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understanding the role of carp in south africa s largest impoundment

Global Player: Common carp (Cyprinus carpio) . Often perceived as pest speciesSuccessful invadersAdverse ecological impacts- Increased turbidity- Biodiversity loss- Competition with endemic speciesAppreciated angling speciesImportant protein source in many countries . Talk outline.

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understanding the role of carp in south africa s largest impoundment

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    1. Understanding the Role of Carp in South Africa’s largest impoundment Henning Winker*, O.L.F. Weyl , A.J. Booth and B.R. Ellender

    3. Talk outline Study area Lake Gariep Life history Age and Growth incl. Age validation Maturity Spawning dynamics Post-impoundment trends Gill net fleet standardisation Food web study Based C and N stable isotopes

    4. 1. Study Area

    5. 2. Life history

    6. Age and Growth: Age Validation Preliminary Result: Two Rings per year!!!!

    7. Growth RateMean Length / Weight at Age Females: Age 2: 34 cm / 0.8 kg Age 3: 42 cm / 1.4 kg Age 4: 50 cm / 2.3 kg Males: Age 2: 33 cm / 0.7 kg Age 3: 41 cm / 1.3 kg Age 4: 48 cm / 2.0 kg 336 748 424 1439 331 716 411 1318 336 748 424 1439 331 716 411 1318

    8. Maturity

    9. Maturity and Spawning dynamics Higher female growth rate is relative after the onset of maturity Males slow proportionally down Changes in spawning seasonality, probably due to flooding regimes Probably, extended spawning season from early spring to summer

    10. Summary: Life History Carp Fast growth (based on 2 annuli per year) Early maturity Extended spawning season >>> Typical life history traits of successful invaders!!!

    11. 3. Post-impoundment trends 1971-1976 and 2007-2008

    12. Gillnet survey (Hamman) Summer 1972 – Winter 1976 Mesh sizes: 44, 64, 76, 89, 102, 114, 146 mm CPUE (76-146mm panels) = Standardised to kg fish per 100m gillnet night Gillnet survey (Present) June 2007 and January 2008 Mesh sizes: 44, 60, 75, 100, 144 mm CPUE (75-144mm panels) Standardised to kg fish per 100m gillnet night >> Fleet correction factor 44 64 76 89 102 114 146 44 64 76 89 102 114 146

    13. Accounting for Selectivity Estimating Gillnet selectivity SELECT method in R (Miller and Holst 1997) Estimates k1 and k2 Predict population length frequency Hamman vs. Present Parametric Bootstrapping for catch simulation Comparison of relative weight in the catch Correction Factor for Selectivity E.g. 1.09 for mudfish Fleet fact. x Selection fact. = Total correction factor

    14. Post-impoundment trendsStandardised CPUE Initial colonization: Carp most abundant species Sm Yellowfish hardly existent (CPUE=0.1 kg / net night), slow population increase from Winter 1974 Moggel initially abundant, but declining ~ 35 years later Population explosions Sm Yellow (CPUE = 30 kg/net night) and Mudfish (CPUE = 17.5 kg / net night) in Summer 2008 Lm Yellow slightly increased Carp decreased Moggel almost disappeared!!!

    15. 4. Lake Gariep Food web d13C and d15N Stable Isotope analysis

    16. Lake Gariep foodwebFish community

    17. Food web structure

    18. Food web structure

    19. Food web structure

    20. Food web structure

    21. Food web structure

    22. Conclusion Common carp could not out compete the endemic riverine species Smallmouth yellowfish (L. aeneus) and mudfish (L.capensis) in the turbid lacustrine system of Lake Gariep Limited conservation threat in Lake Gariep Reasons: Endemic species are adapted to turbid conditions of the Orange River Carp habitat probably limited to shallow muddy bays Limited food sources

    23. Thank You!

    24. Acknowledgements A big thank you to James and Helen Carey for their support and hospitality at Oviston Reserve, to the Gariep Fish Hatchery staff, and the Free State Nature Conservation Thanks to the support EP Freshwater Bank Angling Federation, in particular Barry Kurton, to the NC and FS Police Anglers and to the National SA Freshwater Bank Angling Association. Thanks to all the students from DIFS who helped us sampling. Project funding and bursary is provided by the National Research Foundation (FA2005021600012)

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