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Research article - Peer-reviewed, 2001

Intercohort competition effects on survival, movement, and growth of brown trout (Salmo trutta) in Swedish streams

Nordwall, Fredrik; Näslund, Ingemar; Degerman, Erik


The effects of density-dependent intercohort competition on growth and mortality in stream-resident brown trout (Salmo trutta) were tested by experimentally reducing the densities of age-1 fish and fish older than age 1 in six small streams. When densities of age-1 fish were reduced, abundance of age-0 and age-1 fish increased the following year, while age-1 fish experienced a reduced mean size. Reduced densities of fish older than age 1 resulted in increased apparent survival of age-0, age-1, and age-2 fish in the subsequent year. Mean size of age-2 fish increased as well. Many older immigrants (age >2) were found in the treatment sections where densities previously had been reduced. Data from the Swedish Electrofishing RegiSter (SERS) showed that mean body size of age-0 brown trout was negatively related to both age-0 and age >0 densities. The database also verified the inverse relationship between age-0 abundance and abundance of older cohorts. Our results indicate that intercohort competition regulates territorial fish populations, even when simple single populations in restricted environments are considered.

Published in

Canadian Journal of Fisheries and Aquatic Sciences
2001, Volume: 58, number: 11, pages: 2298-2308

    SLU Authors

    • Nordwall, Fredrik

      • Department of Aquaculture, Swedish University of Agricultural Sciences
      • Degerman, Erik

        • Swedish Board of Fisheries

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