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

• Published in: ICES journal of marine science 2007-04, Vol.64 (3), p.570-576
• Main Authors: Crawford, Robert J. M., Underhill, Les G., Upfold, Leshia, Dyer, Bruce M.
• Format: Article
• Language: English
• Subjects: African penguin; Arctocephalus pusillus pusillus; Cape fur seal; carrying capacity; density-dependence; fishing; food; Marine; recruitment; Spheniscus demersus
• ISSN: 1054-3139; 1095-9289
• DOI: 10.1093/icesjms/fsm009

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.