Vast amounts of individual data are collected annually for monitoring and assessment of commercially important fish stocks.These data are a valuable source of information for studies that extend far beyond the original goals of data collection.

An interesting question for EvoFish is whether we can detect signs of fisheries-induced evolution in fish data. The challenge is that outside controlled environments, phenotypic data alone cannot prove evolutionary (i.e., genetic change). Change in phenotypic population characteristics is influenced by population demography and phenotypic plasticity. These can never be fully disentangled from genetic-based changes, but their influence can nevertheless be reduced. A useful tool for this is the probabilistic maturation reaction norm analysis we have been developing over the years. The approach has been used by us and many others to study maturation trends in numerous fish stocks all over the world.

Probabilistic maturation reaction norms (PMRN) were originally introduced by Heino, Dieckmann & Godø (2002). A general discussion about their strengths and limitations was presented by Dieckmann & Heino (2007), and a general overview of the approach is presented by Heino & Dieckmann (2008).