Trends in numbers of Cape Cormorants (Phalacrocorax capensis) over a 50-year period, 1956–57 to 2006–07
Robert J. M. Crawford A B E , Bruce M. Dyer A , Jessica Kemper C , Robert E. Simmons D and Leshia Upfold AA Department of Environmental Affairs and Tourism, Marine and Coastal Management, Private Bag X2, Rogge Bay 8012, South Africa.
B Avian Demography Unit, Department of Statistical Sciences, University of Cape Town, Rondebosch 7701, South Africa.
C African Penguin Conservation Project, PO Box 586, Lüderitz, Namibia.
D Percy FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa.
E Corresponding author. Email: crawford@deat.gov.za
Emu 107(4) 253-261 https://doi.org/10.1071/MU07015
Submitted: 27 February 2007 Accepted: 22 August 2007 Published: 5 December 2007
Abstract
The population trend of Cape Cormorants (Phalacrocorax capensis), a species endemic to southern Africa and that feeds mainly on shoaling pelagic fish, is described for a 50-year period, from 1956–57 to 2006–07. The main breeding localities for the species are grouped in three regions in the Benguela upwelling ecosystem: guano platforms off central Namibia, islands off southern Namibia and islands off South Africa’s Western Cape Province. From 1956–57 to 1978–79, the numbers breeding off Namibia increased, as a result of increased availability of breeding space and adequate supplies of food. In the same period, numbers remained stable in the Western Cape. Numbers decreased off southern Namibia in the early 1980s and off central Namibia in the early 1990s, when environmental perturbations reduced the availability of food. Numbers decreased in the Western Cape in the early 1990s, following periods of scarcity of anchovy (Engraulis encrasicolus), an important prey item, and an outbreak of avian cholera caused by the bacterium Pasteurella multocida. They remained low as cholera outbreaks continued and some pelagic fish were displaced to the east beyond the foraging range of breeding Cormorants. The overall population of Cape Cormorants was of the order of 100 000 pairs in 1956–57, increased to ~250 000 pairs in the 1970s, but reverted to ~100 000 pairs in 2005–06.
Additional keywords: avian cholera, environmental perturbation, food, guano, population trend.
Acknowledgements
We thank our research institutes (listed under addresses) and the National Research Foundation for supporting this research. We are grateful to all who assisted with surveys of Cape Cormorants, to B. L. Dundee and F. V. Velho for arranging surveys of the Namibian platforms and Ilha dos Tigres, and to W. Groenewald, D. Klein and J. Klein for providing information on the guano platforms. CapeNature, Department of Environmental Affairs and Tourism (South Africa), Ministry of Fisheries and Marine Resources (Namibia), Robben Island Museum, South African National Parks and South African Navy provided logistical support for the surveys. This paper is a contribution to the project LMR/EAF/03/02 of the Benguela Current Large Marine Ecosystem (BCLME) Program. We are grateful to three referees, whose comments resulted in considerable improvement of the paper.
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