The OverlookedEvolutionary Dimension of

Modern Fisheries

Ulf Dieckmann1 and Mikko Heino2,1

1 International Institute for Applied Systems Analysis, Austria2 University of Bergen, Norway

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

World excluding China

China

Total catch in millions of tonnes

UN Food and Agriculture Organization

80

20

40

60

0

100

1950 1960 1970 1980 1990 2000

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

World Fisheries Have Reached a Ceiling

Shifting Baselines

Across generations, we lose track of what was natural

Example: Distribution of large fish in the North Atlantic

Tonnes per square km

19001900 20002000Christensen et al. Christensen et al. (2003)(2003)

Two Key Dimensions of Fishing

EcologyEcology

Changes innumbers of fish

EvolutionEvolution

Changes inheritable features of fish

Part 1: Ecological Effects of FishingEcological Effects of Fishing

EvolutionEcologyEcology

Changes innumbers of fish

Changes inheritable features of fish

Fishing Down the Food Web

Pauly et al. (1998) © Pauly et al. (1998) © Nature Publishing GroupNature Publishing Group

Once large fish are gone, small fish further down the food web are caught

Discarding

Fish are killed without being landed

© © Elliott NorseElliott Norse

“Shrimp catch”

© © Simon JenningsSimon Jennings

“Cod catch”

• Non-valuable species

• Low-quality target fish

• Over-quota species

• Under-sized target fish

Collateral Damage

Bottom trawls destroy ocean-floor ecosystems

© © Peter AusterPeter Auster

Provisioning

Productshumansderive

Ecosystem Services

Supporting

Fundamentallong-termprocesses

Four categories defined by Millennium Ecosystem Assessment

Regulating

Benefits fromecosystemregulation

Cultural

Education,recreation &enrichment

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)

Part 2: Evolutionary Effects of FishingEvolutionary Effects of Fishing

Ecology EvolutionEvolution

Changes innumbers of fish

Changes in heritable features of fish

Fisheries-induced Evolution

Initial compositionInitial composition After fishingAfter fishing After reproductionAfter reproduction

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

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

Focushere

© © Google EarthGoogle Earth

Feeding groundsBarents Sea,mature & juvenile fish

Spawning groundsNorwegian coast,only mature fish

With a catch of 400,000 tonnes per year, Northeast Arctic cod is one of the most important European stocks

Northeast Arctic Cod: Stock Structure

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

Northeast Arctic Cod: Evolutionary ChangeL

eng

th a

t mat

ura

tion

at a

ge

7 (

cm)

1930 1970 2005

70

100

90

80

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%

Until 1970Until 1970

TodayToday

Total catchin thousands of tonnes800

0

200

400

600

1960 1992

© © Google EarthGoogle Earth

Northern Cod: Fishing History

The northern cod stock collapsed in 1992,in one of the worst disasters of modern fishing

Non-Non-CanadianCanadian

CanadianCanadian

Moratorium

1975 1992 2004

30

80

70

60

50

40

Len

gth

at m

atu

ratio

na

t ag

e 5

(cm

)

Northern Cod: Evolutionary Change

Early warning

A strong negative trend in maturation schedule, as predicted by theory

1978 19920%

80%

100%

Sta

tistic

al c

onf

ide

nce

in n

ega

tive

tre

nd

1985

7 yearsbefore collapse

Northern Cod: Early Warning

A negative trend in the maturation schedule could have been detected with a confidence of more than 80% already 7 years before the collapse

Additional Case Studies

Atlantic codGeorges BankGulf of Maine

Southern Grand BankSt. Pierre Bank

American plaiceLabrador

Grand BankSt. Pierre Bank

Small yellow croaker Yellow Sea

Sole North Sea

Plaice North Sea

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

0 100Time (years)

CurrentCurrentfishingfishing

Ag

e a

t mat

ura

tion

(yea

rs)

12

10

8

6

4

2

0

HistoricalHistoricalfishingfishing

Model of Northeast Arctic cod

Fast Pace of Evolutionary Decline

ca. 40 yearsca. 40 yearsT

oda

yT

oda

y

Ag

e a

t mat

ura

tion

(yea

rs)

HistoricalHistoricalfishingfishing

0 100Time (years)

12

10

8

6

4

2

0

CurrentCurrentfishingfishing

Model of Northeast Arctic cod

Slow Pace of Evolutionary Recovery

To

day

To

day

ca. 250 yearsca. 250 years

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