Harvest-induced life-history evolution in exploited fish populations

1. Taking a systems approach, April 2011 Harvest-induced life-historyevolution in exploited fish populations Empirical evidence and forecasting of evolutionary changes and their demographic consequences Bruno Ernande Laboratoire Ressources Halieutiques IFREMER Boulogne-sur-Mer, France

2. Taking a systems approach, April 2011 Fishing as a global issue • More than 80% of fish stocks are fully or overexploited • World captures have reached a ceiling since the late 80’s FAO.2010.SOIA report

3. Taking a systems approach, April 2011 Fisheries-induced selection and expected adaptive changes • Fisheries-induced selection: fishing mortality is 4 to 5 times higher than natural mortality • Life history traits are primarily under selection • Age and size at maturation:Fish that reproduce too late are fished before they can do so. • Reproductive effort:Investing into future reproduction is not useful when there is none. • Growth rate:Small fish that stay below mesh size for longer may have more offspring during their lifetime. • Adaptive changes in life history traits may imply both • Fisheries-induced phenotypically plasticity • Fisheries-induced adaptive evolution (adaptive genetic change) • Nonadaptive changes in life history traits may arise from • Fisheries-induced neutral evolution

4. Taking a systems approach, April 2011 Issues at stake • Changes in life history traits affect stocks’ demography • Fisheries production • Population viability • Sustainable exploitation and restoration of the stocks (Johannesburg 2002) • The nature of processes is of primary importance for management purposes • Plastics changesare reversed on a within-generation timescale • Evolutionary changes on a between-generation timescale(decades).  Fisheries Common Policy (EU) • Biodiversity • Changes in life history traits  functional diversity • Changes in genetic composition  genetic diversity  Reduction of the alteration of biodiversity (Green Paper EU 2001; Johannesburg 2002)

5. Taking a systems approach, April 2011 Outline • Empirical evidence: the nature of adaptive processes • Evolutionary equilibria expected under fishing-induced selection and demographic implications Deterministic cohort-based model of phenotypic evolution • Harvest-induced evolutionary rates and potential mitigation measuresDeterministic cohort-based model of quantitative genetic evolution (coupled with dynamic optimization) • Fisheries-induced adaptive vs. neutral evolution and effects on genetic diversityStochastic individual-based model of genetic evolution

6. Taking a systems approach, April 2011 1.Empirical evidence: The nature of adaptive processes

7. Continuous decline since the 70’s A50 (année) Année Taking a systems approach, April 2011 Northern cod case study: background information A50 : age at which 50% of the fish are mature Olsen et al. (2004) Nature

8. Taking a systems approach, April 2011 Two hypotheses • Compensatory response (phenotypic plasticity):Decreased biomass > Increased growth > Earlier maturation and/or • Evolution of age and size at maturation (genetic modification):Size-selective fishing favors genotypes characterized by early maturation at small size Olsen et al. (2004) Nature

9. Compensatory response (fast growth) Evolution Compensatory response and evolution Taking a systems approach, April 2011 Maturation reaction norm (MRN) analysis: Principle Baseline size Reaction norm Growth trajectories Age Heino et al. (2002a, 2002b) Evolution & ICES J. Mar. Sci.

10. Taking a systems approach, April 2011 Northern cod case study: fisheries-induced evolution 1980 Whithin 7 years, age and length at which the probability of maturating is 50% decreased by about one year and 7 cm Length (cm) 1987 Age (years) Olsen et al. (2004) Nature

11. Taking a systems approach, April 2011 A widespread phenomenon Jorgensen et al. (2007) Science

12. Taking a systems approach, April 2011 2. Evolutionary equilibria expected under fishing-induced selection and demographic implications Deterministic cohort-based model of phenotypic evolution

13. Taking a systems approach, April 2011 Questions and modelling approach • Is harvesting a sufficient condition to generate observed trends in life history traits? • Expected life history traits’ evolutionary equilibria under fishing-induced selection • What are the expected qualitative demographic implications of life history trait changes? • Stock demographic characteristics at fisheries-induced evolutionary equilibria • Modelling approach: deterministic cohort-based model of phenotypic evolution • Life history traits: phenomenological description of growth, maturation reaction norm & size-dependent fecundity • Population dynamics: deterministic age and size structured population model  Physiologically structured population model (deRoos, Metz and Diekmann 1992 ) • Evolutionary dynamics: deterministic model of phenotypic evolution Adaptive Dynamics (Metz et al. 1996; Dieckmann and Law 1996)

14. Trade-off between reproduction and somatic growth rate Environmental variability in growth trajectories Taking a systems approach, April 2011 Life history dynamics • Maturation process: maturation occurs when the growth trajectory intersects with the maturation reaction norm maturation reaction norm Δ adults growth trajectory juveniles migration to a new environment metamorphosis larvae Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B

15. Taking a systems approach, April 2011 Harvesting and management rules • Mortality rates increase because of harvesting. Three management rules: • Fixed Quotas: positive density-dependence • Constant Harvesting Rate: density-independence • Constant Stock Size or Constant Escapement: negative density-dependence Quotas positive density-dependence Fishing Mortality density-independence negative density-dependence Stock Size Stock Biomass Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B

16. Unfished sizes Unfished sizes Unfished sizes Unfished sizes Unfished sizes Unfished sizes Taking a systems approach, April 2011 Evolution under size-dependent harvesting Quota Constant Rate Constant Stock Size H0 size (a) Unfished sizes Unfished sizes Unfished sizes age (a) Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B

