Vagrant elephant seal predation on Cape fur seal pups, Plettenberg Bay, South Africa

Abstract

Vagrant southern elephant seals (Mirounga leonina) are occasionally sighted along the coast of South Africa and are known to feed primarily on fish and squid. Phocid seals are not known to predate on mammals making the events described here exceptional. This note describes the successful and failed attempts of a vagrant male southern elephant seal (M. leonina) to consume Cape fur seal (Arctocephalus pusillus pusillus) pups in Plettenberg Bay, South Africa. Observations were made by crew and passengers aboard a commercial whale-watching vessel during November 2012. This is the first account of elephant seals eating anything other than fish, squid and penguins and suggests considerable plasticity in prey choice dictated by environmental conditions.

Full text

SHORT NOTE
Vagrant elephant seal predation on Cape fur seal pups,
Plettenberg Bay, South Africa
Gwenith S. Penry •Ashwynn C. Baartman •
Martha
´n N. Bester
Received: 24 February 2013 / Revised: 24 May 2013 / Accepted: 26 May 2013
!Springer-Verlag Berlin Heidelberg 2013
Abstract Vagrant southern elephant seals (Mirounga
leonina) are occasionally sighted along the coast of South
Africa and are known to feed primarily on fish and squid.
Phocid seals are not known to predate on mammals making
the events described here exceptional. This note describes
the successful and failed attempts of a vagrant male
southern elephant seal (M. leonina) to consume Cape fur
seal (Arctocephalus pusillus pusillus) pups in Plettenberg
Bay, South Africa. Observations were made by crew and
passengers aboard a commercial whale-watching vessel
during November 2012. This is the first account of elephant
seals eating anything other than fish, squid and penguins
and suggests considerable plasticity in prey choice dictated
by environmental conditions.
Keywords Southern elephant seal !Mirounga leonina !
Cape fur seal !Arctocephalus pusillus pusillus !Predation
Introduction
Southern elephant seals (Mirounga leonina) have a cir-
cumpolar distribution and typically haul out on Antarctic
and sub-Antarctic islands (Laws 1994). Sightings of
vagrant elephant seals have been reported from the coast of
South Africa, approximately 2,000 km from the nearest
breeding colonies on the Prince Edward Islands (Bester
1989) and over 4,825 km from South Georgia, the source
of a tagged yearling (Vaughan 1967). Temperate conti-
nental latitudes are within the outer fringes of normal
dispersal, and elephant seals sighted along the South
African coast could have originated from any of the
Southern Ocean breeding locations (Oosthuizen et al.
1988).
Records of southern elephant seals from the southern
African coastline are not uncommon, and sightings usually
occur from November to February (Oosthuizen et al. 1988;
Mertz and Bester 2011) during the moulting season of
primarily immatures/subadults of both sexes and of adult
females (Kirkman et al. 2003).
In Plettenberg Bay, there have been several undocu-
mented sightings of southern elephant seals on or near the
Cape fur seal colony at the Robberg Nature Reserve
(S34"060, E23"220). These verbal reports come from Cape
Nature Conservation rangers and the commercial whale-
watching and seal diving operators in the area and are no
longer unusual, perhaps as a result of the recolonization of
the Robberg Peninsula by Cape fur seals from the early
1990s (Huisamen et al. 2011) with a concomitant increase
in tourism and nature conservation activities on the
peninsula.
Description of events
What is unusual were the events witnessed on November
18, 2012, from the commercial whale-watching vessel
Fatboy of the company Ocean Safaris. Whilst observing
the fur seal colony on their last tour of the day, the crew
G. S. Penry (&)!M. N. Bester
Department of Zoology and Entomology, Mammal Research
Institute, University of Pretoria, Private Bag X20, Hatfield,
Pretoria 0028, South Africa
e-mail: gpenry@iziko.org.za
A. C. Baartman
Ocean Safaris, PO Box 2194, Plettenberg Bay, Western Cape
6600, South Africa
123
Polar Biol
DOI 10.1007/s00300-013-1350-4

