Abstract

One leucistic and one partially leucistic Antarctic fur seal Arctocephalus gazella were seen at Bouvetya during the 1996/97 austral summer. Both likely came from South Georgia, where this colour morph is common. No individuals of this colour morph were sighted during three subsequent expeditions to Bouvetya. The prevalence of this colour morph in the abundant populations of the Scotia Arc may be due to founder effect, as at least one leucistic animal was present at South Georgia when the Antarctic fur seal was close to extinction.
SHORT NOTE
G. J. Greg Hofmeyr ÆMartha
´n N. Bester
Steve P. Kirkman
Leucistic Antarctic fur seals at Bouvetøya
Received: 16 February 2005 / Revised: 3 June 2005 / Accepted: 12 June 2005 / Published online: 2 August 2005
Springer-Verlag 2005
Abstract One leucistic and one partially leucistic Ant-
arctic fur seal Arctocephalus gazella were seen at Bou-
vetøya during the 1996/97 austral summer. Both likely
came from South Georgia, where this colour morph is
common. No individuals of this colour morph were
sighted during three subsequent expeditions to Bou-
vetøya. The prevalence of this colour morph in the
abundant populations of the Scotia Arc may be due to
founder effect, as at least one leucistic animal was
present at South Georgia when the Antarctic fur seal
was close to extinction.
Keywords Arctocephalus gazella ÆLeucism Æ
Bouvetøya ÆFounder effect
Introduction
Antarctic fur seals Arctocephalus gazella were severely
reduced during the nineteenth and early twentieth cen-
turies by uncontrolled hunting, with most populations
becoming extinct (Bonner 1968). The species has since
experienced a strong recovery, recolonising many of its
former breeding sites. The global population now ex-
ceeds 2,700,000 individuals at 10 islands or island groups
(Boyd 1993; Hofmeyr et al. 2005). Leucistic Antarctic
fur seals have been observed regularly at two sites, South
Georgia (Bonner 1968) and the South Shetland Islands
(Aguayo 1978; Aguayo and Torres 1967 in Cardenas
and Yan
˜ez 1983; Cardenas and Yan
˜ez 1983). The only
other sites where this colour morph has been recorded
are two other island groups within the Scotia Arc, the
South Sandwich Islands (Baker et al. 1964) and the
South Orkney Islands (Øritsland 1960 in Bonner 1968).
Budd (1972) did record a light coloured adult male of
this species at Heard Island, but it is apparent from both
the comments and the photo in the publication that the
seal in question was not leucistic.
Bouvetøya (5425¢S, 320¢E), a subantarctic island,
supports the second largest population of Antarctic fur
seals globally, with a pup production of some 15,000
recorded for the coastal platform Nyrøysa (Hofmeyr
et al. 2005). Relatively few pups are born elsewhere on
the island. During a series of four expeditions in the
austral summers of 1996/1997, 1998/1999, 2000/2001
and 2001/2002, data was collected at this rookery as part
of the Commission for the Conservation of Antarctic
Marine Living Resources (CCAMLR) Ecosystem
Monitoring Programme. All unusual animals and their
behaviour seen during the expeditions were noted.
Methods
Daily field work allowed observers to visit and observe
most of the rookery over a period of approximately
3 months during each expedition. All parts were visited
or observed at least weekly. During the first expedition
one leucistic and one partially leucistic animal were re-
corded. Both were quietly approached within 5 m,
photographed and their appearance and behaviour no-
ted.
Results
The leucistic animal (Fig. 1), a yearling of unknown sex,
was seen from 28–31st January 1997. The partially leu-
cistic animal (Fig. 2) was an adult female that was seen
several times from mid-December 1996 to mid-February
1997, while suckling an apparently healthy pup of nor-
mal colouration. In both individuals, the vibrissae of the
muzzle and eyebrows were white, and most of the pelage
was creamy white in colour. The fur on the flippers was a
light tan darkening towards the border with the skin,
while that on the ears and around the eyes, nose and
mouth was a very pale tan. All exposed skin (flippers,
G. J. G. Hofmeyr (&)ÆM. N. Bester ÆS. P. Kirkman
Mammal Research Institute, Department of Zoology Entomology,
University of Pretoria, Pretoria, 0002 South Africa
E-mail: ghofmeyr@zoology.up.ac.za
Polar Biol (2005) 29: 77–79
DOI 10.1007/s00300-005-0030-4
ears and nose), and the eyes, were the normal dark
brown of this species. The adult female differed from the
yearling in that many of the guard hairs on her shoul-
ders, upper back, the back of her neck, her flanks and
rump and on parts of her face were grey. Although both
animals appeared to be healthy, neither was resighted on
any of the three subsequent expeditions.
