Epsilon Archive for Student Projects

Abstract

Brown trout, Salmo trutta, is an important species for the sportfishing tourism in Sweden
and goals are set high for the possible gains to come from fishing tourism. Therefore
accurate and efficient methods to estimate a streams potential production of brown trout are
needed in order to apply relevant management regimes that take fish ecology into account
and prevents overfishing. One measure of brown trout production is the density of young of
the year fish. The usual method for estimation of young of the year brown trout density are
electrofishing with three removals. In this study a method using environmental factors to
estimate maximum production of young of the year brown trout, as a measure of carrying
capacity, was used. Based on previous studies environmental factors important for brown
trout habitat requirement were selected. Data of stream slope, water flow, annual air
temperature, longest period above 0 °C, altitude, stream width and water depth were linked
to data on young of the year densities in a cluster analysis. The percentage relative
precision values for the estimated mean maximum densities showed a lower level of
uncertainty for density estimates based on environmental factors and cluster analysis than
for estimates based on electrofishing with three removals. An additional benefit of the use
of environmental data for estimations of maximum young of the year brown trout density is
that estimates can easier be scaled up to cover a whole stream without the use of long time
series of data. As opposed to estimation of brown trout production capacity for a whole
stream using electrofishing data which for reliable estimates require over time data (e.g. 10-
15 years).