Heino, M., Baulier, L., Boukal, D. S., Ernande, B., Johnston, F. D., Mollet, F. M., Pardoe, H., Therkildsen, N. O., Uusi-Heikkilä, S., Vainikka, A., Arlinghaus, R., Dankel, D. J., Dunlop, E. S., Eikeset, A. M., Enberg, K., Engelhard G. H., Jørgensen, C., Laugen, A. T., Matsumura, S., Nusslé, S., Urbach, D., Whitlock, R., Rijnsdorp, A. D., and Dieckmann, U. 2013. Can fisheries-induced evolution shift reference points for fisheries management? – ICES Journal of Marine Science, 70: 707–721. Biological reference points are important tools for fisheries management. Reference points are not static, but may change when a population's environment or the population itself changes. Fisheries-induced evolution is one mechanism that can alter population characteristics, leading to “shifting” reference points by modifying the underlying biological processes or by changing the perception of a fishery system. The former causes changes in “true” reference points, whereas the latter is caused by changes in the yardsticks used to quantify a system's status. Unaccounted shifts of either kind imply that reference points gradually lose their intended meaning. This can lead to increased precaution, which is safe, but potentially costly. Shifts can also occur in more perilous directions, such that actual risks are greater than anticipated. Our qualitative analysis suggests that all commonly used reference points are susceptible to shifting through fisheries-induced evolution, including the limit and “precautionary” reference points for spawning-stock biomass, Blim and Bpa, and the target reference point for fishing mortality, F0.1. Our findings call for increased awareness of fisheries-induced changes and highlight the value of always basing reference points on adequately updated information, to capture all changes in the biological processes that drive fish population dynamics.

Age and size at maturation decreased in several commercially exploited fish stocks, which, according to life history theory, may be due to fisheries-induced evolutionary change. However, the observed changes may also represent a plastic response to environmental variability. To disentangle phenotypic plasticity from evolutionary change, the probabilistic reaction norm approach was applied to 43 cohorts (1960 to 2002) of female sole Solea solea from market samples. The reaction norm for age and size at first maturation has significantly shifted towards younger age and smaller size. Size at 50% probability of maturation at Age 3 decreased from 28.6 cm (251 g) to 24.6 cm (128 g). This change was even stronger when condition was included as a third dimension in the reaction norm estimation. The influence of alternative factors was tested on the population level by regression of reaction norm midpoints on annual estimates of condition, temperature and competitive biomass. Although effects of temperature and competitive biomass were significant, the variation in the midpoints was best explained by the decreasing time trend. Therefore, the results provide strong evidence for a fisheries-induced evolutionary change in the onset of sexual maturity.

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We present a new methodology to estimate rates of energy acquisition, maintenance, reproductive investment and the onset of maturation (four-trait estimation) by fitting an energy allocation model to individual growth trajectories. The accuracy and precision of the method is evaluated on simulated growth trajectories. In the deterministic case, all life history parameters are well estimated with negligible bias over realistic parameter ranges. Adding environmental variability reduces precision, causes the maintenance and reproductive investment to be confounded with a negative error correlation, and tends, if strong, to result in an underestimation of the energy acquisition and maintenance and an overestimation of the age and size at the onset of maturation. Assuming a priori incorrect allometric scaling exponents also leads to a general but fairly predictable bias. To avoid confounding in applications we propose to assume a constant maintenance (three-trait estimation), which can be obtained by fitting reproductive investment simultaneously to size at age on population data. The results become qualitatively more robust but the improvement of the estimate of the onset of maturation is not significant. When applied to growth curves back-calculated from otoliths of female North Sea plaice Pleuronectes platessa, the four-trait and three-trait estimation produced estimates for the onset of maturation very similar to those obtained by direct observation. The correlations between life-history traits match expectations. We discuss the potential of the methodology in studies of the ecology and evolution of life history parameters in wild populations.

There is growing evidence that fishing causes evolution in life-history traits that affect the productivity of fish stocks. Here we explore the impact of fisheries-induced evolution (FIE) on the productivity of North Sea plaice (Pleuronectes platessa) using an ecogenetic, individual-based model by comparing management scenarios with and without an evolutionary response. Under status-quo management, plaice evolve towards smaller size at age, earlier maturation, and higher reproductive investment. Current reference points of maximum sustainable yield (MSY) and corresponding fishing-mortality rate (F MSY ) that ignore FIE will decrease and cannot be considered sustainable. The nature and extent of the change through FIE depend on fishing effort and selectivity. The adverse evolutionary effects can be reduced -and even reversed -by implementing a dome-shaped exploitation pattern protecting the large fish. The evolutionarily sustainable maximum yield can be obtained by combining such a dome-shaped exploitation pattern with a reduction in fishing mortality and an increase in mesh size; it is similar to the MSY that would apply if life-history traits were static. Fisheries managers will need to trade off the short-term loss in yield associated with evolutionarily informed management with the long-term loss in yield FIE causes under evolutionarily uninformed management.Résumé : Il apparaît de plus en plus clair que la pêche causerait l'évolution de caractères du cycle biologique qui ont une incidence sur la productivité des stocks de poi ssons. Nous examinons l'incidence de l'évolution induite par la pêche (EIP) sur la pr oductivité des plies (Pleuronectes platessa) de la mer du Nord à l'aide d'un modèle écogénétique basé sur l'individu, en comparant des scénarios de gestion avec et sans réaction évol utive. Dans une gestion en mode statu quo, les plies évoluent vers de plus faibles tailles selon l'âge, une maturation plus pr écoce et un investissement accru dans la reproduction. Les points de référence actuels du rendement équilibré maximal (REM) et du taux de mortalité par pêche correspondant (F REM ) qui ne tiennent pas compte de l'EIP sont appelés à diminuer et ne peuvent être considérés comme durables. La nature et l'ampleur des changements découlant de l'EIP dépendent de l'effort de pêche et de sa sélectivité. Les effets a dverses sur l'évolution peuvent être réduits, voire inversés, en appliquant une courbe d'exploitation en forme de dôme, qui protège les poissons de grande taille. Le REM durable au vu de l'évolution peut être obtenu en combinant une telle courbe d'exploitation à une réduction de la mortalité par pêche et une augmentation de la taille des mailles des filets; ce rendement est semblable au rendement équil ibré maximal qui s'appliquerait si les caractères du cycle biologique étaient statiques. Les gestionnaires des pêches devront soupeser les conséquences relatives de la réduction du rendement à court terme associée à une ge stion tenant compte de l'évolution et de la réduction du rendemen...

