Fasting metabolism in Antarctic fur seal (Arctocephalus gazella) pups.

The metabolism of 52-73-day old Antarctic fur seal pups from Bird Island, South Georgia, was investigated during fasting periods of normal duration while their mothers were at sea foraging. Body mass decreased exponentially with pups losing 3.5-3.8% of body mass per day. Resting metabolic rate also decreased exponentially from 172-197 ml (O2) x min(-1) at the beginning of the fast and scaled to M(b)(0.74) at 2.3 times the level predicted for adult terrestrial mammals of similar size. While there was no significant sex difference in RMR, female pups had significantly higher (F(1,18)=6.614, P<0.019) mass-specific RMR than male pups throughout the fasting period. Fasting FMR was also significantly (t(15)=2.37, P<0.035) greater in females (823 kJ x kg(-1) x d(-1)) than males (686 kJ x kg(-1) x d(-1)). Average protein turnover during the study period was 19.3 g x d(-1) and contributed to 5.4% of total energy expenditure, indicating the adoption of a protein-sparing strategy with a reliance on primarily lipid catabolism for metabolic energy. This is supported by observed decreases in plasma BUN, U/C, glucose and triglyceride concentrations, and an increase in beta-HBA concentration, indicating that Antarctic fur seals pups adopt this strategy within 2-3 days of fasting. Mean RQ also decreased from 0.77 to 0.72 within 3 days of fasting, further supporting a rapid commencement of protein-sparing. However, RQ gradually increased thereafter to 0.77, suggesting a resumption of protein catabolism which was not substantiated by changes in plasma metabolites. Female pups had higher TBL (%) than males for any given mass, which is consistent with previous findings in this and other fur seal species, and suggests sex differences in metabolic fuel use. The observed changes in plasma metabolites and protein turnover, however, do not support this.     

Male reproductive strategy and the importance of maternal status in the Antarctic fur seal Arctocephalus gazella

Abstract. Although mammalian mating systems are classically characterized in terms of male competition and polygyny, it is becoming increasingly apparent that alternative male strategies and female choice may play important roles. For example, females who mate with males from a dominant dynasty risk producing inbred offspring. Many pinnipeds are highly polygynous, but in some species alternative male strategies such as aquatic mating appear to be important, even when behavioral observations suggest strong polygyny. Here, we analyze male reproductive success in the Antarctic fur seal Arctocephalus gazella , an otariid described behaviorally as being highly polygynous, by combining a microsatellite paternity analysis spanning seven consecutive breeding seasons with detailed behavioral data on both sexes. Territorial males fathered 59% of 660 pups analyzed from our study colony. Male reproductive skew was considerable, with a quarter of all paternities assigned to just 12 top individuals on a beach where mean annual pup production was 635. Most males were successful for only a single season, but those able to return over successive years enjoyed rapidly increasing success with each additional season of tenure. We found no evidence of alternative male reproductive tactics such as aquatic or sneaky terrestrial mating. However, paternity was strongly influenced by maternal status. Females observed on the beach without a pup were significantly less likely to conceive to a sampled territorial male than equivalent females that did pup. In addition, their pups carried combinations of paternal alleles that were less likely to be found on the study beach and exhibited lower levels of shared paternity. Thus, from a territorial male's perspective, not all females offer equal opportunities for fertilization.     

Temporal patterns of milk production in Antarctic fur seals (Arctocephalus gazella)

