Leucistic southern elephant seal at Marion Island?

An extraordinary light coloured, young southern elephant seal Mirounga leonina was seen at Marion Island during the 2004 austral spring. This is the second record of an extraordinary white colour morph for the species here. It was not unequivocally established that the animal was leucistic.     

Long distance breeding dispersal of a southern elephant seal

Southern elephant seals range extensively during regular foraging excursions. Despite this they are highly philopatric and long range dispersal is rare. At Gough Island, southern Atlantic Ocean, we observed a breeding adult male elephant seal during September 2009, which had been tagged on its natal beach at Marion Island, southern Indian Ocean, in November 1998. The individual was resighted only once on Marion Island, 6 months after tagging. This 3,860 km movement represents dispersal (and likely gene flow) between distinct populations from different elephant seal geographical provinces. Given the polygynous breeding system of this species, the presence of this single male may have a disproportionate genetic effect on the small number of southern elephant seals breeding at Gough Island.     

Do southern elephant seals show density dependence in fecundity?

Here we provide an alternative interpretation to that of Pistorius et al. (2001), concerning density-dependent increases in fecundity resulting in population regulation of the southern elephant seal population at Marion Island. We do not contradict the findings of Pistorius et al. (2001), because it does appear: (1) that a change in fecundity has been observed, and (2) that some factor related to food supply is the most likely cause for an observed population decline and increase in reproductive performance. The main observation leading to the interpretation of density-dependent feedback in the population of southern elephant seals at Marion Island (one of the Prince Edward Islands) is that there has been a reduction in the population's rate of decline in recent years (reported by Pistorius et al. (1999b)), and that this could have resulted from a per capita increase in food availability. However, because rates of population change are rarely linearly constant, changes in population size should be expressed on a logarithmic, rather than a linear scale, as used by Pistorius et al. (1999b). Re-plotting the linear values of Pistorius et al. (1999b) on the natural logarithmic scale gave no clear change in the rate of population decline; therefore, we conclude that the rate of population change (decline) has remained constant from 1986 to 1997 (r=-0.0439). The Marion Island population is part of the larger Kerguelen population, and there might be considerable overlap in the foraging areas, and possibly prey, exploited by elephant seals from all sub-populations within this larger population. Changes in the number of intra-specific resource competitors at Marion Island are therefore unlikely to alter per capita food availability since the Marion population constitutes approximately 1% of the total Kerguelen population. We propose an alternative hypothesis that the present data support a mechanism driving the proposed increase in per capita food supply through changes in either: (1) inter-specific food competition, (2) rates of predation, (3) changes in weather pattern or (4) disease.     

The role of eddies in the diving behaviour of female southern elephant seals

As the Antarctic Circumpolar Current crosses the South-West Indian Ocean Ridge, it creates an extensive eddy field characterised by high sea level anomaly variability. We investigated the diving behaviour of female southern elephant seals from Marion Island during their post-moult migrations in relation to this eddy field in order to determine its role in the animals’ at-sea dispersal. Most seals dived within the region significantly more often than predicted by chance, and these dives were generally shallower and shorter than dives outside the eddy field. Mixed effects models estimated reductions of 44.33 ± 3.00 m (maximum depth) and 6.37 ± 0.10 min (dive duration) as a result of diving within the region, along with low between-seal variability (maximum depth: 5.5 % and dive duration: 8.4 %). U-shaped dives increased in frequency inside the eddy field, whereas W-shaped dives with multiple vertical movements decreased. Results suggest that Marion Island’s adult female elephant seals’ dives are characterised by lowered cost-of-transport when they encounter the eddy field during the start and end of their post-moult migrations. This might result from changes in buoyancy associated with varying body condition upon leaving and returning to the island. Our results do not suggest that the eddy field is a vital foraging ground for Marion Island’s southern elephant seals. However, because seals preferentially travel through this area and likely forage opportunistically while minimising transport costs, we hypothesise that climate-mediated changes in the nature or position of this region may alter the seals’ at-sea dispersal patterns.     

