1. The Overlooked Evolutionary Dimension of Modern Fisheries
Ulf Dieckmann1 and Mikko Heino2,1
1 International Institute for Applied Systems Analysis, Austria 2 University of Bergen, Norway

2. Fishing the World’s Oceans
A large fraction of our living natural resources are extracted from the oceans
Annual production
 100 million tonnes
 17 kg per capita, on average
 16% of world animal-protein supply
 US$ 85 billion
Yet, world fisheries are in a global crisis

3. World Fisheries Have Reached a Ceiling
World excluding China
China
Total catch in millions of tonnes
UN Food and Agriculture Organization 80 20 40 60
100
1950
1960
1970
1980
1990
2000

4. World Fisheries Have Reached a Ceiling
Percentage of stocks assessed
80%
20%
40%
60% 0%
Maximally exploited
Overexploited
UN Food and Agriculture Organization
1980
1990
2000

5. Shifting Baselines
Across generations, we lose track of what was natural
Example: Distribution of large fish in the North Atlantic
Tonnes per square km
1900
2000
Christensen et al. (2003)

6. Two Key Dimensions of Fishing
Ecology
Changes in numbers of fish
Evolution
Changes in heritable features of fish

7. Part 1: Ecological Effects of Fishing
Ecology
Evolution
Changes in numbers of fish
Changes in heritable features of fish

8. Fishing Down the Food Web
Once large fish are gone, small fish further down the food web are caught
Pauly et al. (1998) © Nature Publishing Group

9. Discarding Fish are killed without being landed “Shrimp catch”
© Elliott Norse
“Shrimp catch”
© Simon Jennings
“Cod catch”
Non-valuable species
Low-quality target fish
Over-quota species
Under-sized target fish

10. Collateral Damage Bottom trawls destroy ocean-floor ecosystems
© Peter Auster

11. Ecosystem Services Products humans derive
Four categories defined by Millennium Ecosystem Assessment
Provisioning
Products humans derive
Supporting
Fundamental long-term processes
Regulating
Benefits from ecosystem regulation
Cultural
Education, recreation & enrichment

12. Future Requirements Reduced exploitation
Less discards and collateral damage
Ecosystem-based fisheries management
Precautionary approach to risks
Marine protected areas
Restoration to maximum sustainable yield (mandated by 2015 by the 2002 UN World Summit on Sustainable Development)

13. Part 2: Evolutionary Effects of Fishing
Ecology
Evolution
Changes in numbers of fish
Changes in heritable features of fish

14. Fisheries-induced Evolution
Initial composition
After fishing
After reproduction

15. The Overlooked Evolutionary Dimension
Evolutionary responses of stocks are inevitable
Significant evolution can occur within just 10 to 20 years
Evolutionary changes are not necessarily beneficial
Such changes will be difficult to reverse

16. Which Traits Are at Risk?
Age and size at maturation  Reproducing late is impossible
Reproductive effort  Saving for future seasons is futile
Growth rate  Staying below mesh size prolongs life
Morphology and behavior  Avoiding fishing gear is advantageous
Focus here

17. Northeast Arctic Cod: Stock Structure
© Google Earth
Feeding grounds Barents Sea,
mature & juvenile fish
Spawning grounds Norwegian coast,
only mature fish
With a catch of 400,000 tonnes per year, Northeast Arctic cod is one of the most important European stocks

18. Northeast Arctic Cod: Fishing History
Fishing along the Norwegian coast has been intensive for centuries
Trawling in the Barents Sea started in the 1920s and reached its current high level around 1960
Evolution of earlier maturation at smaller size is thus expected

19. Northeast Arctic Cod: Evolutionary Change
Length at maturation
at age 7 (cm)
1930
1970
2005 70
100 90 80
Until 1970
Today
This shift in maturation schedule contributes to a drop in maturation age from 9-10 years to 5-6 years and reduces initial egg production by 50%

20. Northern Cod: Fishing History
© Google Earth
Total catch
in thousands of tonnes
800
200
400
600
1960
1992
Non-
Canadian
The northern cod stock collapsed in 1992, in one of the worst disasters of modern fishing

21. Northern Cod: Evolutionary Change
Moratorium
1975
1992
2004 30 80 70 60 50 40
Length at maturation
at age 5 (cm)
Early warning
A strong negative trend in maturation schedule, as predicted by theory

22. Northern Cod: Early Warning
1978
1992 0%
80%
100%
Statistical confidence
in negative trend
1985
7 years
before collapse
A negative trend in the maturation schedule could have been detected with a confidence of more than 80% already 7 years before the collapse

23. Additional Case Studies
Atlantic cod
Georges Bank
Gulf of Maine
Southern Grand Bank
St. Pierre Bank
Plaice
North Sea
Sole
North Sea
American plaice
Labrador
Grand Bank
St. Pierre Bank
Small yellow croaker
Yellow Sea

24. Modeling Fisheries-induced Evolution
To understand past fisheries-induced evolution
To forecast the direction, speed, and outcome of future fisheries-induced evolution
To predict the evolutionary vulnerability of species and stocks
To investigate the consequences of alternative management scenarios

25. Fast Pace of Evolutionary Decline
100
Time (years)
Current
fishing
Age at maturation (years) 12 10 8 6 4 2
Historical
Model of Northeast Arctic cod
ca. 40 years
Today

26. Slow Pace of Evolutionary Recovery
Age at maturation (years)
Historical
fishing
100
Time (years) 12 10 8 6 4 2
Current
Model of Northeast Arctic cod
Today
ca. 250 years

27. Conclusions
Fisheries-induced evolution has been with us for several decades without having been properly recognized
The speed of such evolution is much faster than previously believed
Fisheries-induced evolution affects demography and thus yield, stock stability, and recovery potential
Models suggest that each year during which current exploitation continues may require several years of evolutionary recovery:
A “Darwinian debt” to be paid by future generations