Antarctic Science 10 (1): 75-81 (1998)
Seasonal occurrence and diet of leopard seals (Hydrurga
leptonyx) at Bird Island, South Georgia
T.R. WALKER, I.L. BOYD*, D.J. McCAFFERTY, N. HUN, R.I. TAYLOR and K. REID
British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, UK
Abstract: Seasonal haul-out patterns and diet of individually marked leopard seals (Hydrurga leptonyx) were
investigated at Bird Island, South Georgia during the 1983-96 winters. A total of 2956 leopard seal sightings
weremade, and 121 seals were tagged during the study, mainly between 1993 and 1996. Photographs of scars
and pelage patterns were also used to identify a subset of these individuals across years, which provided no
evidence of tag loss between or within years. Leopard seals were observed between April and November; the
mean time between the first and last sightings in each year was 208 d (s d & 48). Between 1993-96, eight seals
were resident around the island for more than 100 d, and the longest recorded residence was 130 d. The
proportion of tagged seals resighted was 0.35 and 0.17 in 1995 and 1996 respectively. Based on estimates
of body length, 4%
of the seals were juveniles (0-1 years) and ~ 7 0 %
considerable inter-annual variation in abundance, with a maximum of 502 sightings during 1994, compared
with a minimum of 21 during 1986 and 1989. Antarctic fur seals (Arctocephalus gazella) were the main prey
item (58% of kills observed and 53% of scats). Other items included penguins (28% of kills observed and 20%
of scats) and fish (24% of scats). Antarctic krill (Euphausia superba), southern elephant seals (Mirounga
leonina) and seabirds other than penguins were also present in the diet in small quantities.
were not sexually mature. There was
Received 24 April 1997, accepted 27 October 1997
Key words: abundance, diet, fur seal, leopard seal, penguin, predation, seasonality, South Georgia
The leopard seal (Hydrurga leptonyx de Blainville) is one of
themost widespread of the Antarctic seals and has areputation
as a powerful, and potentially significant predator of seabirds
and other seals. Despite this, little is known about its general
ecology. The leopard seal has a circumpolar distribution
occuring primarily throughout Antarctic pack ice during the
breeding season, from November to late December (Laws
1984, Siniff & Stone 1985). There appears to be a seasonal
dispersal northwards to subantarctic islands during the winter
(Gwynn 1953, Rounsevell & Eberhard 1980, Borsa 1990),
although small numbers have been observed throughout the
year at Iles Kerguelen (Bester 198 1, Bester & Roux 1986) and
Heard Island (Gwynn 1953, Brown 1957).
The diet of the leopard seal in the pack ice is reported to
consist of diverse prey items which most commonly include
other seals, such as crabeater seals (Gilbert & Erikson 1977,
Oritsland 1977, Siniff et al. 1979), fish (Green & Williams
1986), cephalopods (Siniff & Stone 1985) and krill (Lowry
et al. 1988). The predatory behaviour of leopard seals at
penguin colonies has been well documented (Penney &
Lowry 1967, Hunt 1973, Muller-Schwarze & Muller-
Schwarze 1975, Siniff & Stone 1985, Bester & Roux 1986,
Borsa 1990, Kooyman et al. 1990, Rogers & Bryden 1995)
but little is known of the diet and hunting techniques in other
areas, although there is evidence for spatial and temporal
variation in the relative proportions of the various prey items
South Georgia (54"59S, 36'25'W) lies 200-300 km south
of the Antarctic Polar Front but usually remains free of pack
ice during winter. Leopard seals were first observed during
the southern winter at South Georgia during the height of the
whalingindustry (Matthews 1929). Since 1983, observations
have been made of leopard seals by the staff of the British
Antarctic Survey station at Bird Island (54"00'S, 38'02'W).
Intensive tagging was initiated at Bird Island during
winter 1993 and continued throughout the 1994, 1995 and
1996 winters. This study was established to help interpret
interannual variability in the number of leopard seals observed
at Bird Island and it addressed three main questions;
1) do leopard seals return to forage at the same sites in
2) what is the rate of turnover of individuals in the
3) what is the main prey of these leopard seals?
Seasonal haulout and interannual variability
Leopard seals were counted daily on beaches within the
region of Bird Island known as Jordan Cove (Landing Beach,
Freshwater Beach and Main Bay) from April through to
T.R. WALKER et a/.
