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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on March 5, 2007
ICES Journal of Marine Science: Journal du Conseil 2007 64(3):570-576; doi:10.1093/icesjms/fsm009
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© 2007 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

An altered carrying capacity of the Benguela upwelling ecosystem for African penguins (Spheniscus demersus)

Robert J. M. Crawford1,2,, Les G. Underhill2, Leshia Upfold1 and Bruce M. Dyer1

1 Department of Environmental Affairs and Tourism, Marine and Coastal Management, Private Bag X2, Rogge Bay 8012, South Africa
2 Avian Demography Unit, Department of Statistical Sciences, University of Cape Town, Rondebosch 7701, South Africa

Correspondence to R. J. M. Crawford: tel: +27-21-4023140; fax: +27-21-4217406; e-mail: crawford{at}deat.gov.za

Crawford, R. J. M., Underhill, L. G., Upfold, L., and Dyer, B. M. 2007. An altered carrying capacity of the Benguela upwelling ecosystem for African penguins (Spheniscus demersus). – ICES Journal of Marine Science, 64: 570–576.

The carrying capacity of an ecosystem for a species is an input parameter that is required for some models that assess population viability. It may be changed by an altered structure or functioning of the ecosystem, e.g. as a consequence of changes brought about by fishing or environmental change. Hence, it cannot necessarily be assumed that the pristine level of abundance of a species reflects the present-day carrying capacity of the ecosystem for that species. Historical and modern information on abundance and density-dependent responses is used to investigate changes in the carrying capacity of the Benguela upwelling ecosystem for African penguins (Spheniscus demersus), a species categorized as vulnerable. The carrying capacity was estimated to decrease from 1.5–3.0 million adult birds in the 1920s to just 10–20% of this value from 1978 to 2006, as a result inter alia of increased competition for food with purse-seine fisheries and fur seals (Arctocephalus pusillus pusillus). From 1988/1989 to 2005/2006, the per capita recruitment of young penguins to a colony where nesting space was not limiting was inversely related to the size of that colony, suggestive of a density-dependent response perhaps related to food availability.

Keywords: African penguin, Arctocephalus pusillus pusillus, Cape fur seal, carrying capacity, density-dependence, fishing, food, recruitment, Spheniscus demersus

Received 1 November 2006; accepted 12 January 2007; advance access publication 5 March 2007.


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