The timing of milk production in Antarctic fur seals was studied at Bird Island, South Georgia. Like all lactating otariid seals (Pinnipedia: Otariidae), Antarctic fur seal females alternate between short nursing periods ashore and regular foraging trips to sea. Females do not necessarily return to the colony with full mammae, which indicates that mammary volume capacity is unlikely to limit foraging trip duration. Upon arrival at the colony, milk fat (r²= 0.33, P < 0.04) and protein (r²= 0.60, P < 0.002) content were positively correlated to the time spent at sea. A similar trend was observed in the milk produced on land. The rate of milk energy production was much lower at sea (5.02 ± 0.05 MJ day^-1) than on land (23.66 ± 4.4 MJ^-1 day^-1). The rate of milk energy production during the foraging trip was negatively correlated to the time spent at sea (r²= 0.29, P < 0.05), whereas the rate of milk energy production on land was positively correlated (r²= 0.61, P < 0.001) to the duration of the preceding foraging trip. The total amount of milk energy delivered to the pup during each twoday nursing period was positively correlated (r²= 0.60, P < 0.002) to the duration of the previous foraging trip. The overall rate of milk energy delivery, however, was independent of foraging trip duration. This accords with previous observations that the growth rates of Antarctic fur seal pups are unaffected by maternal foraging trip duration patterns.     

Variation in plasma leptin levels in response to fasting in Antarctic fur seals (Arctocephalus gazella)

Plasma leptin levels were determined in 8 lactating female and 20 pup Antarctic fur seals (Arctocephalus gazella) during fasting periods of normal duration. Plasma leptin levels ranged from 1.35 3.19 ng x ml(-1) in lactating females and 1.79-4.80 ng x ml(-1) in pups and were not positively correlated with body mass or condition. A negative trend, however, was observed between plasma leptin levels and body condition in lactating females upon their arrival at the colony following a foraging trip (beginning of fast). In accordance with findings in other species, plasma leptin levels dropped significantly (P < 0.02) in response to the 17-19% drop in body mass experienced by pups during fasting. In contrast, plasma leptin levels in lactating females increased during the first 24 h of fasting before decreasing throughout the remaining 48 h of the fast. This unexpected result could be due to the high level of energy expenditure by seals as they swim back to the colony (i.e. post-exercise response) or may be influenced by the intense suckling activity experienced by females during the onshore fasting periods. The results of this study support recent findings in other carnivore species which suggest the primary physiological role of leptin in these species may not necessarily be as a signal of the magnitude of body energy reserves.     

Exploring the relationship between parental relatedness and male reproductive success in the Antarctic fur seal Arctocephalus gazella

Recent genetic studies of natural populations have shown that heterozygosity and other genetic estimates of parental relatedness correlate with a wide variety of fitness traits, from juvenile survival and parasite resistance to male reproductive success. Many of these traits involve health and survival, where the underlying mechanism may involve changes in the effectiveness of the immune system. However, for traits such as reproductive success, the likely mechanisms remain less obvious. In this paper, we examine the relationship between heterozygosity and a range of traits that contribute to male reproductive success, including time spent on territories and competitiveness. Our analysis is based on observational and genetic data from eight consecutive breeding seasons at a colony of the Antarctic fur seal, Arctocephalus gazella. Overall, male reproductive success was found to correlate strongly with internal relatedness (IR, a form of heterozygosity). When different components of success were analyzed, we found that IR correlates independently with reproductive longevity, time spent ashore, and competitive ability per unit mating opportunity on the study beach, with more heterozygous males being more successful. Behavioral observations were sufficiently detailed to allow examination of how daily mean IR values for males present on the beach varied within seasons and from year to year. Again, significant variation was found both among and within seasons, with more homozygous males appearing less able to hold territories in poor seasons when pup production is low and, within a season, at both the start of the season and to some extent around the peak of female estrus. Finally, we tested whether the benefits of high heterozygosity are due mainly to a genomewide effect (e.g. inbreeding depression) or to single locus heterosis by asking whether the relationship between IR and male success was robust to the removal of any single locus or to any pair of loci. Since the relationship remained significant in all cases, we favor a multilocus explanation for the effects we report.     

