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Marine Ecology Progress Series

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MEPS 552:241-253 (2016)  -  DOI:

An integrated mark-recapture and genetic approach to estimate the population size of white sharks in South Africa

Sara Andreotti1, Michael Rutzen2, Stéfan van der Walt3, Sophie Von der Heyden1, Romina Henriques1, Michael Meÿer4, Herman Oosthuizen4, Conrad A. Matthee1,*

1Evolutionary Genomics Group, Department of Botany and Zoology, Private Bag X1, Stellenbosch University, Stellenbosch 7600, South Africa
2Shark Diving Unlimited, Kleinbaai, Gansbaai 7220, South Africa
3Applied Mathematics, Stellenbosch University, Matieland 7602, South Africa
4Department of Environmental Affairs, Branch Oceans and Coasts, Private Bag X2, Roggebaai 8012, South Africa
*Corresponding author:

ABSTRACT: The loss of apex marine predators has been reported to have a cascade of detrimental effects on marine ecosystems; however, the general lack of empirical data can severely limit our understanding of the ecological interactions among marine species. In this study we propose an integrated approach using mark-recapture and genetic techniques to assess population estimates of white sharks Carcharodon carcharias. Between 2009 and 2011, 4389 dorsal fin photographic identifications were collected in Gansbaai, South Africa, from 426 white sharks and used in mark-recapture analyses. Saturation of new sightings occurred once 400 individuals were catalogued and the open population model POPAN suggested ranges between 353 and 522 individuals (95% confidence) and a point estimate of N = 438. Between 2010 and 2013, 302 biopsy samples were collected from 233 white sharks and used for a comparative genetic population estimate. Analyses of 14 microsatellite markers revealed a contemporary effective population size (CNe) of 333 individuals (95% CI = 247-487, pcrit = 0.02). These values were at least 52% less than those estimated in previous mark-recapture studies. Using this combination of techniques, we propose a Ne:N ratio of 0.76 for white sharks, which advances our ability to accurately make inferences on elasmobranch population numbers in general. Given the low population numbers of white sharks along the South African coastline, we predict a negative effect on the ecological stability of the marine environment in this region.

KEY WORDS: Carcharodon carcharias · Effective population size · Microsatellites · Photographic identification · Population abundance · Shark conservation

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Cite this article as: Andreotti S, Rutzen M, van der Walt S, Von der Heyden S and others (2016) An integrated mark-recapture and genetic approach to estimate the population size of white sharks in South Africa. Mar Ecol Prog Ser 552:241-253.

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