Not to be cited without prior reference to the authors Reaction norm analysis of fisheries-induced adaptive change and the case of the Northeast Arctic cod

• Main Authors: Mikko Heino, Ulf Dieckmann, Olav Rune Godø
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; Matu; Arctic cod; Northeast Arctic cod
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.573.356; http://www.bio.uib.no/evofish/papers/Heino_2002_Reaction_norm_analysis.pdf

We present a probabilistic concept of reaction norms for age and size at maturation, and out-line methods that can be used for their estimation in typical fisheries data. Such estimations are critical for calibrating size- and age-structured population models, for understanding phe-notypic plasticity and life-history changes in variable environments, and for assessing genetic changes in the presence of phenotypic plasticity. We apply the method of reaction norm esti-mation to a set of measurements on Northeast Arctic cod collected between 1932 and 1998. This cod stock has shown a drastic reduction in age at maturation. In the 1930’s, age at matu-ration was typically around 10-11 years, whereas nowadays seven years is more usual. This change has been attributed both to fisheries-induced genetic selection for earlier maturation, and to a compensatory response caused by faster individual growth rate. However, previous analyses have been unable to disentangle these hypotheses. Our analysis, based on estimation of maturation reaction norms, shows that both increase in growth rate and change in age- and size-specific tendency to mature have contributed to the observed trend towards earlier matu-ration. The latter component probably represents a fisheries-induced adaptive genetic change. Key words: evolution, fisheries-induced change, age and size at maturation, phenotypic plas-ticity, reaction norms.