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.