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Crawford R.J.M.,Oceans and Coasts | Crawford R.J.M.,University of Cape Town | Dyer B.M.,Oceans and Coasts | Geldenhuys D.,Cape Nature | And 5 more authors.
African Journal of Marine Science | Year: 2012

During 2008-2012, the number of crowned cormorants Phalacrocorax coronatus breeding in South Africa was c. 1 900 pairs, compared to 1 700 pairs for 1977-1981. Numbers at 10 islands in the Western Cape province fluctuated around a level of 1 100 pairs from 1991/1992 to 2011/2012, 300 more than from 1978/1979 to 1990/1991. These increases are attributable to the discovery of more colonies and an increased frequency of counting at the 10 islands after 1990/1991. The overall number of crowned cormorants breeding in South Africa is thought stable in the long term. Crowned cormorants feed mainly on small, inshore fish species that are not harvested by humans. Clinidae dominated the diet at 10 colonies adjoining the open sea, whereas Gobiidae contributed most food of birds at three colonies in a lagoon. The stability of the crowned cormorant population contrasts with decreases of some other seabirds endemic to southern Africa that feed primarily on prey that is exploited by fisheries. The crowned cormorant population decreased in the Northern Cape and small numbers initiated breeding at colonies to the east of Cape Agulhas at the turn of the century, but most of the population continues to breed to the west of Cape Agulhas. In some instances the availability of suitable breeding habitat may limit numbers breeding. © 2012 Copyright NISC (Pty) Ltd.

Crawford R.J.M.,Oceans and Coasts | Crawford R.J.M.,University of Cape Town | Altwegg R.,University of Cape Town | Altwegg R.,South African National Biodiversity Institute | And 14 more authors.
African Journal of Marine Science | Year: 2011

The number of African penguins Spheniscus demersus breeding in South Africa collapsed from about 56 000 pairs in 2001 to some 21 000 pairs in 2009, a loss of 35 000 pairs (>60%) in eight years. This reduced the global population to 26 000 pairs, when including Namibian breeders, and led to classification of the species as Endangered. In South Africa, penguins breed in two regions, the Western Cape and Algoa Bay (Eastern Cape), their breeding localities in these regions being separated by c. 600 km. Their main food is anchovy Engraulis encrasicolus and sardine Sardinops sagax, which are also the target of purse-seine fisheries. In Algoa Bay, numbers of African penguins halved from 21 000 pairs in 2001 to 10 000 pairs in 2003. In the Western Cape, numbers decreased from a mean of 35 000 pairs in 2001-2005 to 11 000 pairs in 2009. At Dassen Island, the annual survival rate of adult penguins decreased from 0.70 in 2002/2003 to 0.46 in 2006/2007; at Robben Island it decreased from 0.77 to 0.55 in the same period. In both the Western and Eastern Cape provinces, long-term trends in numbers of penguins breeding were significantly related to the combined biomass of anchovy and sardine off South Africa. However, recent decreases in the Western Cape were greater than expected given a continuing high abundance of anchovy. In this province, there was a south-east displacement of prey around 2000, which led to a mismatch in the distributions of prey and the western breeding localities of penguins. © NISC (Pty) Ltd.

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