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.     

First-year survival of southern elephant seals,Mirounga leonina,at sub-Antarctic Macquarie Island

Juvenile seals branded on the isthmus of Macquarie Island as pups displayed a high degree of philopatry. They returned more often and in greater densities to the northern third of the island within 10 km of their birth sites. Juvenile seals were observed to haul out more frequently and in greater numbers on the east coast as opposed to the west. Juvenile seals typically hauled out on two occasions, once during the winter, and once to moult. The probability of recapturing (resighting) branded and tagged seals was greater during the mid-year haulout. First-year survival estimates were obtained from searches of all Macquarie Island beaches for marked (branded and tagged) seals. From a branded population of 2000 seals, 897 were known to be alive at age 1 year, and minimum first-year survival was calculated at 44.85%. To this minimum estimate was added the number of seals overlooked during systematic and standardised searches of the island, and a revised estimate of 65.60% was calculated. Survival rates calculated using a custom model and a conventional mark-recapture model (MARK) were compared and no differences detected. Actual survival data and probability of sighting estimates were included in the revised estimate of first-year survival of southern elephant seals at Macquarie Island. There were no differences in the number of surviving males and females. Accepted: 25 October 1998     

Counts of southern elephant seals, Mirounga leonina, at Bouvet Island

Southern elephant seals were counted and classified into subjective sex-age classes on a weekly basis during expeditions to Bouvet Island in the austral summers of 1996/1997 and 1998/1999. The expeditions coincided with the moulting period of elephant seals aged one?year and older. The presence of weaned pups at the principal haulout site, Nyrøysa/Westwindstranda, during the latter expedition, indicates that breeding took place here during 1998. Elephant seal counts from previous expeditions are summarised.     

Past and present status of the southern elephant seal (Mirounga leonina) at Macquarie Island

The southern elephant seal population at Macquarie Island has undergone a serious decline since regular surveys were commenced in 1949. Approximately 2,900 cows and 250 bulls were counted in the isthmus study area during the 1985 breeding season. Comparisons with 20 other counts made in the same area between 1949 and 1984 showed that, although there was considerable fluctuation between the years, the number of seals ashore has dropped at an average rate of 2.1% per year, resulting in a net decrease of approximately 50% for both males and females. This is similar to the ratio of decline of elephant seal populations in the southern Indian Ocean. The census information from all major elephant seal populations was reviewed and it was concluded that there may be a common factor, or group of factors, acting to reduce the Macquarie Island and Indian Ocean populations, while the populations of the South Atlantic seem to be stable. Several potential explanations for these observations are advanced, but it is concluded that a greater knowledge of the ecology of the seals is needed if the declines are to be understood.     

The annual cycle of the epididymis of the elephant seal (Mirounga leonina) at Macquarie Island

The tubules of the head and body of the elephant seal epididymis undergo large increases in diameter and principal cell height for the duration of the breeding season, and regress at the conclusion of breeding. The tubules of the tail show a lesser development, and only towards the end of breeding. Spermatozoa, first produced in the testis in August, reach the tail of the epididymis in September, and are present in large numbers throughout the epididymis in October and November. In December, the first month of sexual quiescence following the breeding season, sperm are almost totally absent from the epididymis.     

The annual cycle of the testis of the elephant seal (Mirounga leonina) at Macquarie Island

The testis of the Southern elephant seal demonstrates seasonal changes in weight, with highest values early in the breeding season (September-November) and lowest values in mid-winter (May-June). Weight changes originate in the seminiferous tubules, there being little variation in the interstitial tissue.
Spermatogenesis begins in August, one month before the breeding season, and stops in November. Testicular testosterone concentration is significantly elevated in the months July-September. Plasma testosterone concentration is high only in September, the first month of breeding.     

Climate influences on female survival in a declining population of southern elephant seals (Mirounga leonina)

The Southern Ocean has been disproportionately affected by climate change and is therefore an ideal place to study the influence of changing environmental conditions on ecosystems. Changes in the demography of predator populations are indicators of broader shifts in food web structure, but long‐term data are required to study these effects. Southern elephant seals (Mirounga leonina) from Macquarie Island have consistently decreased in population size while all other major populations across the Southern Ocean have recently stabilized or are increasing. Two long‐term mark‐recapture studies (1956–1967 and 1993–2009) have monitored this population, which provides an opportunity to investigate demographic performance over a range of climatic conditions. Using a 9‐state matrix population model, we estimated climate influences on female survival by incorporating two major climatic indices into our model: The Southern Annular Mode (SAM) and the Southern Oscillation Index (SOI). Our best model included a 1 year lagged effect of SAM and an unlagged SOI as covariates. A positive relationship with SAM1 (lagged) related the previous year''s SAM with juvenile survival, potentially due to changes in local prey availability surrounding Macquarie Island. The unlagged SOI had a negative effect on both juvenile and adult seals, indicating that sea ice dynamics and access to foraging grounds on the East Antarctic continental shelf could explain the different contributions of ENSO events on the survival of females in this population.     

