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Population Density of Brown Trout (Salmo trutta) in Extremely Dilute Water Qualities in Mountain Lakes in Southwestern Norway


We have examined populations of brown trout in low-conductivity mountain lakes (5.0–13.7 μS/cm and 0.14–0.41 mg/l Ca) in southwestern Norway during the period 2000–2010. Inlets to the lakes were occasionally even more dilute (2007; conductivity = 2.9–4.8 μS/cm and Ca = 0.06–0.17 mg/l). The combination of pH and conductivity was the best predictor to fish status (CPUE), indicating that availability of essential ions was the primary restricting factor to fish populations in these extremely diluted water qualities. We suggest that conductivity <5 μS/cm is detrimental to early life stages of brown trout, and subsequently that there are lakes in these mountains having too low conductivity to support self-reproducing trout populations. Limited significance of alkalinity, Ca, Al, and color suggests that effects of ion deficit apparently overruled the effects of other parameters.

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The authors thank Dr Richard F. Wright for valuable comments to this paper, Associate Professor Bjørn Auestad for performing the regression analysis, and Tom Arild Homme for testfishing 3 of the lakes. The registrations of fish and water chemistry were financed by Sira-Kvina Power Company (n = 24) and the County Governor of Aust-Agder (n = 1).

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Correspondence to Frode Kroglund.



Table 7 Fish and water chemical data from mountain lakes in southwestern Norway

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Enge, E., Kroglund, F. Population Density of Brown Trout (Salmo trutta) in Extremely Dilute Water Qualities in Mountain Lakes in Southwestern Norway. Water Air Soil Pollut 219, 489–499 (2011). https://doi.org/10.1007/s11270-010-0722-4

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  • Brown trout
  • Mountain lakes
  • pH
  • Conductivity