Page 284 - Atlas Sea Birds Ver1

2.3.2 Breeding localities and pup production of Cape Fur Seals
in Namibia

Authors: DN Mwaala, L Nghimwatya, BNS Tjandja, and I Kaholongo

Abstract:
Cape Fur Seals (Arctocephalus pusillus pusillus) have bred at 29 localities in Namibia, of which 26 were extant in 2018. Brief descriptions
of the localities are given, which include their conservation status and the utilisation of seals through harvesting and ecotourism. The
numbers of pups counted on aerial photographs of the colonies from 16 surveys undertaken between 1972 and 2018 are listed. Overall
numbers of pups born in Namibia fluctuated around a level of about 150,000 between 1972 and 2002 and then increased to about 300,000 in
2018. In the same period there was a northward shift in the distribution of pups: in 1972 63% of pups were born south of Lüderitz, whereas
in 2018 71% were born north of Walvis Bay.
Introduction:
The Cape Fur Seal (Arctocephalus pusillus pusillus) is the only resident, breeding pinniped off southern Africa. It breeds in dense colonies
on islands, islets and the mainland coast from Baía dos Tigres in Angola, through Namibia to Black Rocks in Algoa Bay, South Africa. Cape
Fur Seals are abundant and they historically inhabited most, if not all, islands in Namibia and South Africa (Shaughnessy 1978). However,
extensive, uncontrolled and indiscriminate harvesting that took place between the 18th and the early part of the 20th centuries in Namibia
and South Africa greatly reduced their population and extirpated colonies at many islands (Shaughnessy 1978, David 1989). Following
the introduction of harvesting controls, the population showed fluctuating growth, increasing in the 1940s (Shaughnessy 1978) and the
1970s and 1980s (Kirkman et al. 2013). It was then stable through the 1990s and 2000s (Kirkman et al. 2013). The increase in the 1940s
included the formation of new colonies and displacement of seabirds from some islands (Shaughnessy 1984). Birds were also displaced
from Mercury Island in the 1980s (Crawford et al. 1989).
Cape Fur Seals spend most of their lives at sea and hence cannot be directly censused like several terrestrial mammals. Aerial censuses
conducted during the peak of their breeding (mostly around 17–21 December) were used to estimate numbers of pups produced in the
region. The first aerial censuses were conducted in 1971 and 1972 (Shaughnessy 1987, Kirkman et al. 2007). In Namibia, the results
of the aerial censuses have been used as the basis of the population assessment, and to recommend a sustainable harvest, of seals.
Cape Fur Seals are an important component of the Benguela ecosystem, mostly as an apex predator. However they also fall prey to
marine and coastal predators such as the great white (Carcharodon carcharias) and other sharks and Killer Whales (Orcinus orca) (Ham-
merschlag et al. 2006, Fallows et al. 2016). Several terrestrial predators, e.g. Black-backed Jackals (Canis mesomelas), Brown Hyenas
(Parahyaena brunnea) (Kuhn et al. 2008; Wiesel 2006, 2010) and desert Lions (Panthera leo) (Stander 2019), feed on Cape Fur Seal
pups at mainland colonies. The diet of the Cape Fur Seal has been studied extensively, formerly using stomach contents (David 1987a,
b, Castley 1991) and more recently scats (Mecenero 2006a, b, de Bruyn et al. 2003). Their primary prey items were small- and medium-
sized epi- and meso-pelagic fish. Five teleost prey groups dominated their diet: bearded goby (Sufflogobius bibarbatus), lanternfish
(Lampanyctodes hectoris), Cape horse mackerel (Trachurus capensis), juvenile Cape hake (Merluccius capensis) and three clupeiods:
anchovy (Engraulis capensis), round herring (Etrumeus whiteheadi) and sardine (Sardinops sagax) (Mecenero 2006a, b, Mwaala 2022).
Crustaceans, such as West Coast (Cape) rock lobster (Jasus lalandii), and cephalopods, such as the squid (Loligo vulgaris reynaudii),
also featured in their diet (de Bruyn et al. 2003, Mwaala 2022), which varies spatially and temporally (Mecenero 2006a, b, Mwaala 2022).
Several Cape Fur Seal colonies in southern Namibia are free from human disturbance as they are found in either a National Park or
proclaimed diamond areas that restrict human access. Entanglements in marine debris, mostly fishing lines, are a threat to Cape Fur
Seals (Curtis et al. 2021).

Management and conservation new markets and diversification of seal products, the
The Cape Fur Seal first received protection in 1893 pup harvest increased during the 1990s. The Sea Birds
under the Fish Protection Act of the then Cape Colony and Seal Protection Act of 1973 was repealed by the
(Shaughnessy 1984), which required a permit for harvesting Sea Fisheries Act 29 of 1992. In Namibia, this was later
of seals. In 1909, the sealing season was limited to prevent replaced by Namibia’s Marine Resource Act of 2000, under
disturbance during the breeding season (David 1989). which a rolling, three-year Total Allowable Catch (TAC)
There followed the Sealing and Fisheries Proclamation of was introduced.
1922 and the Sealing and Fisheries Ordinance of 1949. In The harvesting season, which commenced on
1973, the 1893 Act and the 1949 Ordinance were replaced 1 August was brought forward to 1 July and closed
st
st
by South Africa’s Sea Birds and Seals Protection Act, on 15 November at the onset of the seal breeding season.
th
which empowered the Minister to prescribe the age, size In 2021, commercial harvesting of seals took place at
and sex of seals harvested, as well as the season and four mainland colonies in Namibia: Cape Cross and Torra
area of harvest. These measures led to a rapid recovery of Bay in the north and Atlas Bay and Wolf Bay in the south.
the Cape Fur Seal population towards the end of the 20th
century. Numbers of pups born
However, despite the growth in numbers, seals failed to Numbers of pups counted on aerial photographs of 26
re-colonize some of the islands they previously inhabited, colonies taken on 16 surveys conducted between 1972
which was believed to be caused by human presence at and 2018 are shown in Table 1. Data from 1971–2004 were
those islands. Although a quota management system from Kirkman et al. (2007), who for that period also listed
was introduced in 1974, in the 1980s the number of seals pup counts at some colonies in years having less complete
harvested was fairly irregular, due to the collapse of the surveys, which are not indicated on Table 1. No counts of
international market for pelts. Following identification of pups were made at Seal Island (Lüderitz) between 1971

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