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The Overlooked Evolutionary Dimension of Modern Fisheries

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Presentation on theme: "The Overlooked Evolutionary Dimension of Modern Fisheries"— Presentation transcript:

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

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