Tillväxt av öring (Salmo trutta) i bastuån : Täthets- och temperaturberoende?

Sammanfattning: Performance of stream living juvenile brown trout (Salmo trutta) may be affected by both intra- and intercohort competition. In this study I examined if growth and density of cohorts of young-of the-year (0+) trout are dependent on temperature and density of older (>0+) trout and 0+ trout. Data on growth and densities were obtained using a long time series of quantitative electrofishing data from 1998 to - 2020 on size and densities of cohorts of trout from three sites in the stream Bastuån, Jämtland Sweden. The growth was defined as the length of 0+ in the end of august and densities were based on the three-removal method and area of the stream site. The growth of 0+ trout was not affected negatively by the density of >0+ trout or by the density of 0+ trout. On the other hand, increasing temperature had a positive effect on the growth of 0+ trout. The results suggest that temperature in the temperature range experienced by 0+ trout in this study is the main driver of growth of 0+ trout while density dependent growth is not a general pattern in this natural trout stream. Continuous sampling to expand the time series in Bastuån are recommended to allow for further studies of the factors behind growth and densities of juvenile trout especially when considering future expected climate change effects on water temperatures.