Recent studies have drawn attention to the potential for evolutionary changes in lifehistory 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 450: 147-157, 2012 ated with reproduction, such as (1) competition for resources required for reproduction, e.g. competition for mates or nest sites; (2) the amount of space within the body cavity that can be allocated to reproductive organs; and (3) the costs of locomotion. In all 3 instances, individuals that become reproductive at a larger size might be expected to have a reduced sizespecific cost of reproduction. A life-history strategy of delayed maturation allowing for increased growth might therefore be considered optimal in terms of maximising reproductive potential, but this must be offset against competing processes such as the predation risk of foraging that might favour an alternative strategy of reduced growth and earlier maturation (Mangel & Stamps 2001). A trade-off therefore exists in the adoption of specific life-history traits that maximise reproductive potential given the competing objectives of increased growth, reduced mortality and reproductive investment. The age at which first maturity occurs is a reflection of the strategic approach that a given species takes to this trade-off and will be highly correlated with other life-history traits, such as growth rate and maximum size.
Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerA number of 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 (Rijnsdorp 1993, Law 2000, Heino et al. 2002a, and evidence of so-called fisheries-induce...