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.     

The dynamics of male harem dominance in southern elephant seals (Mirounga leonina) at the South Shetland Islands

Breeding chronology, harem structure and changes in male harem dominance were studied at Stranger Point, Isla 25 de Mayo/King George Island, principally by extensive field census work during the 2003 breeding season. Males were individually identified and their size estimated by using a photogrammetric method. Peak female haul out for the population occurred on 31 October, when a total of 276 females were observed along 7 km of coastline, distributed in ten harems with a median size of 16 females. Overall sex ratio and harem sex ratio for the breeding population were 1:6.7 and 1:10.6, respectively. A total of 33 males were identified associated with harems. Male size conferred an advantage in terms of dominance hierarchy, since dominant males (4.91±0.15 m) were significantly longer than subordinate males (4.63±0.19 m). Harems were dominated by an average of 4.5 (range 2–7) different males during the breeding season. Elephant seals at Stranger Point breed in very low density aggregations. The main breeding events in this population occurred later than at other breeding sites, which agrees with previous observations in the area. Male movement among harems suggests that differences in mating success among males could be achieved through their different behaviours.     

Minimum population size estimates demonstrate an increase in southern elephant seals (Mirounga leonina) on Livingston Island, maritime Antarctica

Southern elephant seals (Mirounga leonina) are apex predators of marine Antarctic food webs, and variations in their populations have been linked to environmental changes. Consequently, measuring and reporting the status of elephant seal populations provide insights into the environmental status of Antarctica. Here, we present new information on the size of the elephant seal subpopulation on Byers Peninsula (Livingston Island, South Shetland Islands, maritime Antarctica). Based on a total count of 1,510 pups, we estimated a total subpopulation size of 5,530 individuals by using a conversion factor of 3.5. This represents an increase of 150 % since the subpopulation was first counted 30 years ago. Based on this finding, we hypothesize that the overall South Georgia stock, to which the subpopulation we estimated on Byers Peninsula belongs, could be increasing instead of remaining stable as previously thought.     

Aggression and sexual activity of male Southern elephant seals, Mirounga leonina

The agonistic and sexual activity of individual male Southern elephant seals (Mirounga leonina) was studied during the breeding season at South Georgia. Harem bulls were older and larger than non-harem bulls and, although size and age are related, harem bulls were also larger than non-harem bulls of the same age. Large body size conferred advantages in fighting and the agonistic relationships of the bulls gave rise to a dominance hierarchy with access to harems and activity within harems, being determined by rank. Vocalizations were the most highly rank-related aggressive behaviours. The most common vocalization, the roar, probably functioned in both individual recognition and size assessment. Over 90% of encounters of high-ranked bulls were "walkovers" and only 4% of 4003 agonistic interactions nvolved physical contact.     

Local weather and body condition influence habitat use and movements on land of molting female southern elephant seals (Mirounga leonina)

Southern elephant seals (Mirounga leonina) are known to move and aggregate while molting, but little is known about their behavior on land during this time. In this study, 60 adult females were monitored (23 with GPS tags) during four molting seasons, between 2012 and 2016 at Kerguelen Archipelago, Indian Ocean. Population surveys were recorded each year (N = 230 daily counts), and habitat use was analyzed in relation to the stage of the molt and local weather. Based on stage of molt, habitat use, and movements on land, we classified the molt of elephant seals into three phases: (1) a “search phase” at the initial stage of molt when grass and wallow habitats were used and characterized by greater mean distances travelled on land per day compared with the two other phases; (2) a “resident phase”: during initial and mid‐stage of molt when animals were found in grass and wallow habitats but with less distance moved on land; and (3) a “termination phase” at the final stage of molt where grass and beach habitats were occupied with no change in distances. Windchill and solar radiation influenced individual distances moved per day (mean 590 ± 237.0 m) at the mid‐ and final stage of molt such that animals travelled greater distances on days of low windchill or high solar radiation. Individual variation in distance moved and relative habitat use were also linked to body mass index (BMI) at arrival on the colony, as females with higher BMI moved less and preferred beach habitat. Moreover, the individual rate of molt increased with the use of wallows. Aggregation rate tended to be negatively correlated with distances moved. We therefore suggest that individuals face an energetic trade‐off while molting, balancing energy expenditure between movement and thermoregulation.     

