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Bruno Ernande
Channel-North Sea Fisheries Unit
Taking a systems approach, April 2011
Harvest-induced life-history
evolution 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
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
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
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
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
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
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 changes are 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)
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
Outline
1. Empirical evidence: the nature of adaptive processes
2. Evolutionary equilibria expected under fishing-induced selection
and demographic implications
Deterministic cohort-based model of phenotypic evolution
3. Harvest-induced evolutionary rates and potential mitigation
measures
Deterministic cohort-based model of quantitative genetic evolution (coupled
with dynamic optimization)
4. Fisheries-induced adaptive vs. neutral evolution and effects on
genetic diversity
Stochastic individual-based model of genetic evolution
Bruno Ernande
Channel-North Sea Fisheries Unit
Taking a systems approach, April 2011
1. Empirical evidence:
The nature of adaptive processes
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
Northern cod case study: background information
A50 (année)
7
A50 : age at which 50% of the fish are
mature
Continuous decline
since the 70’s
6
5
4
1980
1990
2000
Année
Olsen et al. (2004) Nature
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
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
Taking a systems approach, April 2011
Baseline
Compensatory response (fast growth)
size
Bruno Ernande
Channel-North Sea Fisheries Unit
Maturation reaction norm (MRN) analysis: Principle
Evolution
Age
Compensatory response and evolution
Heino et al. (2002a, 2002b) Evolution & ICES J. Mar. Sci.
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
Northern cod case study: fisheries-induced evolution
60
Length (cm)
1980
Whithin 7 years, age
and length at which the
probability of
maturating is 50%
decreased by about one
year and 7 cm
1980
50
1987
40
1987
30
4
6
5
7
Age (years)
Olsen et al. (2004) Nature
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
A widespread phenomenon
Magnitude and rate* of
evolutionary change
Species
Population or stock
Data period
American plaice Hippoglossoides
platessoides
Labrador, Newfoundland
1973–1999
22–47%
12–31
(S23)
Grand Bank
1969–2000
19–49%
10–32
(S23)
St. Pierre Bank
1972–1999
14–42%
7.1–26
(S23)
Northeast Arctic
1932–1998
12%
2.1
(S11)
Georges Bank
1970–1998
26–41%
15–26
(S24)
Gulf of Maine
1970–1998
25–26%
14–15
(S24)
Northern†
(1977–)1981–2002
–
11–27%
7–19#
11–21
(S25)
(S26)
Southern Grand Bank†
1971–2002
18%
9.3–9.6
(S26)
St. Pierre Bank†
1972–2002
25–32%
15–20
(S26)
Baltic
1988–2003
21%
16
(S27)
Atlantic herring Clupea harengus
Norwegian springspawning
1935–2000
3%
0.7
(S28)
Plaice Pleuronectes platessa
North Sea
1957–2001
1957–2001
13%
14%
4.7
4.6
(S19)
(S29)
Sole Solea solea
Southern North Sea
1958–2000
11%
4.1
(S30)
Atlantic cod Gadus morhua
Reference
Jorgensen et al. (2007) Science
Bruno Ernande
Channel-North Sea Fisheries Unit
Taking a systems approach, April 2011
2. Evolutionary equilibria expected under fishinginduced selection and demographic implications
Deterministic cohort-based model of phenotypic evolution
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
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)
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
Life history dynamics
∎ Maturation process: maturation occurs when the growth trajectory intersects with the
maturation reaction norm
Trade-off between
reproduction and
somatic growth rate
maturation reaction norm
Δ
adults
juveniles
larvae
Environmental variability
metamorphosis
in growth migration
trajectoriesto a new
environment
Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B
Taking a systems approach, April 2011
∎ 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
1
Fishing Mortality
Bruno Ernande
Channel-North Sea Fisheries Unit
Harvesting and management rules
Quotas
positive
density-dependence
density-independence
negative
density-dependence
0
Stock
Size
Stock Biomass
Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B
Taking a systems approach, April 2011
Evolution under size-dependent harvesting
Bruno Ernande
Channel-North Sea Fisheries Unit
Quota
Constant Rate
Constant Stock Size
Unfished sizes
Unfished sizes
Unfished sizes
Unfished sizes
Unfished sizes
Unfished sizes
Unfished sizes
Unfished sizes
Unfished sizes
size (a)
H0
age (a)
Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B
Taking a systems approach, April 2011
∎ 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
Evolutionary time
Fishing mortality
Proportion of
original value
Bruno Ernande
Channel-North Sea Fisheries Unit
Consequences for demography
population biomass
mortality
Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B
Bruno Ernande
Channel-North Sea Fisheries Unit
Taking a systems approach, April 2011
3. Harvest-induced evolutionary rates
and potential mitigation measures
Deterministic cohort-based model of quantitative genetic
evolution (coupled with dynamic optimization)
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
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)
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
Northeast Arctic cod: Energy allocation model
States
Age
Body length
Stored energy
External factors
Fishing
mortality
Growth
Food
intake
Stored energy
Offspring
Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.
Taking a systems approach, April 2011
Abundance
Bruno Ernande
Channel-North Sea Fisheries Unit
The effect of gear selectivity: Contribution to reproduction
Reproduction
Reproduction
Size (length)
Fish
reproducing
here…
Size (length)
…do not here
Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
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.
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
The effect of gear selectivity: Gillnets 186 mm mesh size
Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.
Taking a systems approach, April 2011
Jørgensen (1990)
Russian data (ICES)
Norwegian data (ICES)
No fishing during World War II –
density dependence
Mean age at maturation
1.0
Gear selectivity
Bruno Ernande
Channel-North Sea Fisheries Unit
Evolutionary effects of gear selectivity
0.8
0.6
0.4
0.2
0.0
25
50
75
100
Length (cm)
Current
125
150
12
10
8
6
4
1900
2000
Year
2100
Gillnet 186 mm
Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.
Bruno Ernande
Channel-North Sea Fisheries Unit
Taking a systems approach, April 2011
4. Fisheries-induced adaptive vs. neutral evolution
and effects on genetic diversity
Stochastic individual-based model of genetic evolution
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
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
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
Model structure
Life history:
Bioenergetics:
-Potential growth
-Maturation RN
intercept & slope
-Adult growth
investment: initial
& decay
Mating:
-Panmixia
-Random encounter
-Multiple mating
Density-dependent
recruitment
Density-dependent
energy acquisition
-Growth
-Maturation
-Reproduction
-Mortality
Inheritance:
Multi-loci
additive/neutral
genetics
Marty, Dieckmann & Ernande. In prep
Taking a systems approach, April 2011
Multi-trait fisheries-induced evolution
Growth initial investment
Adult growth investment
Growth investment decay
Bruno Ernande
Channel-North Sea Fisheries Unit
Growth potential
Smaller size-at-age
Stronger fecundity-at-age
MRN intercept
MRN slope
Younger age at maturation
Smaller size at maturation
Marty, Dieckmann & Ernande. In prep
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
Erosion of genetic variance of evolving traits
Growth potential
Growth intial investment
MRN intercept
Growth investment decay
MRN slope
Marty, Dieckmann & Ernande. In prep
Taking a systems approach, April 2011
Contribution of neutral vs. adaptive evolution to genetic erosion
Growth intial investment
Growth investment decay
Bruno Ernande
Channel-North Sea Fisheries Unit
Growth potential
MRN intercept
MRN slope
Marty, Dieckmann & Ernande. In prep
Taking a systems approach, April 2011
Bruno Ernande
Channel-North Sea Fisheries Unit
Conclusions
∎ Observed trends in exploited fish life history traits are compatible with expected fisheriesinduced 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.