Page 468 - Atlas Sea Birds Ver1

Numbers of Kelp Gulls breeding in South Africa
increased from about 10,000 pairs in 1976–1980 to
c. 21,100 pairs from 2000–2005 and then decreased to
17,600 pairs from 2009–2014 (Whittington et al. 2016).
The sum of the maximum count at each colony made
during 2018–2022 was c. 14,000 pairs and the sum of
the most recent count at each locality c. 12,750 pairs
(Table 2). These values show that the South African
population has continued to decrease since its peak at
the start of the present century. The increase in the late
20 century followed cessation of controls on Kelp Gulls Kelp Gulls (photo L Upfold)
th
at islands off western South Africa in the 1970s and was
associated with supplementary food provided by fish (Witteveen 2015). First-year survival was thought to benefit
factories and rubbish tips (Steele 1992, Crawford et al. from supplementary food provided at fishing harbours and
2009). The decreases resulted from predation of gull chicks refuse dumps (Steele and Hockey 1990). After breeding,
at some colonies by Great White Pelicans (Pelecanus adults dispersed from colonies to feeding sites (Martin
onocrotalus). Kelp Gulls responded to predation by pelicans and Baird 1987, Crawford et al. 1997, Whittington et al.
by decreasing densities of nests at islands where they 2006a) but tended to remain within regions (Altwegg et al.
were being fed upon, increasing clutch size, and moving to 2007, Whittington et al. 2009). First-year birds undertook
alternative sites, often mainland sites, to breed (Crawford longer movements (Altwegg et al. 2007, Whittington et al.
et al. 2009, Whittington et al. 2016). After 1982, there was 2009). Birds from southwest and central-south South Africa
an increase in numbers breeding in southern South Africa dispersed as far as central Namibia and KwaZulu-Natal,
(Whittington et al. 2006b) that matched eastward shifts in respectively (Underhill et al. 1999, Whittington et al. 2009).
the distributions of some prey species and several other A model showed that population growth was most
seabirds (Crawford et al. 2015). sensitive to changes in adult survival so conservation
The southern African population of Kelp Gulls increased efforts for the species, if needed, may have the highest
from c. 11,200 pairs in 1976–1981 (Crawford et al. 1982) impact if they targeted adults (Altwegg et al. 2007). Based
to c. 20,500 pairs in 2007 (Kemper et al. 2007) but was on the most recent counts, 16 of the Kelp Gull’s breeding
likely higher in the early 2000s, given the estimate of sites in southern Africa held ≥ 1% of the region’s population
21,000 pairs in South Africa then (Whittington et al. 2016). and hence should be regarded as important sites for the
The sums of the maximum counts at each locality were species. They were Ilha dos Tigres, Mile 4 saltworks,
c. 27,400 pairs in the 2000s and c. 20,000 pairs in the Halifax Island, Possession Island, Velddrif saltworks,
2010s (Table 2), but these may have overestimated the Jutten Island, Schaapen Island, Dassen Island, Robben
population if Kelp Gulls moved between breeding sites Island, Strandfontein coastline, Steenbras Dam, Dyer
during decades. The sum of maxima at colonies obtained Island, Keurbooms Lookout Beach, Keurbooms Peninsula,
from 2018–2022 was c. 14,200 pairs and the sum of the Swartkops River and Port of Ngqura (Table 2).
most recent counts at colonies was c. 16,000 pairs (Table 2), From 2000, the nests at Redhouse saltpan in the
confirming a decrease in the southern African population. Swartkops River were regularly raided by people removing
Counts made from 2010–2022 contributed 79% of the eggs and chicks. This resulted in some pairs moving to
sum of the most recent counts at colonies and from 2000– Brickfields Island. Eventually the Redhouse saltpan was
2009 18% of that total (Table 2). Kelp Gulls have reduced abandoned and the majority of those gulls bred at the
the productivity of threatened seabirds that are endemic Tippers Creek colony (Whittington et al. 2016, Martin
to BUS by eating their eggs and chicks, so measures to and Whittington 2024). In another example of movement
control their numbers have again been introduced at some between breeding sites, the Kelp Gull colony at the Coega
islands in Namibia and South Africa (e.g. Crawford and River saltpans relocated to the new Port of Ngqura from
Hockey 2005, Pichegru 2012). These will have contributed 2013, soon after the port was constructed (Martin and
to the decrease. Whittington 2024).
In addition to the harvests and disturbance by humans,
Conservation and management of southern African mainland colonies such as Keurbooms Lookout Beach,
Kelp Gulls which was washed away in 2007 (Witteveen 2024), and
Tippers Creek may be subject to flooding (Martin and
In southern Africa, most Kelp Gulls bred for the first time Whittington 2024) while, if water levels become too low,
when 4 years old (Crawford et al. 2000) and they fledged colonies at islands in estuaries or saltpans may be linked
up to 1.33 chicks per pair (Crawford and Hockey 2005). to the mainland, with associated disturbance and predation
At Keurbooms Peninsula breeding performance showed pressures. Kelp Gulls were killed by botulism and were
a positive relationship with vegetation cover and height susceptible to avian cholera (Pasturella multocida), which
(Witteveen 2015). The mean clutch size was 2.2 eggs, and may be contracted through scavenging on dead birds
the survival probability of birds in their first year was 0.44 (Crawford and Hockey 2005), and diseases such as highly
p.a., which increased to 0.84 p.a. for those aged one year pathogenic avian influenza (HPAI) (Khomenko et al. 2018).
and older (Altwegg et al. 2007).While incubating, Kelp Gulls Kelp Gulls were recorded as reservoirs of the zoonotic
spent more time foraging in natural than artificial habitats bacterias Campylobacter and Salmonella, some strains
(Reusch et al. 2020). Chicks were fed a smaller proportion of which were resistant to a variety of antimicrobial drugs
of anthropogenic food items than was eaten by adults (Moré et al. 2017).

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