Fish sampling and individual data
The total number of sampled fish across the 11 lakes was nearly 60 000, of which 12 000 were perch, and the littoral catches from this data were used to describe the development in proportion of perch in the 11 lakes (Appendix Table S1, the fish community of the individual lakes are described in the Supplementary information). Fish were collected using multimesh gill-nets or gill net series in all three sampled habitats (i.e. littoral, pelagic, profundal) of the lakes, but only fish from the littoral zone were included in the analyses because the sampling in the other habitats was more scattered in both time and space (See supplementary information for details on the fish sampling procedure). We used individual data from the two lakes most frequently and intensively sampled (Lake Vaggatem and Lake Skrukkebukta), to assess changes in life history parameters over time in the perch populations. These two lakes were selected because of their long time series (~1991-2020) with mostly annual sampling, including daily data on water temperature, and detailed individual data collected from year 2003 to 2020. A total of 2960 individual perch from Lake Vaggatem (n=38-608 per year) and Lake Skrukkebukta (n=30-130) were sampled. The individual fish sampling procedure and summary information on individual- and population level data are described in the supplementary information Appendix 1 (see Tables S2 & S3).