Figure 6. a) Structural equation model showing the relationship between predictor variables affecting length increment (combined from age 1 year to age 4 year olds) and the effect of increasing length increment on age at maturation in the perch populations in Lake Vaggatem and Lake Skrukkebukta. Arrows represent causal pathways, highlighted black lines represent significant relationships and grey lines represent non-significant relationship within the model. Numbers in boxes denote the effect size of standardized coefficients and R2 is shown for each endogenous variable. b) Relationship between somatic growth and maturation in perch in the Pasvik watercourse illustrated by the maturation reaction norm, length at age for perch in the Pasvik watercourse (grey dots) with blue dotted line representing a slow growth rate, i.e. “cold and high density situation” (10th percentile) and orange dotted line representing a fast growth rate, i.e. “warm and low density situation” (90th percentile). The population estimated probabilistic maturation reaction norm (PMRN) midpoint (solid line), the 25th and 75th percentile (dashed lines).