Discussion
Incidences of leucistic pups amongst their normally
coloured conspecifics at South Georgia have been re-
ported at 1 in 1,500 (Bonner 1958), 1 in 400 to 1 in 800
(Bonner 1968) and 1 in 1,000 (Bonner 1964; Laws 1993).
During a count of 3,427 individuals of all ages and both
sexes at a number of islands of the South Shetlands,
Aguayo (1978) recorded two leucistic animals (1 in
1,713), while Cardenas and Yan
˜ez (1983) reported three
juveniles amongst 412 (also reported as 413), or a ratio
of 1 in 138. These ratios are considerably higher than for
a number of other species of animals (Jehl 1985; Owen
and Shimmings 1992; Forrest and Naveen 2000). They
are, however, similar to the frequencies at which
abnormal colour morphs were found in certain popu-
lations of feral birds (Reese 1980; Randler 1994). Unu-
sual colour morphs are often selected captive animals
and it is therefore to be expected that a high proportion
of animals with these colour patterns will be encoun-
tered in populations founded by escapees.
It is quite possible that the presence of such a large
number of leucistic individuals in the Antarctic fur seal
population of South Georgia is also due to founder ef-
fect. Bonner (1958) suggested that the high levels of
leucism at South Georgia were ‘not so surprising in a
population ... which is rapidly increasing after reduction
to a very low level’. At least one leucistic animal was
observed amongst the South Georgia population in 1933
(Bonner 1968). Cardenas and Yan
˜ez (1983) suggested
that the presence of this individual amongst the 60
counted in 1933 (Rayner 1933 in Bonner 1968), shortly
after the population had reached its nadir and prior to
its rapid increase, was possibly responsible for leucism
being relatively prevalent amongst the population of
South Georgia, and the populations of other islands of
the Scotia Arc. The latter populations are derived from
the South Georgia population (Wynen et al. 2000).
Leucistic pups were not noted on Bouvetøya amongst
the approximately 50,000 present during the course of
the last four expeditions to the island. Leucistic animals
are conspicuous and it is extremely unlikely that any
would have been missed. It is quite possible that the
leucistic animals sighted at Bouvetøya originated at
South Georgia. The Bouvetøya population increased at
a mean annual rate of over 30% between 1990 and 1996
(Hofmeyr et al. 2005). This rate was probably sustain-
Fig. 1 Photograph of a leucistic
yearling Antarctic fur seal at
Nyrøysa, Bouvetøya. Photo:
G.J.G. Hofmeyr
Fig. 2 Photograph of a partially leucistic adult female Antarctic fur
seal at Nyrøysa, Bouvetøya. Photo: G.J.G. Hofmeyr
78
able only by immigration from the very large population
at South Georgia, which site is responsible for 90% of
global pup production of this species (Boyd 1993; Hof-
meyr et al. 2005). Wynen et al. (2000) showed that while
a number of haplotypes were unique to the Bouvetøya
population, there was also considerable genetic similar-
ity between the South Georgia and Bouvetøya popula-
tions. It is quite likely that this is due to immigration.
Records of vagrant Antarctic fur seals (Payne 1979;
Shaughnessy and Burton 1986) show that individuals of
this species are capable of moving far from their natal
population.
Acknowledgements These observations were recorded during a
study financed by the Norwegian Polar Institute and NORAD.
Further support was provided by the Mammal Research Institute
of the University of Pretoria. We thank Kit Kovacs, Christian
Lydersen and Ian Gjertz for their contributions to the fur seal work
at Bouvetøya. We are also grateful to Daniel Torres N., Roger
Kirkwood and one anonymous reviewer for their comments.