Leucistic Antarctic fur seal <Emphasis Type="Italic">Arctocephalus gazella</Emphasis> at Marion Island

A leucistic immature male Antarctic fur seal, Arctocephalus gazella, was sighted at Marion Island in April 2006; the first such sighting in three decades of extensive field presence of biologists at this locality. The same animal returned to the island in July/August 2006, when it was moulting, and was marked with unique flipper tags, after which it was sighted in early October 2006 again. Considering that individuals of this species are capable of moving far from their natal population, we suggest that the animal could likely have come from South Georgia, where this colour morph is relatively common.     

Pup mortality in southern elephant seals at Marion Island

Pre- and early post-weaning pup mortality of southern elephant seals (Mirounga leonina) at Marion Island from 1990 through 1999 ranged from 1.6% to 7.3% and averaged 3.8%. Mortality of pups after weaning before their first trip to sea accounted for only 12% of the total mortality. We found no relationship between population size and percentage pup mortality, indicating that pup survival is independent of seal density, at least at the densities of breeding seals that prevailed. Indeed, pup mortality was greatest in the smallest harems, apparently owing to a greater number of younger, less experienced mothers. Small harems were generally also found on less suitable beaches than larger harems and this could have contributed to pup injury as a cause of pup mortality on these beaches. Mother-pup separation and injury caused by beachmasters is likely to be responsible for pup mortality in the larger harems. The low rates of pup mortality observed in this study obviate it being a major population regulating agent at Marion Island.     

Survivorship of a declining population of southern elephant seals, Mirounga leonina, in relation to age, sex and cohort

This study quantified both the age- and sex-specific survival rates of juveniles and adults, and tested for interannual differences in age-specific survival rates of the southern elephant seal population at Marion Island. Pups were tagged on an annual basis from 1983 onwards at Marion Island, and a consistent recapture program yielded data that was analysed using the software package MARK to obtain maximum-likelihood estimates of survival and capture probability. On average, 1st-year survival was 0.58 and 0.62, and survival rate averaged over the first 3 years of life, 0.69 and 0.74 for males and females, respectively. From years 4 to 9, the average survival rate was 0.66 and 0.75 for males and females, respectively. Survival estimates for elephant seals in their 10th–13th year are also presented, although these are based on very small sample sizes. Averages of age-specific survival estimates from the earlier (mostly 1983–1987 cohorts) and later (mostly 1988–1992 cohorts) periods were compared and considerable reductions were observed in 4th- and 5th-year male survival, and 4th-year female survival. The comparatively low adult survival is suggested as the proximate cause, and food limitation as deduced from the decline in survival of elephant seals with comparatively high energetic demands as the ultimate cause behind the population decline at Marion Island. Although not tied in with the decline of the population, 1987, 1990 and 1993 were identified as high-mortality years. Received: 14 December 1998 / Accepted: 14 June 1999     

MOVEMENTS OF SOUTHERN ELEPHANT SEALS AND SUBANTARCTIC FUR SEALS IN RELATION TO MARION ISLAND

Based primarily on an intensive marking/resighting program conducted at Marion Island (46°54'S, 37°45'E) in the Southern Ocean, the inter-island movements of southern elephant seals, Mirounga leonina , and fur seals Arctocephalus spp., were investigated to elucidate their little known pelagic phase. Southern elephant seals, in particular immature animals, readily move between the proximate Marion and Prince Edward islands. Some range as far afield as Iles Crozet, approximately 1,000 km distant where they haul out for the summer molt or during an autumn resting phase. The exchange of individuals between Marion Island and Iles Crozet during the return of immatures for the molt after a winter at sea, suggests overlapping of the foraging ranges of the two populations. Despite their wanderings, the majority of M. leonina from Marion Island probably feed in the proximity of the island, and relocate onto the island for breeding, molting and resting. Of the fur seals, only a few A. tropicalis were seen away from their natal island, in some cases covering distances in excess of 2,000 km. displaying a remarkable dispersal capacity.     