November during the 1994-96 winters. These beach sites
have been described previously (Boyd 1989). Approximately
once per week leopard seals were counted on the remaining
beaches of the island (Everman Cove and Johnson Beach).
Total numbers of leopard seal sightings for Freshwater
Beach were also available each year from 1983-93. Probable
inter-annual variation in observer effort was reduced by
using only those sightings made at Freshwater Beach, the
location of the research station. A standard system of
recording all leopard seal sightings was used: any leopard
seal that was on land or feeding at Freshwater Beach was
recorded with the date of observation, the detailed location on
the beach and the name of the observer. Records were made
on a daily basis to eliminate multiple records for an individual
seal on the same day. Once leopard seals move on to land they
tend to remain in a single location for periods of hours and
they do not tend to return to land again on the same day once
they have re-entered the water.
Before 1993 photographs were the only method used to
help identify individual seals across years. Tagging (Dalton
Jumbotags, Dalton Supplies Ltd., UK) took place during
1993-96. Each tag was stamped with an identifying number
and the message, ‘Inform British Antarctic Survey’. All
seals were tagged in the interdigital membrane of the hind
flippers. Where possible individual seals were double tagged
(one tag in each of the hind flippers). Double tagging was
only possible when an individual was found asleep a second
time. In addition, and where possible, leopard seals on
beaches were also photographed for identification by pelage
patterns and scars. This was to help calculate any possible tag
loss rates within and across years. Total straight line length
was measured (from nose to tip of hind flipper) in those seals
that were asleep in an appropriate posture (i.e. stretched out
straight). Standard length (nose to tail) was derived by
multiplying this total body length by 0.89 (Laws 1957).
Those seals that could not be tagged when first sighted were
marked with gloss paint. Paint marks remained visible for at
least one month after application, allowing seals to be
identified later if subsequently tagged. Incidental resights of
painted and tagged individuals were made in addition to
those during the daily count.
A single leopard seal was tagged (“Allflex” medium sheep
tags, Delta Plastics Ltd., New Zealand) in 1988. Others (n =
14) were photographed between 1984 and 1993.
Diet and predation
During the 1994 and 1995 winters, scats were collected from
known individual seals that had been seen defaecating. Scats
were analysed as described by Reid (1995). Leopard seals
preying on seabirds and mammals were observed
opportunistically during daily rounds of the study area and
activities around the research station.
Of five leopard seals double tagged during winter 1994, two
were re-sighted during the 1995 winter season and both had
retained both their tags. In addition, 12 taggedseals identified.
using distinguishing scars and pelage patterns, from
photographs taken in 1994 and matched in a blind trial
including all photographs of seals taken in 1995, had also
retained their tags. This information suggests that tag loss
was low enough to be insignificant in this study.
Seasonul haulout and interannual variability in numbers
A total of 2956 leopard seal sightings was made at Freshwater
Beach between April 1983 and November 1996 (Table I).
One hundred and forty-six seals were tagged. Individuals
were observed when lying on beaches, ice floes and icebergs
or when in the water, swimming, sleeping or hunting. The
ease with which it was possible to read tag numbers depended
on the location of the observation but, in general, only when
animals were asleep on the beaches could the numbers be
read reliably. Many individuals were observed sleeping in
the middle of kelp beds with their heads clear of the water.
Other sightings included groups of 2-3, but occasionally up
to 7 leopard seals, apparently involved in copulations. Winter
sightings usually began in April, peaked in August, declined
through October and ended in November (Table I). Early
sightings in January and February usually occurred at the
large macaroni penguin colonies around the island. The
mean duration of the season of presence of leopard seals at
Bird Island was 208 d (s d k 48). The index of abundance,
based on the total number of leopard seal days per month at
Freshwater Beach, between 1983 and 1996 showed a high
Table I. Frequency ofoccurrcnce (expressed as the total number of
leopard seal days recorded) and duration (time from first to last sighting
each year) of leopard seals at Bird Island, South Georgia, 1982-96.
