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The Overlooked Evolutionary Dimension of Modern Fisheries Ulf Dieckmann 1 and Mikko Heino 2,1 1 International Institute for Applied Systems Analysis, Austria.

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Presentation on theme: "The Overlooked Evolutionary Dimension of Modern Fisheries Ulf Dieckmann 1 and Mikko Heino 2,1 1 International Institute for Applied Systems Analysis, Austria."— Presentation transcript:

1 The Overlooked Evolutionary Dimension of Modern Fisheries Ulf Dieckmann 1 and Mikko Heino 2,1 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 excluding China China Total catch in millions of tonnes UN Food and Agriculture Organization World Fisheries Have Reached a Ceiling

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

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 Christensen et al. (2003)

6 Two Key Dimensions of FishingEcology Changes in numbers of fishEvolution Changes in heritable features of fish

7 Ecological Effects of Fishing Part 1: Ecological Effects of Fishing EvolutionEcology Changes in numbers of fish Changes in heritable features of fish

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

9 Discarding Fish are killed without being landed © 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 Provisioning Products humans derive Ecosystem Services Supporting Fundamental long-term processes Four categories defined by Millennium Ecosystem Assessment 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 Evolutionary Effects of Fishing Part 2: Evolutionary Effects of Fishing EcologyEvolution 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 © 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 Northeast Arctic Cod: Stock Structure

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) 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 1970 Today

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

21 Moratorium Length at maturation at age 5 (cm) Northern Cod: Evolutionary Change Early warning A strong negative trend in maturation schedule, as predicted by theory

22 % 80% 100% Statistical confidence in negative trend years before 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

23 Additional Case Studies Atlantic cod Georges Bank Gulf of Maine Southern Grand Bank St. Pierre Bank American plaice Labrador Grand Bank St. Pierre Bank Small yellow croaker Yellow Sea Sole North Sea Plaice North 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 0100 Time (years) Currentfishing Age at maturation (years) Historicalfishing Model of Northeast Arctic cod Fast Pace of Evolutionary Decline ca. 40 years Today

26 Age at maturation (years) Historicalfishing 0100 Time (years) Currentfishing Model of Northeast Arctic cod Slow Pace of Evolutionary Recovery 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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