State of the Bay Report 2010-Final - Anchor Environmental

Anchor Environmental
took 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 1980’s.
The 2010 sampling event recorded comparable data to earlier surveys in Big Bay and Small
Bay with clear reductions in the abundance of some species. In Langebaan lagoon, the 2010
sampling revealed the highest densities of white stumpnose and harder juveniles yet recorded in all
the annual seine net sampling conducted to date. This reflects natural and human induced
variations in the adult population size, recruitment success and use of the near shore habitat by fish
species; but may also be a result of the benefits of protection from exploitation and reduced
disturbance at some sites due to the presence of the Langebaan MPA. Certainly the study by
Kerwath et al. (2009) demonstrated the benefits of the MPA for white stumpnose and the protection
of harders from net fishing in the MPA undoubtedly benefits the stock. Although correlation should
not be interpreted as cause and effect, it is notable that white stumpnose density recorded during
2010 was higher than the long-term average at sites further away from anthropogenic disturbance
(Lagoon and North Bay sites), whilst densities decreased at most Small Bay and Big bay sites. The
presence and proposed expansion of heavy industrial activity, increased urbanization and associated
pollutants entering the Bay system as well as future large scale dredging and port expansion plans
undoubtedly places strain on the supporting environment and ecosystem, whilst increased human
exploitation places direct pressure on fish stocks. 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. The diversity of birds utilising
Saldanha Bay and the islands are considered low, however, this region supports substantial
proportions of the total population of many of these species. Regular surveys of breeding
populations of these birds have been conducted.
Annual counts of breeding African Penguin pairs indicate that there has been an overall
decrease in population size at all four islands in the Bay (Malgas, Marcus, Jutten and Vondeling). The
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 2 049 breeding pairs in 1987 to 506 breeding pairs in
2010, representing a 75% decrease in 24 years. This trend currently shows no sign of reversing, and
immediate conservation action is required to prevent further declines.
Populations of Kelp Gulls showed steady year-on-year increases in 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 species Mytilus galloprovincialus. 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 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
three years.
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 28