17. Taking a systems approach, April 2011 Consequences for demography • Evolutionary induced decrease in population biomass due to a decrease in adult mean size and population density. Quota Constant Rate Constant Stock Size mean adult size population density Proportion of original value Fishing mortality Evolutionary time population biomass mortality Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B

18. Taking a systems approach, April 2011 3. Harvest-induced evolutionary ratesand potential mitigation measuresDeterministic cohort-based model of quantitative genetic evolution (coupled with dynamic optimization)

19. Taking a systems approach, April 2011 Questions and modelling approach • Can we predict rates of fisheries-induced evolutionary changes? • Evolutionary rates depend on selection gradient and trait’s genetic variation: underlying genetics need to be accounted for • What are the potential mitigation measures at hand? • There is strong socio-economic pressure to maintain fishing intensity, but gear type might be easier to manage • Modelling approach: Deterministic cohort-based model of quantitative genetic evolution • Life history traits: state-dependent energy allocation model describing growth, maturation and fecundity • Population dynamics: deterministic model of population structured according to age, size and energy reserve  Matrix population model (Caswell 2001) • Evolutionary dynamics: deterministic model of genetic evolution  Quantitative genetics model (Lande 1982)

20. States External factors Age Body length Stored energy Fishing mortality Food intake Growth Offspring Taking a systems approach, April 2011 Northeast Arctic cod: Energy allocation model Stored energy Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.

21. Abundance Size (length) Size (length) Taking a systems approach, April 2011 The effect of gear selectivity: Contribution to reproduction Reproduction Reproduction Fishreproducing here… …do not here Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.

22. Taking a systems approach, April 2011 The effect of gear selectivity: Current practice (trawls mostly) Early-maturing life history strategies have high fitness Initial distribution Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.

23. Taking a systems approach, April 2011 The effect of gear selectivity: Gillnets 186 mm mesh size Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.

24. Jørgensen (1990) Russian data (ICES) Norwegian data (ICES) Taking a systems approach, April 2011 Evolutionary effects of gear selectivity No fishing during World War II – density dependence 1.0 12 0.8 10 0.6 Mean age at maturation Gear selectivity 8 0.4 6 0.2 4 0.0 1900 2000 2100 25 50 75 100 125 150 Year Length (cm) Gillnet 186 mm Current Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.

25. Taking a systems approach, April 2011 4. Fisheries-induced adaptive vs. neutral evolution and effects on genetic diversityStochastic individual-based model of genetic evolution

26. Taking a systems approach, April 2011 Questions and modelling approach • Are there synergetic or compensatory effects between evolutionary changes in different life history traits? • Multi-trait fisheries-induced evolution • What is the relative importance of fisheries-induced adaptive and neutral evolution in life history trait changes? • Does fishing-induced (adaptive and neutral) evolution erode genetic variability? • Underlying stochastic genetics need to be accounted for • Modelling approach: Stochastic individual-based model of genetic evolution • Life history traits: Energy allocation model describing growth and fecundity (Quince et al.2008) + maturation reaction norm • Population dynamics: emergent from stochastic events of birth and death  Individual-based model • Evolutionary dynamics: emergent from an explicit multi-locus additive genetic model for life history traits + multi-locus neutral genetic model  Individual-based model

27. Life history: -Growth -Maturation -Reproduction -Mortality Population and Evolutionary Dynamics Bioenergetics:-Potential growth -Maturation RN intercept & slope-Adult growth investment: initial& decay Mating: -Panmixia -Random encounter -Multiple mating Density-dependentenergy acquisition Density-dependentrecruitment Inheritance:Multi-lociadditive/neutralgenetics Taking a systems approach, April 2011 Model structure Marty, Dieckmann & Ernande. In prep

28. Taking a systems approach, April 2011 Multi-trait fisheries-induced evolution Growth potential Adult growth investment Smaller size-at-age Stronger fecundity-at-age Growth initial investment Growth investment decay MRN intercept MRN slope Younger age at maturation Smaller size at maturation Marty, Dieckmann & Ernande. In prep

29. Taking a systems approach, April 2011 Erosion of genetic variance of evolving traits Growth investment decay Growth potential Growth intial investment MRN slope MRN intercept Marty, Dieckmann & Ernande. In prep

30. Taking a systems approach, April 2011 Contribution of neutral vs. adaptive evolution to genetic erosion Growth potential Growth intial investment Growth investment decay MRN intercept MRN slope Marty, Dieckmann & Ernande. In prep

31. Taking a systems approach, April 2011 Conclusions • Observed trends in exploited fish life history traits are compatible with expected fisheries-induced equilibria • Evolutionary rates are rapid: a few decades are enough for substantial changes • Maturation seem to be the most sensitive trait • Fishing-induced adaptive and neutral evolution may induce irreversible erosion of genetic diversity • The consequences of these evolutionary changes on stock abundance and sustainability may be strong and would be overlooked by pure population dynamics models: necessity to take evolutionary trends into account in management practices. • The prevalent system of management currently, quotas, seems to be the worse management practice in terms of fisheries-induced evolution • Policies on gear selectivity may be a way to mitigate fisheries-induced evolutionary changes: alleviating the selectivity on large individuals may reverse the selective pressure.