State of the Bay Report 2011-Final.pdf - Anchor Environmental

Number of breeding pairs
State of Saldanha Bay & Langebaan Lagoon 2011
Birds
Cape Cormorants Phalacrocorax capensis are endemic to
southern Africa, where they are abundant on the west coast but
less common on the east coast, occurring as far as Seal Island in
Algoa Bay. They breed between Ilha dos Tigres, Angola, and Seal
Island in Algoa Bay, South Africa. They generally feed within 10-15
km of the shore, preying on pelagic goby Sufflogobius bibarbatus,
Cape anchovy Engraulis capensis, pilchard Sardinops occelatus and
Cape horse mackerel Trachurus trachurus (du Toit 2004).
The Cape Cormorant is regarded as Near Threatened owing
to a decrease in the breeding population during the late 1970s
(Cooper et al. 1982). Numbers decreased again during the early
1990s following an outbreak of avian cholera, predation by Cape fur
seals and White Pelicans as well as the eastward displacement of
sardines off South Africa (Crawford et al. 2007). As a result there
are large inter-annual fluctuations in breeding numbers due to breeding failure, nest desertion and
mass mortality related to the abundance of prey, for which they compete with commercial fisheries.
This makes it difficult to accurately determine population trends. In addition, during outbreaks of
avian cholera, tens of thousands of birds die. Cape Cormorants are also vulnerable to oiling, and are
difficult to catch and clean. Discarded fishing gear and marine debris also entangles and kills many
birds. Kelp Gulls prey on Cape Cormorant eggs and chicks and this is exacerbated by human
disturbance, especially during the early stages of breeding, as well as the increase in gull numbers
(du Toit, 2004).
The Saldanha Bay population has been relatively stable since 1988, though with a fair
amount of interannual fluctuation (Figure 10.6). Numbers have generally been highest on Jutten
Island. Although no long term trends are discernable the population has not recovered to its 1993
level of over 23 000 breeding pairs.
30000
25000
20000
15000
Cape Cormorant
Total
Vondeling
Malgas
Jutten
Marcus
Schaapen
Meeuw
10000
5000
0
Figure 10.6. Trends in breeding population of Cape Cormorants at Malgas, Jutten, Schaapen, Vondeling and
Meeuw islands in Saldanha Bay (Data source: Rob Crawford, Oceans & Coasts, Department of
Environmental Affairs).
Year
225
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