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

State of Saldanha Bay & Langebaan Lagoon 2011
Executive Summary
place (i.e. 1970s-1980s), and as no fish sampling took place over this period, these are not reflected
in the available data which only exists from the late 1980s.
The 2011 sampling event recorded remarkably good harder recruitment throughout the
Saldanha Bay-Langebaan Lagoon system, whilst the estimated abundance of other key species such
as white stumpnose, gobies and silversides within Big Bay and Langebaan Lagoon compare
favourably with data from earlier surveys. In Small Bay, however, where the average density of
commercially-important fish such as white stumpnose have always been traditionally much higher
than other areas of the bay (e.g. white stumpnose density in Small Bay = 0.8 fish.m -2 vs. 0.1 fish.m -2
in Big Bay and 0.05 fish.m -2 in Langebaan lagoon), there were clear reductions in the abundance of
this and other key species (with the exception of harders), with the lowest yet recorded black tail
density and the second lowest white stumpnose density to date. This follows the trend observed in
the 2010 report. The fact that the abundance of key species are declining in the area of maximum
anthropogenic disturbance (Small Bay), while they are increasing in other less-disturbed areas (Big
Bay and Langebaan Lagoon) is very telling and naturally of some concern. Ongoing, regular
monitoring of the ichthyofauna and fisheries in Saldanha Bay and Langebaan Lagoon is therefore
strongly recommended.
Birds
Saldanha Bay, Langebaan Lagoon and the associated islands provide important shelter, feeding and
breeding habitat for at least 53 species of seabirds, 11 of which are known to breed on the islands.
The islands of Malgas, Marcus, Jutten, Schaapen and Vondeling support breeding populations of
African Penguin (a red data species), Cape Gannet, four species of marine cormorants, Kelp and
Hartlaub’s Gulls, and Swift Terns. The islands also support important populations of the rare and
endemic African Black Oystercatcher. Saldanha Bay and its islands support substantial proportions
of the total populations of several of these species.
There has been an overall decrease in the breeding population of African Penguin at all four
islands in the Bay (Malgas, Marcus, Jutten and Vondeling). This decrease in numbers has been
attributed to migration to other islands (Robben and Dassen Islands) and a reduced availability of
anchovy, which is the primary food source for these birds. The population in Saldanha Bay has
decreased from 2049 breeding pairs in 1987 to 506 breeding pairs in 2010, representing a 75%
decrease in 24 years. Although penguin numbers in Saldanha Bay in 2011 are slightly up on that in
2010 (614 vs. 506 pairs), the overall downward trend currently shows no sign of reversing, and
immediate conservation action is required to prevent further declines.
Populations of Kelp Gull have showed steady year-on-year increases in the Saldanha Bay
region until 2000, most likely due to the increase in availability of food as a result of the introduction
and spread of the invasive alien mussel Mytilus galloprovincialis. Since 2000, however, populations
on the islands have been steadily decreasing, following large-scale predation by Great White
Pelicans Pelecanus onocrotalus that was first observed in the mid-1990s. During 2005 and 2006,
pelicans caused a total breeding failure of Kelp Gulls at Jutten and Schaapen Islands, the effects of
which are still apparent in 2010.
Hartlaub’s Gull and Swift Tern populations vary erratically, with numbers fluctuating widely
each year. There have been no long-term increases or decreases in populations of these birds.
There is some concern, though, that Swift terns have not bred on any of the islands in the bay for
four years now.
Populations of Cape Gannets and Cape Cormorants also vary each year. Cape Gannets on
the West Coast have been declining since the start of an eastward shift of pelagic fish stocks in the
late 1990’s. This is, to some extent, compensated for by an increase in the numbers of breeding
birds on the east coast (Bird Island). Recent increases in predation by Cape fur seals Arctocephalus
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