Kin selection may influence fostering behaviour in Antarctic fur seals (Arctocephalus gazella)

Fostering confers obvious advantages to the offspring but is seemingly costly to the caregiver. Such behaviour is particularly paradoxical in seals where the energetic investment in milk is very high and has led to the suggestion that this behaviour may have evolved through either kin selection or reciprocity. We used a combination of genetic and behavioural data to investigate whether kin selection plays a role in the fostering behaviour observed in a well-studied population of Antarctic fur seals (Arctocephalus gazella) from Bird Island, South Georgia. Genotypic data from eight highly polymorphic microsatellite markers were used to estimate relatedness among mother-pup pairs, foster mother-pup pairs and the total population. Mean relatedness was found to be significantly higher for foster mother-pup pairs than that observed for the total population, suggesting that kin selection could have a role in the maintenance of fostering behaviour in this species.     

Ontogeny of aquatic behaviours in Antarctic fur seal (Arctocephalus gazella) pups in relation to growth performances at Kerguelen Islands

In diving marine predators, such as pinnipeds, the development of diving and foraging skills prior to weaning might be critical to post-weaning survival. Here, we examined the effect of pup mass growth on the amount of time devoted to aquatic activities and the dive performance of Antarctic fur seal, Arctocephalus gazella, pups on Kerguelen Island. Maternal attendance and mass-specific growth rate were assessed for 85 pups. Two types of monitoring were applied: visual observations of behaviours for 60 pups and the deployment of time-depth recorders (TDRs) on 19 female pups. At approximately 2 months of age, pups demonstrated minimal diving behaviour, but displayed considerable aquatic activity. While mothers were foraging at sea, pups fasted on land (6.0 ± 1.3 d). As the mass-specific growth rate was different between sexes, only data on female pups were analysed (n = 31). Mass-specific growth rate was related to maternal attendance patterns and impacted the amount of time allocated by pups to aquatic activities. The time spent in the water by pups was quadratically related to fasting progress. This study shows the importance of growth and fasting progress on the quantity of time pups devoted to aquatic activities. Our results suggest that greater post-weaning survival of heavier pups may be due not only to their greater body reserves, as reported in several studies, but also possibly to from their greater aquatic skills and physiological adaptations developed during the suckling period.     

Population size and age determination in the Antarctic Fur seal Arctocephalus gazella

The population of Antarctic Fur seals Arctocephalus gazella at South Georgia is increasing rapidly and is therefore of great interest. Investigations of the population depend on two main techniques.
(1) Population assessment, because the population size is now too large for direct counts to be completely reliable, and serious underestimates are appearing in areas of high density. Aerial photography was used but needs further refinement before it becomes a consistently useful technique. Marking all pups on sample beaches was largely unsuccessful because pups moved from beach to beach before they could all be marked. A mark–recapture method was finally adopted and indicated that the numbers of pups present may be up to 54% higher than the numbers actually counted.
(2) The process of age determination from tooth characters, which is more difficult for Fur seals than other pinnipeds. The preparation and interpretation of the teeth of breeding cows is described, based on eleven specimens of known age. The most accurate results are obtained from whole teeth up to the age of 6, but thereafter interpretation of cement and dentine layers in thin sections must be used. It is concluded that while young animals are aged quite accurately, there is probably a tendency to underestimate the age of seals of more than 9 years.     

Lipid composition of blood platelets and erythrocytes of southern elephant seal (Mirounga leonina) and antarctic fur seal (Arctocephalus gazella)

Erythrocyte and blood platelet phospholipid compositions were studied in three elephant seals and two fur seals, two species of marine mammals living in the Subantarctic region feeding on preys rich in (n-3) polyunsaturated fatty acids. Results were compared with those reported for related species and humans. In erythrocytes, the phospholipid (PL) and cholesterol (CHOL) contents were lower in pinnipeds than in humans. Phosphatidylcholine (PC) levels were higher in elephant seals than in fur seals, with a reverse trend for phosphatidylethanolamine (PE) and phosphatidylserine (PS). Both species had lower SM/PC ratios and PE plasmalogen concentrations than human. Erythrocytes were richer in (n-3) fatty acids (FA) in pinnipeds than in humans. In platelets, the PL content was lower and the CHOL content higher in elephant seals than in humans or in other phocid seal species studied to date. The SM/PC ratio was much higher than in other seal species or in man. In both species, the proportion of PE plasmalogens was higher in platelets than in erythrocytes. PL were more saturated in elephant seals than in fur seals. These results suggest that the erythrocytes and platelets of wild marine mammals may prove useful models to study the influence of dietary lipids on the structure and hemostatic function of these cells.     

