Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Harvest-induced life-historyevolution in exploited fish populations
Bruno Ernande
Laboratoire Ressources Halieutiques
IFREMER
Boulogne-sur-Mer, France
Empirical evidence and forecasting of evolutionary changes and their demographic consequences
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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 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)
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
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 measuresDeterministic cohort-based model of quantitative genetic evolution (coupled with dynamic optimization)
4. Fisheries-induced adaptive vs. neutral evolution and effects on genetic diversityStochastic individual-based model of genetic evolution
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
1. Empirical evidence: The nature of adaptive processes
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Northern cod case study: background information
Olsen et al. (2004) Nature
1980 200019904
5
6
7 Continuous decline since the 70’s
Année
A50
(ann
ée)
A50 : age at which 50% of the fish are mature
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
∎ 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
Two hypotheses
Olsen et al. (2004) Nature
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Baseline Compensatory response (fast growth)
Age
size
Growth trajectories
Reaction norm
Maturation reaction norm (MRN) analysis: Principle
Evolution Compensatory response and evolution
Heino et al. (2002a, 2002b) Evolution & ICES J. Mar. Sci.
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
1980
Northern cod case study: fisheries-induced evolution
Age (years)
Leng
th (
cm)
4 5 6 730
60
50
40
1980
1987
Whithin 7 years, age and length at which the
probability of maturating is 50%
decreased by about one year and 7 cm1987
Olsen et al. (2004) Nature
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
A widespread phenomenon
Species Population or stock Data period Magnitude and rate* of evolutionary change Reference
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)
Atlantic cod Gadus morhua 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 spring-spawning
1935–2000 3% 0.7 (S28)
Plaice Pleuronectes platessa North Sea 1957–20011957–2001
13%14%
4.74.6
(S19)(S29)
Sole Solea solea Southern North Sea 1958–2000 11% 4.1 (S30)
Jorgensen et al. (2007) Science
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
2. Evolutionary equilibria expected under fishing-induced selection and demographic implications
Deterministic cohort-based model of phenotypic evolution
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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)
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Δ
migration to a new environment
growth trajectory
Trade-off between reproduction and
somatic growth rate
metamorphosisEnvironmental variability
in growth trajectories
maturation reaction norm
juveniles
larvae
adults
Life history dynamics
∎ Maturation process: maturation occurs when the growth trajectory intersects with the maturation reaction norm
Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
0
1
Stock Biomass
Fish
ing
Mor
talit
y
positivedensity-dependence
negativedensity-dependence
density-independence
Quotas
Stock Size
Harvesting and management rules
∎ Mortality rates increase because of harvesting. Three management rules:Fixed Quotas: positive density-dependence Constant Harvesting Rate: density-independenceConstant Stock Size or Constant Escapement: negative density-dependence
Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Evolution under size-dependent harvesting
Quota Constant Rate Constant Stock Size
age (a)
size
(a)
Unfished sizesUnfished sizes
Unfished sizes Unfished sizes Unfished sizes
Unfished sizes Unfished sizes Unfished sizes
Unfished sizes
H0
Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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 biomass
population density
mortality
Evolutionary time
Pro
port
ion
of
orig
inal
val
ue
Fishing m
ortality
Ernande, Dieckmann & Heino. 2004. Proc Roy Soc B
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
3. Harvest-induced evolutionary ratesand potential mitigation measures
Deterministic cohort-based model of quantitative genetic evolution (coupled with dynamic optimization)
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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)
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Food intake
Stored energy
OffspringOffspring
Growth
External factors
Fishing mortality
States
Age Body length Stored energy
Northeast Arctic cod: Energy allocation model
Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
The effect of gear selectivity: Contribution to reproduction
Size (length)
ReproductionReproduction
…do not here
Size (length)
Ab
un
dan
ce
Fishreproducing
here…
Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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.
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
The effect of gear selectivity: Gillnets 186 mm mesh size
Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Evolutionary effects of gear selectivity
Current Gillnet 186 mm
Jørgensen (1990)Russian data (ICES)Norwegian data (ICES)
No fishing during World War II – density dependence
Jorgensen, Ernande & Fiksen. 2009. Evol. Appl.
4
6
8
10
12
1900 2000 2100Year
Mean
ag
e a
t m
atu
rati
on
0.0
0.2
0.4
0.6
0.8
1.0
25 50 75 100 125 150Length (cm)
Gear
sele
cti
vit
y
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
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
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Model structure
Inheritance:Multi-lociadditive/neutralgenetics
Life history:-Growth-Maturation-Reproduction-Mortality
Bioenergetics:-Potential growth-Maturation RN intercept & slope-Adult growth investment: initial& decay
Mating:-Panmixia-Random encounter-Multiple mating
Density-dependent
recruitment
Den
sity
-dep
ende
nten
ergy
acq
uisi
tion
Marty, Dieckmann & Ernande. In prep
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Multi-trait fisheries-induced evolutionGrowth potential Adult growth investment
Gro
wth
initi
al in
vest
men
t Grow
th investment decay
MRN intercept MRN slope
Marty, Dieckmann & Ernande. In prep
Smaller size-at-ageStronger fecundity-at-age
Younger age at maturationSmaller size at maturation
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Erosion of genetic variance of evolving traits
Growth potential Growth intial investment Growth investment decay
MRN intercept MRN slope
Marty, Dieckmann & Ernande. In prep
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
Contribution of neutral vs. adaptive evolution to genetic erosionGrowth potential Growth intial investment Growth investment decay
MRN intercept MRN slope
Marty, Dieckmann & Ernande. In prep
Bru
no E
rnan
deC
hann
el-N
orth
Sea
Fis
herie
s U
nit
Taking a systems approach, April 2011
∎ 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.
Conclusions