Shifting trends: detecting environmentally mediated regulation in long-lived marine vertebrates using time-series data

Assessing the status and trends in animal populations is essential for effective species conservation and management practices. However, unless time-series abundance data demonstrate rapid and reliable fluctuations, objective appraisal of directionality of trends is problematic. We adopted a multiple-working hypotheses approach based on information-theoretic and Bayesian multi-model inference to examine the population trends and form of intrinsic regulation demonstrated by a long-lived species, the southern elephant seal. We also determined the evidence for density dependence in 11 other well-studied marine mammal species. (1) We tested the type of population regulation for elephant seals from Marion Island (1986–2004) and from 11 other marine mammal species, and (2) we described the trends and behavior of the 19-year population time series at Marion Island to identify changes in population trends. We contrasted five plausible trend models using information-theoretic and Bayesian-inference estimates of model parsimony. Our analyses identified two distinct phases of population growth for this population with the inflexion occurring in 1998. Thus, the population decreased between 1986 and 1997 (−3.7% per annum) and increased between 1997 and 2004 (1.9% per annum). An index of environmental stochasticity, the Southern Oscillation Index, explained some of the variance in r and N. We determined analytically that there was good evidence for density dependence in the Marion Island population and that density dependence was widespread among marine mammal species (67% of species showed evidence for population regulation). This approach demonstrates the potential functionality of a relatively simple technique that can be applied to short time series to identify the type of regulation, and the uncertainty associated with the phenomenon, operating in populations of large mammals.     

BODY TEMPERATURE IN THE NEWBORN SOUTHERN ELEPHANT SEAL, MIROUNGA LEONINA, AT MACQUARIE ISLAND

Newborn southern elephant seal pups were reported by Laws (1953) to be "to some extent poikilothermic at birth." Rectal temperatures of known age southern elephant seal pups were recorded during the 1985 pupping season at Macquarie Island. The mean pup rectal temperature was found to be 381°C ± 0.1°C SEM ( n = 131, range = 36.5°-39.1°C). Pups at two hours, six hours, and one day after birth had significantly higher rectal temperatures than pups two, three, or four days of age. Rectal temperatures of neonatal southern elephant seals were within the range observed for other pinnipeds, (but never as low as the 31°C previously observed for southern elephant seals at Signy Island in 1953). A significant though weak positive correlation was found between pup temperature and body weight. However, no correlation between pup temperature and age or any environmental factor was found. These observations demonstrated that southern elephant seal pups at Macquarie Island are homeothermic, rather than heterothermic from birth.     

Goose barnacles hitchhike on satellite-tracked southern elephant seals

Goose barnacles (Lepas australis) attached to satellite-relay data loggers were carried by three southern elephant seals (Mirounga leonina) from Marion Island. Their movements across the Polar Frontal Zone are presented, providing further evidence that megafauna are potential vectors for the transport of species into the Southern Ocean.     

Population status, trends and a re-examination of the hypotheses explaining the recent declines of the southern elephant seal Mirounga leonina

1. Between the 1950s and 1990s the southern elephant seal Mirounga leonina underwent large decreases in population size throughout most of its breeding range in the Southern Ocean. While current population estimates suggest a recent recovery, some breeding populations have continued to decrease in recent years (Macquarie and Marion Islands), others have either remained stable (South Georgia, Kerguelen and Heard Island) or have increased (Peninsula Valdés, Argentina). 2. Intrinsic hypotheses for patterns of regional decline include factors that are affected by density-dependent mechanisms: (i) paucity of males, (ii) population ‘overshoot’ and (iii) pandemic disease. Extrinsic hypotheses include (iv) predation, (v) competition with fisheries concerns, (vi) interspecific competition, (vii) environmental change and (viii) human disturbance. Of the eight hypotheses proposed and examined here, we conclude that three can be discounted (i, v, viii), three are unlikely, but may require more testing (ii, iii, iv) and two are plausible (vi, vii). 3. The interspecific competition hypothesis is difficult to test because it requires the simultaneous monitoring of species that overlap directly with elephant seals, many of which have not been identified or little is known. However, an analysis of the relationship between log variance and log abundance (Taylor's power law) for populations of southern and northern elephant seals suggests that interspecific competition is not a significant factor in the decline of the southern elephant seal. 4. The hypothesis that decreases in southern elephant seal populations between the 1950s and 1990s were caused by the environmental change is the easiest to test and most plausible of the hypotheses. We propose a framework by which to test this hypothesis to determine how food availability affects individual survival.     