Sex-specific mercury levels in skin samples of southern elephant seals (Mirounga leonina) at Isla 25 de Mayo (King George Island), Antarctic Peninsula

The southern elephant seal (SES; Mirounga leonina) has a circumpolar distribution, breeding mainly on sub-Antarctic islands and making long trips between breeding or molting and foraging areas. Most individuals from colonies in the South Shetland Islands (western Antarctic Peninsula; WAP) are distributed in Antarctic Specially Protected Areas (ASPA). Despite these protected habitats, pollutants can reach such remote areas far away from emission sources, affecting local fauna. To assess possible mercury (Hg) contamination in SES, we analyzed skin samples collected from free-ranging molting individuals using the remote biopsy PAXARMS system in Isla 25 de Mayo/King George Island (62°15′S, 58°39′W; ASPA 132). Hairless skin samples were analyzed to determine total-Hg (THg) concentrations, which ranged between 145 ng/g and 1,915 ng/g (M = 730, SD = 388 ng/g), showing significant differences between sexes, with adult-females having higher concentrations (range = 306–1,915, M = 859, SD = 427 ng/g dw) than subadult-males (range = 145–1,645, M = 629, SD = 329 ng/g dw). These differences may be explained mainly by feeding-niche partitioning between sexes. Females prefer mesopelagic prey or prey associated with sea-ice in the WAP, which are enriched in methylmercury. These results provide insight regarding Hg contamination in top Antarctic predators like SES, and the need to monitor for potential effects of Hg contamination in Antarctic marine mammals.     

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.     

Energy gain and loss during lactation and postweaning in southern elephant seal pups (Mirounga leonina) at King George Island

Deuterium-labeled water was used to measure changes in the proximate body composition during the lactation period and after weaning in southern elephant seal pups at King George Island, South Shetland Islands, Antarctica. During the lactation period (23.0 ± 1.4 days) pups gained a mean of 4.9 ± 0.5 kg/day (n=7). Of the total mass gain (112 ± 8 kg), 38% was water, 48% was fat, and 11% was protein. This represented an increase in total body gross energy of 2437 ± 145 MJ. The proportion of body mass represented by fat was less than 2% at birth, increasing to 35 ± 2% at weaning. We followed the pups during a mean period of 36 ± 3 days after weaning. During this period, pups had a mean loss of 1.21 ± 0.10 kg/day (n=7) comprising 39% water, 48% fat, and 12% protein. The energy cost over this period was 952 ± 168 MJ, which represented, on average, 39% of the total energy gained during the suckling period. Accepted: 3 January 2000     

Mass transfer from mothers to pups and mass recovery by mothers during the post-breeding foraging period in southern elephant seals (Mirounga leonina) at King George Island

Mass transfer from mother to pup during the lactation period, and mass recovery for the same females during the foraging period were measured in the southern elephant seal at King George Island, Antarctica. During the 19.2 ± 0.9-day lactation period measured (which represented 87% of the entire nursing), females lost a mean mass of 10.56 ± 1.76 kg/day (n = 27), while their pups gained a mean mass of 5.27 ± 1.1 kg/day. There was a correlation between daily body weight gain in pups and daily weight loss by their mothers. Pup weaning mass was positively related to maternal post-partum mass. Serial samples showed that weight losses by females and gains by their pups were not linear over lactation, but showed lower values at the beginning and at the end of lactation. During the 60.5 ± 6.2-day foraging phase between the end of lactation and molt, females gained 2.21 ± 0.65 kg/day (n = 12), or 54% of the mass lost during nursing. Growth rates reported here are higher than those reported in other breeding sites. However, the ratio of body mass loss by females to gain by their pups was similar, suggesting that higher growth rates and greater weaning mass at South Shetland are due to a higher mean weight of females on arrival at this breeding site. The foraging period was shorter and the mass gained greater than those measured at South Georgia; this could be related to relatively shorter distances to foraging areas. Received: 20 September 1996 / Accepted: 28 April 1997