Page 613 - Atlas Sea Birds Ver1

southern African islands were further plundered by sailors terns, the changed breeding distributions were concomitant
seeking Cape Fur Seal pelts (Randall 1989). By the start with decreases in the overall populations of the affected
of the 20 century, the seal population had been drastically predators (Crawford 2007, Crawford et al. 2015, 2022),
th
reduced by indiscriminate harvesting and was extinct at although recently numbers of Cape Cormorants recovered
23 of its former island colonies (Shaughnessy 1984, David on account of rapid growth of its northernmost colony in
1989). Fortunately for penguins, their meat was regarded southern Angola (Morais 2024a). Seabird species that
as unpalatable and described by shipwrecked sailors as were able to move their breeding location, had extensive
‘foul fare’ (Randall 1989) and, for seals, implementation foraging ranges when breeding, or were able to feed on
of harvest controls allowed a recovery of their population alternative food sources were not as severely affected by
in the 20 century (Mwaala et al. 2024, Seakamela et the prey shifts than those having less behavioural flexibility
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al. 2024). Intensive harvesting or disturbance of seals at (Pichegru et al. 2010, Crawford et al. 2014).
colonies may cause them to change their breeding locality
(Kruger 1949, Crawford et al. 1989). Eggs in one basket
White gold and golden eggs An outcome of the ‘emptying out’ of the central BUS and
movement of large numbers of some top predators towards
Pursuant to the hunting of seals and seabirds in the BUS, in its borders, was the congregation of substantial proportions
the mid-19 century several of their colonies were subjected of species at one or a few localities (Makhado et al. 2021).
th
to massive disturbance after the discovery of large deposits For example, in 2010 and 2020 Mercury Island held 72%
of guano at their breeding islands (Makhado et al. 2021). and 54% of the global population of Bank Cormorants
On account of its value as an agricultural fertiliser, seabird (Roux and Kemper 2015, Tom et al. 2024) and, in 2010,
guano was termed ‘white gold’ (Santana-Sagredo et al. 73% of Namibia’s African Penguins (Crawford et al. 2013).
2021). The islands were stripped of guano, causing birds In 2019, Bird Island in Algoa Bay, at the east of the BUS,
temporarily to seek alternative breeding grounds (Crawford had c. 70% of the overall population of Cape Gannets
et al. 1983) and in the longer term reducing the quality of (Sherley et al. 2019). Furthermore, in 2020, 54% of Cape
nesting habitat (Crawford and Cochrane 1990, Ross and Cormorants bred at Ilha dos Tigres at the north of the
Randall 1990). BUS (Morais 2024a). These colonies are of exceptional
The term ‘kill the goose that lays the golden eggs’ refers importance for conservation of the species concerned, but
to destroying that which provides income or advantage. also make large portions of their populations susceptible to
Unfortunately for African Penguins, although their flesh localised, catastrophic events such as oil spills, outbreaks
was disagreeable, their eggs were reportedly ‘extremely of disease, and severe weather (Makhado et al. 2021).
tasty’ (Randall 1989) and were reaped in an unsustainable
manner, thereby diminishing recruitment into the breeding Energy crisis
population and causing a huge decrease in numbers of
penguins in the first part of the 20 century (Shannon and The emptying of land-breeding predators out of the central
th
Crawford 1999). Collection of penguin eggs was terminated BUS was particularly evident for species, or subspecies,
in 1967 but further challenges lay ahead (Shelton et al. that competed with the region’s fisheries for prey (African
1984).
Penguin, Cape Gannet, Cape and Bank cormorants,
Inside out Greater Crested Tern, Cape Fur Seal), and it followed
collapses of three energy-rich forage resources in that
A remarkable feature of the BUS over the past 50 years region: sardine (Sardinops sagax), anchovy (Engraulis
was large-scale shifts in the distributions of several of encrasicolus), and rock lobster (Jasus lalandii) (Crawford
its land-breeding top predators, away from the system’s 2007, Crawford et al. 2008, 2014, Seakamela et al. 2024).
centre, between Hottentots Bay in south Namibia and Additionally, off west South Africa, the availability (per unit
St Helena Bay in west South Africa, towards its northern biomass) of sardine and anchovy to seabirds decreased in
and south-eastern borders (Kirkman et al. 2007, Makhado the present century (Crawford et al. 2019). In Namibia and
et al. 2021). In Namibia, increased proportions of African South Africa, seabirds that formerly depended on these
Penguins (Kemper 2015), Cape (Crawford et al. 2007b) nutritional resources were forced to seek food of inferior
and Bank (Roux and Kemper 2015) cormorants, and quality such as bearded goby (Sufflogobius bibarbatus)
Cape Fur Seals (Kirkman et al. 2007, Mwaala et al. 2024) and offal discarded by demersal fisheries (Grémillet et
bred in the north. For example, in 1972, 63% of Namibia’s al. 2008, Ludynia et al. 2010, Dyer et al. 2019, Erasmus
Cape Fur Seal pups were born south of Lüderitz, whereas et al. 2021). As summarised by Crawford et al. (2022), a
in 2018, 71% were born north of Walvis Bay (Mwaala et dearth of energy-rich prey reduced breeding participation,
al. 2024). Moreover, at the recent turn of the century both reproductive output, and immature and adult survival of
Cape Cormorants and seals started breeding in southern seabirds that competed with fisheries for prey, which led to
Angola (Dean et al. 2002, Mendelsohn and Haraes 2018). population decreases.
In South Africa, increased proportions of these four species In South Africa, there were also shifts to the south
and of Cape Gannet and Greater Crested Tern bred in the and east in the distributions of three seabirds that did
south and east of the BUS (Crawford et al. 2007a, 2008, not compete with fisheries for prey, White-breasted and
2011, 2016, Crawford 2009, Seakamela et al. 2024). Crowned cormorants, and Kelp Gull, which suggested
In both Namibia and South Africa, the altered use of some environmental forcing of the predator redistributions.
breeding localities by predators was associated with similar However, decreases of these species off northwest South
shifts in the distributions of key prey species (Crawford et Africa were less severe than those of sea birds that fed on
al. 2015, Seakamela et al. 2024). Except for seals and prey harvested by fisheries (Crawford et al. 2015).

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