The diet of the Antarctic fur seal Arctocephalus gazella at Harmony Point, Nelson Island, South Shetland Islands

The diet of non-breeding male Antarctic fur seals (Arctocephalus gazella) was investigated at Harmony Point, Nelson Island, South Shetland Islands, by the analysis of 18 and 33 scats collected during February 1996 and 1997 respectively. Overall, fish were the most frequent prey (74.5%) and predominated by mass (54.4%), whereas krill predominated by number (94.2%). This coincides well with the pattern observed in 1997, but in 1996 krill was the most important prey by number and mass (50.2%). The importance of the remaining taxa represented in the samples (octopods, hyperiids and bivalves) was negligible. Among fish, myctophids represented 85.2% of the fish mass, with Gymnoscopelus nicholsi and Electrona antarctica being the main prey. These two species predominated in 1997, whereas the channichthyid Cryodraco antarcticus and the nototheniid Gobionotothen gibberifrons were dominant in 1996. The importance of the myctophids as prey of the Antarctic fur seal is discussed. Received: 7 October 1997 / Accepted: 24 May 1998     

The composition of Australian fur seal (Arctocephalus pusillus doriferus) milk throughout lactation.

The proximate chemical composition of milk was determined throughout lactation in the Australian fur seal (Arctocephalus pusillus doriferus Wood Jones), a temperate species with an 11-mo lactation period typical of most temperate otariids. Average lipid and protein contents were 42% and 10%, respectively, which is similar to that recorded for the polar otariid species but higher than reported in other temperate, long-lactation species. Milk composition, however, varied substantially throughout lactation, with lipid content rising from 30% soon after parturition to 50% at 230 d postpartum before decreasing to 45% toward weaning. The trend in water content was opposite to that of lipid, while protein content increased only slightly during lactation from 10% to 12%. The peak in lipid content occurred at approximately 70% of the way through lactation, similar to that found in the Australian sea lion and several phocid seal species. Significant positive relationships were found between milk lipid content and both the duration of the preceding foraging trip and body mass. A highly significant and close correlation was found between milk water and lipid contents such that gross energy content may be accurately predicted from water content alone. Similar predictive equations have been found for several other otariid and phocid species, but these appear to differ between phylogenetic groups.     

Low reproductive success in territorial male Antarctic fur seals (Arctocephalus gazella) suggests the existence of alternative mating strategies

Microsatellites were used to conduct an analysis of paternity of Antarctic fur seals (Arctocephalus gazella) from Bird Island, South Georgia. At most, only 28% of pups at our study site could be assigned a father, even though the majority (approximately 90%) of candidate males within this colony were sampled. The behavioural and genetic evidence from this study suggests that a number of alternative mating strategies may exist within this fur seal population. Holding a land-based territory conferred an advantage to male reproductive success. However, this advantage was much smaller than expected from behavioural observations. At least 70% of fur seal pups born at our study site in a given year are not fathered by males who held a territory or were observed copulating with females in the previous year, implying that there exists a pool of males that seldom venture ashore at this site. To explain this discrepancy we suggest that female choice is an integral component of the Antarctic fur seal mating system and that aquatic mating may play a much larger role in the Antarctic fur seal than previously thought.     

