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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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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)