Earlier maturation age with faster growth
Age at maturation (A50) differed between males and females in the perch populations in Lake Vaggatem and Lake Skrukkebukta; males matured on average at an age of 4.1 years whereas females matured on average at an age of 7.5 years (Appendix Fig. S11). The difference in age at maturity between the sexes did not change over time (t=-0.767 on 12 d.f., p=0.45) (Appendix Fig. S12). The observed increase in combined length increment (mm·1-4years-1) substantially affected the cohort specific age at maturation (A50) negatively (Fig. 5c), with -0.8 years reduction per cm increase in length increment (t=-3.783 on 14 d.f., p=0.002, adj-R2=0.47) (Appendix Table S25 & Fig. S13). The effect of summer water temperature and relative density on age at maturity was mediated through growth (length increment) for perch in Lake Vaggatem and Lake Skrukkebukta, as illustrated by the structural equation model (SEM) results (Fig 6a). We found a positive effect of cohort-specific (age 1 to age 4 year old) mean summer water temperature and a negative effect of relative density of perch in the same time period on length increment of perch from age 1 to age 4 year, which further affected age at maturity (A50) negatively (Fig. 6a). Figure 6b illustrates these relationships theoretically, where individuals with higher growth rate, due to temperature increase or reduced density, will reach maturation age earlier than populations experiencing lower growth rates according to the estimated PMRN from the perch populations in Lake Vaggatem and Lake Skrukkebukta.