African penguins as predators and prey — coping (or not) with change

  • RJM Crawford Marine & Coastal Management, Private Bag X2, Rogge Bay 8012, South Africa
  • JHM David Marine & Coastal Management, Private Bag X2, Rogge Bay 8012, South Africa
  • LJ Shannon Marine & Coastal Management, Private Bag X2, Rogge Bay 8012, South Africa
  • J Kemper University of Namibia, Private Bag 13301, Windhoek, Namibia
  • NTW Klages Port Elizabeth Museum, P.O. Box 13147, Humewood 6013, South Africa
  • J-P Roux Ministry of Fisheries and Marine Resources, P.O. Box 394, Lüderitz, Namibia
  • LG Underhill Avian Demography Unit, University of Cape Town, Rondebosch 7700, South Africa
  • VL Ward Western Cape Nature Conservation Board, Private Bag X100, Vlaeberg 8018, South Africa
  • AJ Williams Western Cape Nature Conservation Board, Private Bag X100, Vlaeberg 8018, South Africa
  • AC Wolfaardt Western Cape Nature Conservation Board, Private Bag X100, Vlaeberg 8018, South Africa

Abstract

African penguins Spheniscus demersus live in the Benguela and western Agulhas ecosystems off southern Africa. Their numbers decreased throughout the 20th century from at least 1.5 million to about 0.18 million adults, although different regional trends were apparent. They feed to a large extent on shoaling epipelagic fish, notably anchovy Engraulis capensis and sardine Sardinops sagax, and regional trends in the abundance of penguins are associated with trends in the abundance and distribution of these prey fish. Many first-time breeders emigrate from colonies where feeding or other conditions at the time are unfavourable to more favourable breeding localities. This has led to both the extinction and formation of colonies. Food now may limit colonies at relatively small sizes, a fact attributable to industrial fisheries reducing the densities of forage fish. African penguins share their habitat with several other predators, with which they compete for food and breeding space. One of these, the Cape fur seal Arctocephalus p. pusillus, increased through the 20th century to 1.5–2 million animals at its close. Reported observations of predation by fur seals on seabirds have increased in recent decades and threaten the continued existence of small colonies of penguins. Stochastic modelling suggests that colonies of 10 000 pairs have a 9% probability of extinction in 100 years, so smaller populations should be regarded as “Vulnerable”. However, in a period of prolonged food scarcity off southern Namibia, the regional population decreased from more than 40 000 pairs in 1956 to about 1 000 pairs in 2000, and many colonies numbering less than 1 000 pairs became extinct. The minimum viable population for African penguins is currently considered to be >40 000 pairs, likely of the order of 50 000 pairs, a figure equivalent to its level in 2000. The chance of survival of the species through the 21st century is tenuous.

African Journal of Marine Science 2001, 23: 435–447
Published
2006-10-23
Section
Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X