MEPS 450:147-157 (2012)  -  DOI: https://doi.org/10.3354/meps09565

ABSTRACT: Recent studies have drawn attention to the potential for evolutionary changes in life-history traits as a consequence of the size-selective process of fishing, and evidence of so-called fisheries-induced evolution has been reported for a number of different species. Most studies of fisheries-induced evolution have focused on changes in sexual maturation using the probabilistic maturation reaction norm method, which requires specific information on the age at which maturation occurs, often derived from macroscopic examination of the gonads. In the absence of sufficiently detailed measurements of maturity it is necessary to derive estimates of the age at which maturation occurs from alternative sources of information, for example, from length at age data. We apply a relatively simple segmented regression model to length at age data for plaice Pleuronectes platessa in the Irish Sea in order to identify the change-point between 2 specific growth schedules that can be used as a proxy for age at first maturity in individual cohorts. We use a Bayesian approach for model fitting and map the resulting distribution of change-points using Gaussian mixture models to show that the age at which the change-point occurred in individual cohorts of both male and female plaice in the Irish Sea has declined progressively over an 18 yr period between 1988 and 2005.

KEY WORDS: Plaice · Maturation · Segmented regression · Reaction norm · Genetic adaptation · Phenotypic plasticity