Estimating age at first maturity in fish from change-points in growth rate

Abstract

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...

Accurate estimates of age at maturity from the growth trajectories of fishes and other ectotherms

“…If the LM can be fit to length at age data without estimates of AAM, then it could be a powerful tool for estimating life history traits from contemporary and historical samples. Previous attempts to estimate AAM from growth data using breakpoint linear regressions (Rijnsdorp and Storbeck , Baulier and Heino , Scott and Heikkonen ), modified forms of the VBGM (Ohnishi et al. ), biphasic growth models (Mollet et al.…”

Mixed-Effects Modelling of Scale Growth Profiles Predicts the Occurrence of Early and Late Fish Migrants

“…In addition, growth is intimately linked to many life history traits [13], and cannot be considered in isolation. For example, rate of growth has a pervasive effect on age at maturity in fishes [14]–[16], and on longevity in mammals [17].…”

Estimating age at maturation and energy-based life-history traits from individual growth trajectories with nonlinear mixed-effects models

“…This method was applied recently to Irish Sea plaice (Scott and Heikkonen 2012) and to NSSH (Baulier and Heino 2008). In NSSH, a 47.6 % agreement between the 'breakpoint' estimates of age at maturation and those read from scale marks was obtained, with the highest disagreement found for latematuring individuals.…”

“…Firstly, maturity ogives can be calculated from the estimated mean and variance of age at maturation in each cohort. In the context of fish stock assessment, for instance, this provides an alternative to the traditional estimation of maturity ogives based on the determination of fish maturity stage by visual inspection of the gonads, which is potentially affected by various sources of errors (see also Scott and Heikkonen 2012). Moreover, for many fish stocks, maturity data are too scarce to estimate a maturity ogive for each cohort, so that temporal variations in maturity cannot be accounted for.…”