State of the Bay Report 2010-Final - Anchor Environmental

Anchor Environmental
increase in Oystercatcher numbers over the past two decades is due primarily to the introduction
and proliferation of the alien mussel Mytilus galloprovincialis, as well as due to the enhanced
protection of this species throughout much of its range (Loewenthal in prep.).
African Black Oystercatchers are resident on the islands, feeding in the rocky intertidal.
While the mussels arrived and became important in the diet between the late 1980s and the early
1990s, the effects on population only began to show much later because of the age at first breeding
and slow breeding rate of these birds (Hockey 1983). The population has stabilised in the recent
years and the carrying capacity of the islands has probably been reached (Loewenthal in prep.).
Oystercatchers are unlikely to be affected by water quality in Saldanha Bay except in as much as it
affects intertidal invertebrate abundance. Like most of the birds described above, they are,
however, vulnerable to catastrophic events such as oil spills.
Number of breeding pairs
600
500
400
300
200
100
0
1976
1978
1980
1982
1984
Total
Marcus
Malgas
Jutten
1986
1988
1990
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 246
1992
Figure 11.10. Trend in breeding population of African Black Oystercatchers older than 1 year, on Marcus,
Malgas and Jutten Islands in Saldanha Bay. (Data source: Douglas Loewenthal, Oystercatcher
Conservation Programme).
Year
1994
1996
1998
2000
2002
2004
2006
2008
2010