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

Number of breeding pairs
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
State of Saldanha Bay & Langebaan Lagoon 2011
Birds
Hartlaub's Gull, Larus hartlaubii, is about the 10th
rarest of the world's roughly 50 gull species. It is endemic to
southern Africa, occurring along the West Coast from
Swakopmund to Cape Agulhas. It breeds mainly on
protected islands but has also been found to breed in
sheltered inland waters. Hartlaub’s Gulls are relatively
nomadic, and can alter breeding localities from one year to
the next (Crawford et al. 2003).
The numbers breeding on the different islands are
highly erratic, as are the total numbers in the Bay. The
highest and most consistent numbers of breeding birds are
found on Malgas, Jutten and Schaapen islands, with a few birds breeding Vondeling Island between
1991 and 1999. They have also been recorded breeding on Meeuw Island in 1996 and from 2002 to
2004. There are substantial inter-annual fluctuations in numbers of birds breeding, suggesting that in
some years an appreciable proportion of the adults do not breed (Crawford et al. 2003). Natural
predators of this gull are the Kelp Gull, African Sacred Ibis and Cattle Egret, which eat eggs, chicks
and occasionally adults (Williams et al. 1990). In Saldanha Bay there is no discernable upward or
downward trend over time, but there is some concern in that breeding has ceased at Schaapen
Island and overall numbers have remained very low for the past four years (Figure 10.3).
3500
3000
2500
2000
1500
Hartlaub's Gull
total
Vondeling
Malgas
Jutten
Marcus
Schaapen
Meeuw
Caspian Is.
1000
500
0
Figure 10.3. Trends in breeding population of Hartlaub’s Gulls at Malgas, Marcus, Jutten, Schaapen and
Vondeling Islands in Saldanha Bay (Data source: Rob Crawford, DEA: Oceans & Coasts).
Year
The Swift Tern, Sterna bergii, is a widespread species that occurs as a common resident in
southern Africa. Swift Terns breed synchronously in colonies, usually on protected islands, and often
in association with Hartlaub’s Gulls. Sensitive to human disturbance, their nests easily fall prey to Kelp
Gulls, Hartlaub’s Gulls and Sacred Ibis (Le Roux 2002). During the breeding season, fish form 86% of
all prey items taken, particularly pelagic shoaling fish, of which the Cape Anchovy (Engraulis
encrasicolus) is the most important prey species. Since 2001 there has been an increase in the Swift
Tern population number in South Africa. This increase coincided with a greater abundance of two of
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