Faster juvenile growth with higher summer water temperature
The overall trend for the juvenile perch was that annual length increment increased with summer water temperature and decreased with relative density of perch in both Lake Vaggatem and Lake Skrukkebukta (Fig. 4, Appendix Fig. S7-10). The combined length increment (mm·year-1) from age 1 to age 4 year old perch increased substantially with increasing 3-year-mean summer water temperature and decreased similarly with an increase in 3-year-mean relative density (Fig. 5a & 5b). The combined length increment (age 1 to 4 year) for Lake Vaggatem and Lake Skrukkebukta perch was significantly related to temperature and density in a linear regression model (p=0.004, adj-R2=0.28), increasing by 8.5 mm per degree centigrade of temperature increment (t=2.481 on 31 d.f., p=0.019) and decreased by 6.8 mm per 10 CPUE increment (t=-3.806 on 31 d.f., p=0.001) (Appendix Table S16). In addition, there was a difference in intercept between the lakes, where the length increment was larger in Lake Vaggatem compared to Lake Skrukkebukta (Appendix Table S16). However, for the individual age groups, the effect of water temperature and relative density on length increment varied. For the youngest age group (1 year old) there was no significant change in length increment (mm·year-1) with either increasing summer water temperature or relative density of perch (Fig. 4, Appendix: Fig. S7, Table S17 & S18). For all the other juvenile age groups (2 to 4 year old), length increment (mm·year-1) increased significantly with increasing summer water temperature in both lakes, whereas only in Lake Vaggatem length increment decreased significantly with relative density of perch (Fig. 4, Appendix: Fig. S6-S10, Table S19-S24) (See Supplementary information for more detailed description of results).