Age-related reproductive variation in a wild marine mammal population

Life history theory predicts a change in reproduction success with age as energy resources are limited and must be allocated effectively to maximize reproduction and survival. In this study, we use three reproductive performance measures, maternal expenditure, offspring weaning mass, and first-year survival, to investigate the role that maternal age plays in successful reproduction. Long-term uninterrupted life history data available for Marion Island’s southern elephant seals and mass change estimates from photogrammetry data allow for assessment of age-related reproduction performance and trade-offs. Known-aged adult females were photographed for photogrammetric mass estimation (n = 29) and their pups weighed at weaning during the 2009 breeding season. Maternal age and proportional mass loss positively influenced pup weaning mass. In turn, first-year pup return rates (as a proxy for survival) were assessed through the intensive mark–recapture program. Pup survival increased with female age and weaning mass. Pups of young females aged 3–6 years have a lower first-year survival probability compared with pups of older and larger females.     

A lifetime at depth: vertical distribution of southern elephant seals in the water column

Although numerous studies have addressed the migration and dive behaviour of southern elephant seals (Mirounga leonina), questions remain about their habitat use in the marine environment. We report on the vertical use of the water column in the species and the potential lifetime implications for southern elephant seals from Marion Island. Long-term mark-resight data were used to complement vertical habitat use for 35 known individuals tagged with satellite-relay data loggers, resulting in cumulative depth use extrapolated for each individual over its estimated lifespan. Seals spent on average 77.59% of their lives diving at sea, 7.06% at the sea surface, and 15.35% hauled out on land. Some segregation was observed in maximum dive depths and depth use between male and female animals—males evidently being physiologically more capable of exploiting increased depths. Females and males spent 86.98 and 80.89% of their lives at sea, respectively. While at sea, all animals spent more time between 300 and 400 m depth, than any other depth category. Males and females spent comparable percentages of their lifetimes below 100 m depth (males: 65.54%; females: 68.92%), though males spent 8.98% of their lives at depths in excess of 700 m, compared to females’ 1.84% at such depths. Adult males often performed benthic dives in excess of 2,000 m, including the deepest known recorded dive of any air-breathing vertebrate (>2,133 m). Our results provide a close approximation of vertical habitat use by southern elephant seals, extrapolated over their lifespans, and we discuss some physiological and developmental implications of their variable depth use.     

Body mass loss of moulting female southern elephant seals,Mirounga leonina,at Macquarie Island

Thirteen female southern elephant seals moulting at Macquarie Island lost an average of 4.46±0.80 kg/day (10.01±1.20g/kg/day). There was no significant difference between this rate of body mass loss and that reported for moulting female southern elephant seals from South Georgia. Moulting female southern elephant seals however exhibited larger mass specific mass loss than either female northern elephant seals or male southern elephant seals, indicating a higher metabolic cost of moult in these animals.     

Mummified and skeletal southern elephant seals (Mirounga leonina) from the Victoria Land Coast,Ross Sea,Antarctica

We report on an accumulation of mummified southern elephant seals (Mirounga leonina) from Inexpressible Island on the Victoria Land Coast (VLC), western Ross Sea, Antarctica. This accumulation is unusual, as elephant seals typically breed and molt on sub‐Antarctic islands further north and do not currently occupy the VLC. Prior ancient DNA analyses revealed that these seals were part of a large, Antarctic breeding population that crashed ~1,000 yr ago. Radiocarbon dates for Inexpressible Island mummies range from 380 to 3,270 yr before present, too old to have been created by Scott's Northern Party in 1912 and varying too widely in age to represent a catastrophic death assemblage. Skeletal measurements reveal that most Inexpressible Island mummies are adult or subadult males. The presence of male elephant seals on Inexpressible Island until several hundred years ago suggests that, at a minimum, it served as a haul‐out site for the large Antarctic population and may have hosted a breeding colony. The conditions that allowed this Antarctic population to use the Ross Sea, the factors spurring its decline, and the implications for the adaptability and sensitivity of the species to environmental change all merit further study.     