Year Frequency Duration
Meanksd 211 k 184
208 * 48
18 Am k 39d
1 I Nov
16 Nov c 17d
DIET OF LEOPARD SEALS, SOUTH GEORGIA
Fig. 1. Numbers of leopard seals
observed at Freshwater Beach, Bird
Island, South Georgia. Observations
are expressed as the total number of
leopard seal days each month
I I I
I I I
1983 1984 1985 1986 19871988 1989 1990 1991 1992 1993 19941995 1996
degree of seasonal and inter-annual variation in the absolute
numbers of seals sighted (Fig. 1). However, there was a
significant trend showing an apparent increase in the numbers
of seals sighted through the period of observation (ANOVA,
F,,,, = 7.77, P < 0.02).
The pattern of presence and absence of tagged leopard seals
in the study area over three seasons from 1994-96 (Fig. 2)
shows that they arrived throughout the period from May
through September and that many of those arriving early
were present at Bird Island into late September and October.
However, there were differences between years. In 1994,
arrivals appeared to be later than in the subsequent years and
in 1996 few of the seals that arrived early were observed after
July. Also in 1996, few new seals were observed during July
and August but there was an increase in new arrivals during
September and October.
Of the 153 leopard seals tagged or photographed, 129 were
tagged and 24 were identified only from photographs.
Photographs were only used as the sole form of identification
for leopard seals seen before 1993. Forty four were not seen
again at Bird Island after the first recorded day of residence
and a further 27 were seen only once after tagging. Thirty
four seals stayed at the island for more than 50 d, and eight
stayed for more than 100 d (Table 11). The longest recorded
residence was 150 d. This seal was resighted six times
between 21 May and its last sighting on 28 September 1996,
and it was also present in three consecutive years.
Tag resighting between years
Fourteen leopard seals were resighted in years subsequent to
tagging. One seal with a white Allflex tag, which had been
deployed in 1988, was resighted once in 1990 and four times
in 1996. Eight seals were present through three consecutive
seasons. These seals were often seen ashore on the same
beach sites at which they were tagged (Fig. 3). Not only was
there a tendency for seals to be observed on the same beaches,
but the same specific locations upon those beaches also
tended to be used.
Only four tags were applied in 1993 and one of these
individuals was resighted in 1994. Of the 42 individuals
tagged during 1994, 11 were seen at Bird Island in 1995,
which represents a 26% recovery rate. Eight of these
individuals were then resighted again in 1996 when another
individual that had been tagged in 1994 but not seen in 1995
was also resighted. Of 3 1 seals tagged in 1995, only one was
resighted in 1996. A further 53 tags were applied in 1996.
These data show that most resightings were of seals tagged
in 1994. This is probably because a small group of individuals,
representing about one-third to one-fifth of the population in
any one year, may be considered to be resident animals in the
sense that they tend to return to the same locations in
Table 11. Durations of residence for individual leopard seals either known
from photographs or tagged at Bird Island, South Georgia, 1984-96.
Number of leopard seals
1984 1985 1987 1988 1993 1994 1995 1996 Total
3 4 44 31
T.R. WALKER eta/.
Fig. 2. Patterns of presence and absence of leopard seals tagged at Bird Island, South Georgia during 1994-96. Each row represents
an individual leopard seal; blanked off regions show the period when the leopard seal was observed ashore.
One tagged individual was resighted at Seal Island, South
Shetland Islands (6Oo59'S 55"23'W) on 18 Jan 1995 (Lisa
Hiruki, personal communication). This animal had been
tagged on 7 October 1994 and had therefore taken
approximately three months to cover a minimum distance of
1300 km from Bird Island. This individual was only ever
seen on the day of tagging at Bird Island.
Age and sex classes observed
Leopard seals measured during the study, were allocated,
based on their lengths, to the age and sex classes shown in
Table 111. Seals of adult size (>4 years) accounted for
20-25% ofthe population with the remainderbeing immatures
although less than 5% were classified as <1 year old. Males
Key to locations
1 Main Bay
2 Freshwater Beach
3 Landing Beach
Fig. 3. Locations of six leopard seals originally
tagged at Freshwater Beach, Bird Island,
South Georgia, obtained from observations
between 10.00-1 2.00 and 18.00-20.00 daily.
Seals tended to come ashore at specific
locations upon the same beaches. All beaches
were within a 3 km stretch of coastline.
