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

Number of breeding pairs
State of Saldanha Bay & Langebaan Lagoon 2011
Birds
2500
African Penguin
2000
Total
Malgas
1500
1000
Marcus
Jutten
Vondeling
500
0
Figure 10.1. Trends in African Penguin populations at Malgas, Marcus, Jutten and Vondeling islands in
Saldanha Bay (Data source: Rob Crawford, DEA: Oceans & Coasts).
Year
There is considerable uncertainty around the cause of the decreases, however. One of the
measures currently being employed to curb these declines is the use of no-take zones for purseseine
fishing. This strategy, recently tested at St Croix Island in the Eastern Cape, was effective in
decreasing breeding penguins’ foraging efforts by 30% within three months of closing a 20 km zone
to purse-seine fisheries (Pichegru et al. 2010). In this case the use of small no-take zones has
represented immediate benefits for a top predator dependent on pelagic prey, with minimum cost
to the fishing industry, while protecting ecosystems within these habitats and important species.
However, research at Dassen and Robben Islands has not delivered such positive results.
The reduction in colony sizes at most of the islands in Saldanha Bay will have had severe
negative consequences for penguins. When Penguins breed in large colonies, packed close to one
another, they are better able to defend themselves against egg and chick predation by Kelp gulls.
Also, these losses are trivial at the colony level. However, the fragmented colonies and the massive
rise in gull numbers associated with the rapidly expanding human settlements in the area, means
that gull predation is increasingly problematic. Similarly, predation by seals (on land and around
colonies) is having an increasingly negative impact on these dwindling colonies (Makhado et al.
2009). Additional stress, such as turbidity and increased vessel traffic, will not only impact penguins
directly, but is likely to influence the location of schooling fish that the penguins are targeting and
their ability to locate these schools. There are also concerns that toxin loads influence individual
birds’ health, reducing their breeding success and/or longevity (Game et al. 2009).
In summary, the initial collapse of the penguin colonies in the area is probably related to
food availability around breeding islands and in areas where birds not engaged in breeding are
foraging. However, now that colonies have shrunk so dramatically, the net effect of local conditions
at Saldanha Bay are believed to be an increasingly important factor in the continued demise of
African penguin colonies at the islands.
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