Transcript The Overlooked Evolutionary Dimension of Modern Fisheries Ulf Dieckmann Mikko Heino

The Overlooked Evolutionary
Dimension of Modern Fisheries
Ulf Dieckmann
Laxenburg, Austria
Mikko Heino
Bergen, Norway
Adriaan Rijnsdorp
IJmuiden, The Netherlands
David Conover
Stony Brook, USA
David Reznick
Riverside, USA
Richard Law
York, UK
The Overlooked Evolutionary Dimension
To be shown in this session:
 Modern fishing results in such substantial changes of
mortality patterns that evolutionary responses of
stocks are inevitable.
 Such changes are not as slow as is widely believed:
Significant evolution can occur within 10 or 20 years.
 Evolutionary changes are not necessarily beneficial,
neither to the stock nor to the exploiting agents.
 Once evolutionary changes have occurred, they may
be very difficult to reverse.
 In short: Fishing does not only change the numbers,
but also the traits of exploited fish.
Session Overview
Ulf Dieckmann: Overview, Northeast Atlantic
Mikko Heino: Northwest Atlantic
Adriaan Rijnsdorp: North Sea
David Conover: Lab Experiments
David Reznick: Field Experiments
Richard Law: Future Implications
Background
World Fisheries Have Reached a Ceiling
75% of Stocks Are Maximally Exploited
}
75%
Fisheries-induced Evolution
Initial composition
After fishing
After reproduction
Which Traits Are at Risk?

Age and size at maturation:
Reproducing late may not be a viable option.

Reproductive effort:
Saving for future reproduction may be futile.

Growth rate:
Staying below mesh size pays.

Behavior:
Reducing exposure to fishing is selected.
Focus of
my talk
The Case of
Northeast
Arctic Cod
Northeast Arctic Cod: Stock Structure
With ca. 2 million tons
per year, Northeast
Arctic cod is one of the
most important gadoid
stocks worldwide.
Feeding grounds
(mature & juvenile fish)
Spawning grounds
(only mature fish)
Northeast Arctic cod
Northeast Arctic Cod: Fishing History
1
0.9
Northeast Arctic cod
Immature
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1996
1992
1988
1984
1980
1976
1972
1968
1964
1960
1956
1952
1948
1944
1940
1936
1932
Mature
Northeast Arctic Cod: Stock Response
Continual decline in key
life-history characters
Length at maturation
Age at maturation
Northeast Arctic cod
Year
Two Hypotheses

Compensatory Response (Plastic Effect):
Decreased biomass > Increased growth > Earlier maturation
and/or

Reaction Norm Evolution (Genetic Effect):
Shift in maturation reaction norm > Earlier maturation at smaller size
Maturation Reaction Norms: Definition
Size
75% maturing
50% maturing
Maturation
25% maturing
Age
Neither the growth
trajectories nor the
reaction norm need
to be straight.
Maturation Reaction Norms: Utility
Faster growth (compensatory response)
Length
Baseline
Age
Earlier maturation
Faster growth & earlier maturation
Northeast Arctic Cod: Evolutionary Change
Northeast Arctic cod
100
Length (cm)
1923
1990
Significant shift in maturation reaction norm
50
5
Age (years)
12
Understanding
the Past,
Predicting
the Future
Two Salient Questions
Given the mounting empirical evidence for
fisheries-induced adaptive change, are the
observed rates of selection compatible with the
predictions of genetic models?
How can we anticipate the future course of
fisheries-induced adaptive change and
evaluate the impact of potential management
measures?
Model Structure

Five characteristics of individuals are tracked through time:
Age
Maturation
status
Reaction norm
position
Reaction norm
angle
Size
Stock
Dynamics
Demography
Evolution
Modeling Northeast Arctic Cod

0.8
0.7
Immature
0.6
0.5
0.4
0.3
0.2
 Estimated size selectivity of fishing
gear taken into account
1996
1992
1988
1984
1980
1976
1972
1968
1960
1964
Mature
0.1
0
1956

1
0.9
1952

Fimmature = 0.05 and Fmature = 0.2
 Contemporary regime:
Fimmature = 0.4 and Fmature = 0.3
1948


 Historical regime:
1944

correlated with stock biomass
Growth increments of mature
individuals depend on size and
gonadosomatic index
Natural mortality of 0.2
Density-dependent newborn
mortality
Density-dependent cannibalism
on age classes 1 and 2
Linear maturation reaction norm
of constant width
Fecundity allometrically depends
on size
Fishing Mortality
1940
 Linear growth before maturation
 Growth increments negatively

1936
Demography
1932

Modeling Evolutionary Speed 1
12
10
8
Today
Age at maturation (years)
Heritability = 0.2
6
4
2
0
ca. 40 years
Historical
regime
Current
regime
0
Time (years)
100
Modeling Evolutionary Speed 2
12
10
8
6
Today
Age at maturation (years)
Heritability = 0.2
4
2
0
ca. 250 years
Current
regime
Historical
regime
0
Time (years)
100
Conclusions

Fisheries-induced evolution has been with us for several
decades without having been recognized.

The speed of such evolution is much faster than
previously believed .

Fisheries-induced evolution often reduces yield.

Models suggest that each year during which current
exploitation continues requires several years of
evolutionary recovery:
A “Darwinian debt” to be paid by future generations.