DIET OF LEOPARD SEALS, SOUTH GEORGIA
y- 60 -
Table 111. Age and sex composition of leopard seals at Bird Island, South
Georgia. Ages were estimated from standard length using the method
described by Laws (1957). Results are given for all marked seals where
Estimate age (years)
n Males Females
1-2 2-3 3-4 >4
26.0 19.3 32.3
were present in greater numbers each year than females
(Table 111) and they also arrived earlier in the winter than
females (Fig. 4). Ten individuals measured in successive
years (1994 and 1995) showed no significant increase in
length between years (one way ANOVA F,,9 = 0.22 P >0.6).
Overall, leopard seals appeared to be in good condition and
one individual (mass 155 kg), which died of an unknown
cause, had a sternal blubber depth of 4.5 cm and a total
blubber content of 35% of body mass based on the formula
of Ryg et al. (1990).
Diet and predation
Direct observation of predation by leopard seals at Bird
Island showed that kills invariably occured in the water and
Antarctic fur seals accounted for most of the observed kills
(Table IV). Gentoo penguins were the next most commonly
observed item in the leopard seal diet during the winter
months and macaroni penguins were eaten by leopard seals
during the summer.
The prey components contained in scats collected from
leopard seals at Bird Island (n = 45) showed that more than
half (53.3%) contained the remains of juvenile Antarctic fur
seals (Table V). The proportions of fish and penguin prey
remains in the scats were similar, comprizing only one
quarter and one fifth of all scats sorted, respectively. Only
one scat contained krill, but this was after large quantities
were seen washed up on the beaches around Bird Island. Five
scats were collected from one female leopard seal and all of
these contained only fur seal hair.
Table V. Frequency of occurrence of prey items from scats (n = 45) of
tagged leopard seals during 1994 and 1995.
Year Prey items
24 (53) 9 (20)
Table IV. Number and proponion of prey items (n = 162) taken by
leopard seals at Bird Island, South Georgia, 1983-95.
Antarctic fur seal (sub-adult) (Arctocephalus gazella) 94
Elephant seal (Miroungu leonina)*
Gentoo penguin (Pygoscelis pupuu)
Macaroni penguin (Eudyptes chrysolophus)
Diving petrel (Pelecanoides sp.)
Cape petrel (Duption cupense)
* all observations were of small (c. 1.5-2.0 m) elephant seals,
As at other subantarctic sites (Rounsevell & Eberhard 1980,
Borsa 1990), there was a seasonal pattern of abundance with
sightings throughout the winter, usually peaking in August
or September, and animals generally being absent from late
spring to mid-autumn. While this pattern was consistent
between years, there was large inter-annual variation in the
numbers of seals sighted. The measure of leopard seal
abundance did not take into account multiple sightings of the
same individual on different days so it could have been
influenced by small numbers of individuals taking up residence
at Bird Island. Therefore the total number of leopard seal
days observed in each month (Fig. 1) will not provide a true
representation of variations in the total numbers of leopard
seals present at Bird Island. Similar interannual variability
has been observed at Macquarie Island and a 4-5 year
periodicity has been suggested (Rounsevell 1988, Testa
et al. 1991). Temporal overlap between the Macquarie
Island and Bird Island data sets is insufficient to examine the
possibility that changes at these sites are in phase but the
Apr May Jun Jul Aug Sep Oct
Fig. 4. Percentages of male and female leopard seals arriving
at Bird Island, South Georgia, by month, between 1994-96.
T.R. WALKER etal.
periodicity of change at Bird Island appears to be 3 4 years,
based on the two complete cycles observed to date.
There was an apparent increase in the abundance of
leopard seals at Bird Island since 1983. Although efforts
were made both in the field and during analysis to standardize
the observer effort across the whole of the study period, it
remains possible that this increase was caused by increased
observer effort as the study progressed. However, it is also
possible that it may signal an increasing population in the
region, possibly attracted by increasingly abundant fur seal
prey (Boyd 1993).