A new method is presented to estimate individuals' (1) age at maturation, (2) energy acquisition rate, (3) energy expenditure for body maintenance, and (4) reproductive investment, and the multivariate distribution of these traits in a population. The method relies on adjusting a conceptual energy allocation model to individual growth curves using nonlinear mixed-effects modelling. The method's performance was tested using simulated growth curves for a range of life-history types. Individual age at maturation, energy acquisition rate and the sum of maintenance and reproductive investment rates, and their multivariate distribution, were accurately estimated. For the estimation of maintenance and reproductive investment rates separately, biases were observed for life-histories with a large imbalance between these traits. For low reproductive investment rates and high maintenance rates, reproductive investment rate estimates were strongly biased whereas maintenance rate estimates were not, the reverse holding in the opposite situation. The method was applied to individual growth curves back-calculated from otoliths of North Sea plaice (Pleuronectes platessa) and from scales of Norwegian spring spawning herring (Clupea harengus). For plaice, maturity ogives derived from our individual estimates of age at maturation were almost identical to the maturity ogives based on gonad observation in catch samples. For herring, we observed 51.5% of agreement between our individual estimates and those directly obtained from scale reading, with a difference lower than 1 year in 97% of cases. We conclude that the method is a powerful tool to estimate the distribution of correlated life-history traits for any species for which individual growth curves are available.

Growing evidence suggests that fishing may induce rapid contemporary evolution in certain life-history traits. This study analyzes fisheries-induced changes in life-history traits describing growth, maturation, and reproduction, using an individual-based eco-genetic model that captures both the population dynamics and changes in genetic trait values. The model was successfully calibrated to match the observed life-history traits of female North Sea plaice Pleuronectes platessa around the years 1900 and 2000. On this basis, we report the following findings. First, the model indicates changes in 3 evolving life-history traits: the intercept of the maturation reaction norm decreases by 27%, the weight-specific reproductive-investment rate increases by 10%, and the weight-specific energy-acquisition rate increases by 1%. Together, these changes reduce the weight at maturation by 46% and the asymptotic body weight by 28% relative to the intensification of fishing around 1900. Second, while the maturation reaction norm and reproductive-investment rate change monotonically over time, the energy-acquisition rate follows a more complex course: after an initial increase during the first 50 yr, it remains constant for about 30 yr and then starts to decline. Third, our analysis indicates that North Sea plaice has not yet attained a new evolutionary equilibrium: it must be expected to evolve further towards earlier maturation, increased reproductive investment, and lower adult body size. Fourth, when fishing continues in our model 100 yr into the future, the pace of evolution slows down for the maturation reaction norm and the rate of en ergy acquisition, whereas no such slowing down is expected for the rate of reproductive investment.

Understanding of spatial patterns in life-history traits can help fisheries management focus on biologically and functionally relevant stock units. In the present study, we examined lifehistory variation in growth, condition and maturation of the Baltic herring Clupea harengus membras among different areas of the Baltic Sea. As expected based on environmental gradients, herring grew faster in southern than in northern areas. The condition factor for young individuals was higher in the north, but higher for older individuals in the south. Probabilistic maturation reaction norms (PMRNs) based on age, length and condition indicated counter-gradient variation: young herring in the northern areas reached the size at which they had a 50% probability of maturing when they were comparatively smaller than the southern specimens. However, the north-south differences in PMRNs were reversed in older age groups. This indicated that maturation of herring in the north was more size dependent (zero PMRN slope) than it was for herring in the south, where maturation was predominantly determined by age (negative PMRN slope). The geographical differentiation in maturation schedules would potentially translated into divergent changes in recruitment in response to changes in density-dependent growth and, hence, also fishing patterns.KEY WORDS: Clupeid · Counter-gradient variation · Life-history evolution · Phenotypic plasticity · PMRN · Size-selective fishing Resale or republication not permitted without written consent of the publisher