Inter-population differences in diving behaviour of adult male southern elephant seals (Mirounga leonina)

Access to different environments may lead to inter-population behavioural changes within a species that allow populations to exploit their immediate environments. Elephant seals from Marion Island (MI) and King George Island (KGI) (Isla 25 de Mayo) forage in different oceanic environments and evidently employ different foraging strategies. This study elucidates some of the factors influencing the diving behaviour of male southern elephant seals from these populations tracked between 1999 and 2002. Mixed-effects models were used to determine the influence of bathymetry, population of origin, body length (as a proxy for size) and individual variation on the diving behaviour of adult male elephant seals from the two populations. Males from KGI and MI showed differences in all dive parameters. MI males dived deeper and longer (median: 652.0?m and 34.00?min) than KGI males (median: 359.1?m and 25.50?min). KGI males appeared to forage both benthically and pelagically while MI males in this study rarely reached depths close to the seafloor and appeared to forage pelagically. Model outputs indicate that males from the two populations showed substantial differences in their dive depths, even when foraging in areas of similar water depth. Whereas dive depths were not significantly influenced by the size of the animals, size played a significant role in dive durations, though this was also influenced by the population that elephant seals originated from. This study provides some support for inter-population differences in dive behaviour of male southern elephant seals.     

Phylogeography of a mite,Halozetes fulvus,reflects the landscape history of a young volcanic island in the sub‐Antarctic

Previous studies of the microarthropods of Marion Island, Southern Ocean, documented high mitochondrial COI (cytochrome c oxidase subunit I) haplotype diversity and significant genetic structure, which were ascribed to landscape subdivision. In this paper we revisit these ideas in light of new geomorphological evidence indicating a major lineament orientated along N26.5°E. Using the microarthropod Halozetes fulvus, we test the hypothesis that the eastern and western sides of the island show different population genetic patterns, corresponding to the previously unrecognized geological separation of these regions, and perhaps also with differences in climates across the island and further landscape complexity. Mitochondrial COI data were collected for 291 H. fulvus individuals from 30 localities across the island. Notwithstanding our sampling effort, haplotype diversity was under‐sampled as indicated by rarefaction analyses. Overall, significant genetic structure was found across the island as indicated by Φ_ST analyses. Nested clade phylogeographical analyses suggested that restricted gene flow (with isolation‐by‐distance) played a role in shaping current genetic patterns, as confirmed by Mantel tests. At the local scale, coalescent modelling revealed two different genetic patterns. The first, characterizing populations on the south‐western corner of the island, was that of low effective population size and high gene flow. The converse was found on the eastern side of Marion Island. Taken together, substantial differences in spatial genetic structure characterize H. fulvus populations across Marion Island, in keeping with the hypothesis that the complex history of the island, including the N26.5°E geological lineament, has influenced population genetic structure. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 131–145.     

Temporal changes in fecundity and age at sexual maturity of southern elephant seals at Marion Island

Our objective was to examine the effect of variation in reproductive parameters on the demography of southern elephant seals at Marion Island. We used age-specific capture probabilities of breeding females in a Cormack-Jolly-Seber context to derive reproductive rates. We found that age at maturity declined and fecundity rates increased as the population declined, indicating a compensatory response. Fecundity rates ranged from 0.03 to 0.29 among 3-year-olds (mean=0.16), 0.18 to 0.50 in 4-year-olds (mean=0.40), and 0.28 to 0.50 in 5-year-olds (mean=0.45). We think that a relative increase in food availability, concomitant with the population decline, promoted earlier sexual maturity correlated with more rapid growth of juveniles when population abundance was lower. It is suggested that the relative importance of fecundity in population regulation in elephant seals has been underestimated. Moreover, it appears that the onset of sexual maturity may be the first demographic variable to change in response to a change in population density.     

MORPHOMETRICS AND BREEDING BIOLOGY OF THE WHITECHINNED PETREL PROCELLARIA AEQUINOCTIALIS AT SUB-ANTARCTIC MARION ISLAND

Berruti, A., Cooper, J. & Newton, I.P. 1995. Morphometrics and breeding biology of the Whitechinned Petrel Procellaria aequinoctialis at sub-Antarctic Marion Island. Ostrich 66: 74–80.

Aspects of adult morphometrics and the breeding biology of the summer-breeding Whitechinned Petrel at sub-Antarctic Marion Island, southern Indian Ocean, are given, based on a study conducted in 1980/91, along with additional observations on breeding success made in 1990191. It is concluded that Whitechinned Petrels at Marion Island are similarly sized and breed in a similar manner to other studied populations of the nominate race. The eradication of cats at Marion Island in 1991 should now lead to a slow population recovery.