Influences of the abundance and distribution of prey on African penguins Spheniscus demersus off western South Africa

  • RJM Crawford Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Rogge Bay 8012, South Africa; Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa
  • LG Underhill Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa
  • JC Coetzee Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Rogge Bay 8012, South Africa
  • T Fairweather Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa
  • LJ Shannon Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa
  • AC Wolfaardt Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa; CapeNature, Private Bag X5014, Stellenbosch 7599, South Africa

Abstract

Off South Africa, anchovy Engraulis encrasicolus and sardine Sardinops sagax are the main prey of African penguins Spheniscus demersus. The combined spawner biomass of these fish increased from less than one million t in 1996 to more than nine million t in 2001 and then decreased to four million t in 2005. The combined biomass of young-of-the-year of these species increased from 0.2 million t in 1996 to 3.2 million t in 2001 before falling to 0.4 million t in 2005. There was a large eastward shift in the distribution of sardine between 1999 and 2005. The number of African penguins breeding in the Western Cape Province increased from 18 000 pairs in 1996 to more than 30 000 pairs from 2001 to 2005 before falling to 21 000 pairs in 2006, as the availability of fish decreased near breeding localities. Numbers of penguins breeding and numbers of birds in adult plumage moulting were significantly correlated with the young-of-the-year biomass of anchovy and sardine and with the available biomass of spawning sardine. The increase in the number of penguins breeding was mainly attributable to a greater proportion of birds breeding and improved breeding success. The decrease probably resulted from high mortality. Delayed first breeding and abstinence from breeding during periods of food shortage may both increase survivorship when food is scarce and enable seabirds rapidly to take advantage of improved feeding conditions. Although long-lived seabirds are buffered against short-term variability in food supplies, environmental change that influences the abundance and availability of prey can have severe consequences for central-place foragers, such as penguins, if there is long-term displacement of prey to regions where no suitable breeding localities occur.

Keywords: African penguin; breeding proportion; breeding success; food; mortality; Spheniscus demersus

African Journal of Marine Science 2008, 30(1): 167–175
Published
2008-06-25
Section
Articles

Journal Identifiers


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