reported a high number of new born fur seal pups on the
rocks. At 14:54, they observed a male elephant seal
(Fig. 1a) in the water adjacent to the colony, with a fur seal
pup in its mouth (Fig. 1b–d). The fur seal pup was still
alive and the elephant seal proceeded to repeatedly thrash
the pup on the surface of the water for approximately
4 min in the same manner described for an elephant seal
consuming a large fish elsewhere (Reid and Nevitt 1998).
Small pieces of the pup could be seen scattered around the
elephant seal (B. van Uum, pers. obs). The elephant seal
then tilted its head back (Fig. 1d) and swallowed the pup
whole with no apparent difficulty. While this occurred, the
other fur seals in close proximity to the elephant seal were
seemingly unperturbed. The elephant seal was observed in
the area for approximately 2 months and is believed to be
the same individual seen at the Robberg colony 1 year
earlier (November 2011) although there were no photo-
graphs taken to confirm individual identification. During
the 2011 encounter, the elephant seal was observed with a
live fur seal pup in its mouth; however, the pup managed
to escape onto the rocks and was not consumed (A. Ba-
artman, pers. obs). In November 2010, an elephant seal
was seen chewing on an unconfirmed species of sessile
ascidian (sea squirt), whilst on the rocks at the Robberg fur
seal colony.
Discussion
These observations of predation constitute exceptional
behaviour as the opportunistic, generalist feeding southern
elephant seals take predominantly squid and fish
(Rodhouse et al. 1992; Pauly et al. 1998; Daneri et al.
2000; van den Hoff et al. 2003). They have never been
reported to consume mammals, although during September
through November 1997–1999, a male southern elephant
seal killed at least 88 breeding Magellanic penguins
(Spheniscus magellanicus) on land at the Punta Tombo
Provincial Reserve in Chubut, Argentina; not all the pen-
guins killed were eaten and food was likely not the primary
motivating factor for this behaviour (Clark and Boersma
2006). Except for leopard seals, Hydrurga leptonyx, phocid
seals do not predate on marine mammals (e.g. Pauly et al.
1998; Southwell et al. 2012) although otariids such as male
Steller (Eumetopias jubatus), New Zealand (Phocarctos
hookeri) and South American (Otaria byronia) sea lions
kill and eat fur seal pups (Harcourt 1993; Reeves et al.
2002) and Stellers’ consume even other phocids (Mathews
and Adkison 2010) as do Pacific walruses (Lowry and Fay
1984).
Although it is not possible to confirm whether the
individual in question was also sighted in 2011, identifiable
Fig. 1 Male elephant seal (M. leonina) at the Cape fur seal colony,
Robberg Peninsula, Plettenberg Bay: abottling close inshore to the
colony, bshowing the pronounced proboscis, characteristic of male
elephant seals, as it swims towards the boat with the fur seal pup in its
jaws, cother young fur seals play nearby as the elephant seal thrashes
the pup around, dbefore swallowing it (photos B. J. L. van Uum)
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123

individuals do on occasion return to the same areas as
vagrants over consecutive years. An adult male southern
elephant seal returned to the Van Reenen Bay Cape fur seal
colony in Namibia over seven breeding seasons between
1977 and 1983 (Oosthuizen et al. 1988) and another male,
first sighted at Kangaroo Island, South Australia, was
repeatedly sighted over several years usually within a
breeding colony of New Zealand fur seals, A. forsteri
(Shaughnessy et al. 2012).
Cape fur seals appear to tolerate the presence of ele-
phant seals at their rookeries; however, a male elephant
seal at Van Reenen Bay killed several female fur seals
whilst attempting to copulate with them (Best et al. 1981).
This individual grabbed the fur seal pups in what appeared
to be an attempt to lure the females towards it; however, no
pups were seen to be deliberately killed or eaten.
We can only speculate that the southern elephant seals
sighted at Robberg, outside of their usual foraging range,
perhaps needed to be extremely opportunistic in order to
find enough prey. Being sufficiently hungry, it could be
that fresh, perhaps moribund fur seal pups presented easy
pickings, and even sessile invertebrate ascidians became
attractive (present study). We conclude that southern ele-
phant seals are frequent visitors to South African shores,
some conceivably returning repeatedly, and upon occasion
take Cape fur seal pups to supplement their usual cepha-
lopod and fish diet.
Acknowledgments We thank Ben van Uum for permission to use
his photographs in this note, Ocean Safaris whale-watching company
for reporting the event, and Marlon Baartman (head skipper at Ocean
Safaris) for providing additional information on previous sightings of
elephant seals in Plettenberg Bay.
Conflict of interest None.
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