Based on measurements of body length most of the leopard
seals hauling out at Bird Island were immature. One-third to
one-fifth of seals returned in successive years and the
observation that these individuals did not show any significant
increment in length between years suggests that they were
mainly adult seals. The high frequency of immatures also
concurs with the observations of leopard seals at Macquarie
Island (Rounsevell 1988) but this is the first example of long-
term site fidelity in leopard seals. It appears that the winter
leopard seal population at Bird Island is composed of a small
group (10-15) of individuals that return annually, another
larger group that may remain within the region for a period
of 1-3 months within a season and a still larger group that
appears to be present for periods of <10 days and that were
never seen again (Table 11). In addition, those seals that were
resident at Bird Island tended to use specific locations for
Foraging behaviour, diet and movements
The observations of diet and predation are likely to have been
biased towards those individuals that were resident at Bird
Island and they suggest strongly that these animals were
attracted to this location because of the availability of seals
and penguins throughout the winter. Past observations at
South Georgia, Iles Kerguelen and Heard Island have also
suggested the importance of Antarctic fur seals in the diet of
leopard seals (McCann & Doidge 1987, Borsa 1990,
Shaughnessy etal. 1998). However, the diet observed in this
study may not reflect the diet of leopard seals in general. It
is possible that the current observations are of a small group
of leopard seals which exploit a specialist niche. This is
supported by the presence of one leopard seal, that had been
tagged at Bird Island, at a fur seal colony in the region of the
Antarctic Peninsula. Past observations of leopard seal diets
suggest that the principal components are fish (Green &
Williams 1986) and krill (Lowry et al. 1988).
The relatively small number of juvenile (0-1 year old)
leopard seals observed at Bird Island suggests that these
individuals do not tend to exploit large vertebrate prey like
seals and penguins (see also Siniff & Bengtson 1977). Young
leopard seals may not have sufficient ability to exploit such
a prey resource or they may bc excluded from such prey by
competition with adult leopard seals for the most profitable
feeding locations. However, there was insufficient data
matching observations of predation on prey of different sizes
and the sex or age class of leopard seals in this study to allow
comparison of diets between different classes of individuals.
Gilbert & Erickson (1977) suggested that northward
dispersal of non-breeding individuals may occur in winter
due to intraspecific competition for food or because of limited
access to food in the winter sea ice. Furthermore, based on
surveys of leopard seals in pack ice, Rogers & Bryden (1997)
suggested that competition for space could influence the
dispersion. The results of this study showing that specific
individuals tend to occupy specific areas support the view
that leopard seals may compete for access to prime habitat,
such as around fur seal and penguin colonies (Bester & Roux
1986, Borsa 1990).
The sex ratio was biased in favour of males during the early
part of the winter. This suggests that males may move north
out of the pack icc before females. The general bias in sex
ratio could represent a bias within the population as a whole
but it is more likely to reflect different diet selectivity by the
sexes and suggests that males may be more likely to take large
vertebrate prey. The movement of seals away from Bird
IslandinOctober coincides with the beginning oftherecession
of the pack ice and the assumed breeding season for leopard
seals (Siniff & Stone 1985). Therefore, seals may move south
in October to breed and because they will then have access to
additional feeding areas as the sea ice begins to break up and
recede. Only one record, from September 1987, exists of a
leopard seal birth at Bird Island, while none has been
reported at Macquarie Island (Rounsevell & Eberhard 1980).
This study has confirmed that leopard seals take a wide
varicty of prey, including young elephant seals (see also
Gwynn 1953, Siniff& Bengtson 1977, Borsa 1990). The fish
remains observed in leopard seal scats collected at Bird
Island must be interpreted with caution as these remains may
have derived from the gut of mammalian or avian prey since
fish are known to be important in the winter diet of Antarctic
fur seals (Reid 1995) and gentoo penguins (Williams 1991).
These results have shown that the abundance of leopard seals
at Bird Island varies seasonally and between years, possibly
in a 3-4 year cycle. Small numbers of individual animals
show fidelity with and between years to specific locations for
hauling out and also probably for feeding. These individuals
appear to feed mainly on seals and penguins, at least through
the winter period. Leopard seal numbers at Bird Island may
have increased since the study began in 1983.
DIET OF LEOPARD SEALS, SOUTH GEORGIA Download full-text
We especially thank all the past overwintering staff at the
British Antarctic Survey base on Bird Island for recording
leopard seal sightings. In particular, we thank Dr N. Cobley,
Richard Humpidge and Dr S. Berrow for spending countless
hours in the field helping with tagging and resights and for
constructive comments on the manuscript. We thank
Dr P.L. Boveng, Lisa Hiruki and the other US researchers on
Seal Island, Antarctica for passing on details of a resighting
during 1995. We are grateful to Dr M.N. Bester,
Dr P.L. Boveng and Dr P.D. Shaughnessy for commenting on
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