explanation for these changes is increased cultural eutrophication.
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Hugo Rundberg (1977) studied this question.
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