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Compiled by the Group of Specialists on Seals of the Scientific Committee on Antarctic Research, this book gives a detailed account of the various methodologies, techniques, procedures and rationale for the collection and initial analysis of data on the biology and population ecology of Antarctic seals. The individually authored chapters cover the techniques invloved in species identification and age determination, and those used in the study of behaviour, population ecology, morphometrics, genetics, pollutant accumulation, reproduction, diet and bioenergetics. Capture, tagging, immobilization and kiling methods are dealt with. -S.J.Stone
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Leucism is the complete loss of a particular pigment, or all pigments, in feathers but not in soft-parts. It may be as slight as a single white feather or as pervasive as an all-white bird with normal eyes, bill, and legs (Buckley 1982). The condition has been documented, usually as a curiosity and under the term "albinism," in hundreds of species. Its incidence is said to differ greatly among species (e.g., Sage 1963, Gross 1965), but the data for that con-clusion are unconvincing because a high percentage of reports pertain to species that associate with, or are hunted by, man. As a result, observational bias is potentially strong. For only a few species (e.g., storm-petrels; Baptista 1966) has it been possible to consider the phenomenon more broadly and to investigate the frequency of leucism in natural populations of birds. The subject is interesting because leucism, like any variable condition, may provide indirect evidence of underlying genetic variability. Fur-thermore, if its frequency can be measured, this may allow some inferences to be drawn about the strength of selection against abnormally-colored individuals. In this paper, I present data on leucism compiled incidental to other re-search during a four-year (198 l-l 984) study of Eared Grebe (Podiceps nigricollis) biology at Mono Lake, California. Other aspects of this research have been presented else-where (Mahoney and Jehl 1985; Storer and Jehl, in press). Apparently pure white on head, body. Wings pre-sumed to be white, but that is not necessarily the case (Fig. 2). White with gray smudges on head or neck or both. Ear tufts (if present) white or very pale yellow. Wings variable; remiges or coverts or both may be pigmented (Fig. 2). Body white with occasional gray feathers on back or rump (not usually evident except at close range). Wings dark except for (normal) white patch of secondaries. Black or gray markings on crown or nape, often extending around ear tufts onto chin. Ear tufts (if present) golden or pale yellow. Body white. Gray feathers evident on back. Oth-erwise like category 3, except black area on neck is more extensive and occurs on lateral and an-terior surface. Wings as in category 3. Head, neck, and chest black, with golden ear tufts (if present). Back dark, rest of body white. Wings as in category 3. Piebald. Appears uniformly gray at a distance but plumage is a mixture of gray and white feathers. Wing pattern apparently variable. a In cate ories 2A-5A (not listed), the patterns are identical to those in categories 1 -5, but black tones are replaced by brown OT tan.
Article
The purpose of this paper is to report on the present status of the small but growing population of the Antarctic Fur Seal Arctocephalus gazella in the South Shetland Islands (Fig 1). The previous history of the sealing of this species is well documented by O'Gorman (1961, 1963), Bonner and Laws (1964) and Bonner (1964,1968). The current status of this and other species of fur seals, and the species of sea lions and true seals in the Southern Hemisphere, has been summarized by Laws (1973a). Bonner (1968) has made natural history and population studies on Antarctic Fur Seals in South Georgia, and present research here is being carried out by Dr M. R. Payne and two other colleagues of the British Antarctic Survey (Laws, 1973b).
Article
A census of the breeding population of Antarctic fur seals (Arctocephalusgazella) at South Georgia was carried out during the 1990/91 breeding season. Using counts of adult females ashore at the breeding grounds during the pupping period, together with corrections for the likelihood of a female being ashore at a census and for pregnancy rate (71% in 1990/91), pup production was estimated as 269 000 (95% confidence intervals 188 000-350000). The breeding population in 1990/91 was reduced at long-term study sites probably because of limited food availability. Data from these sites were used to estimate the pup production of the population had 1990/91 been a typical year. Based on values from 1983/84 to 1990/91, pup production in 1990/91 would have been 378000 (se=19100) if it had been an average year. The annual increase in pup production from 1976/77 to 1990/91 has declined to 9.8% since the initial period of population expansion in the 1950s and 1960s. Increased population size has led to an expansion of the breeding range at South Georgia.