Foraging routes of Antarctic fur seals (Arctocephalus gazella) investigated by the concurrent use of satellite tracking and time-depth recorders

Little is known about movement behaviour in terms of route choice in Antarctic fur seals (Arctocephalus gazella). We deployed satellite transmitters and time-depth recorders simultaneously on 11 animals, and time-depth recorders with a speed recorder on 10 animals, to investigate the foraging routes of Antarctic fur seals belonging to a colony located at Iles Kerguelen (Southern Indian Ocean). The study took place during the 1997/1998 austral summer, and results indicate a preferred foraging area, with two main strategies in route choice apparent during foraging trips. In one strategy seals tended to reach an apparently known foraging ground and stopped there to feed. In the other strategy, animals performed looped trips, foraging en route and probably searching for a food patch better than the one previously exploited. Accepted: 13 September 1999     

Postsealing genetic variation and population structure of two species of fur seal (Arctocephalus gazella and A. tropicalis)

Commercial sealing in the 18th and 19th centuries had a major impact on the Antarctic and subantarctic fur seal populations (Arctocephalus gazella and A. tropicalis) in the Southern Ocean. The intensive and unrestricted nature of the industry ensured substantial reductions in population sizes and resulted in both species becoming locally extinct at some sites. However, both species are continuing to recover, through the recolonization of islands across their former range and increasing population size. This study investigated the extent and pattern of genetic variation in each species to examine the hypothesis that higher levels of historic sealing in A. gazella have resulted in a greater loss of genetic variability and population structure compared with A. tropicalis. A 316-bp section of the mitochondrial control region was sequenced and revealed nucleotide diversities of 3.2% and 4.8% for A. gazella and A. tropicalis, respectively. There was no geographical distribution of lineages observed within either species, although the respective PhiST values of 0.074 and 0.19 were significantly greater than zero. These data indicate low levels of population structure in A. gazella and relatively high levels in A. tropicalis. Additional samples screened with restriction endonucleases were incorporated, and the distribution of restriction fragment length polymorphism (RFLP) and sequence haplotypes were examined to identify the main source populations of newly recolonized islands. For A. tropicalis, the data suggest that Macquarie Island and Iles Crozet were probably recolonized by females from Marion Island, and to a lesser extent Ile Amsterdam. Although there was less population structure within A. gazella, there were two geographical regions identified: a western region containing the populations of South Georgia and Bouvetoya, which were the probable sources for populations at Marion, the South Shetland and Heard Islands; and an eastern region containing the panmictic populations of Iles Kerguelen and Macquarie Island. The latter region may be a result of a pronounced founder effect, or represent a remnant population that survived sealing at Iles Kerguelen.     

Long-term variability in the abundance of Antarctic fur seals Arctocephalus gazella at Signy Island, South Orkneys

The number of Antarctic fur seals Arctocephalus gazella hauled out at Signy Island in the South Orkneys was monitored annually between 1977 and 2008. Over the study period seal abundance showed a tenfold increase, from a minimum of 1,643 seals in 1978 to a maximum of 21,303 in 1994. The majority of individuals observed were young adult males, likely to be migrants from South Georgia, with small numbers of female seals and only 65 pups recorded during the survey period. Variability in counts showed a similar pattern to Laurie Island, also in the South Orkneys archipelago, suggesting a similar annual immigration of seals to these two islands. The date of first seal arrival was correlated with the date of fast-ice breakout at Factory Cove, Signy Island, and years in which break out was exceptionally late (>21 December) corresponded with years of reduced seal abundance. While the presence of fast-ice during the early breeding season may currently inhibit the establishment of a major breeding population of fur seals at Signy Island, it is important that routine monitoring should continue, particularly in the light of current patterns of climate warming in the Antarctic.     

The diet of Antarctic fur seals,Arctocephalus gazella,during the summer-autumn period at Mossman Peninsula,Laurie Island (South Orkneys)

Summary From mid January to April 1988 a total of 105 faecal samples of non breeding male fur seals, Arctocephalus gazella, was collected at Mossman Peninsula, Laurie Island. Examination of scats containing prey remains showed that fur seals fed mainly on krill, occurring in 100% of samples but fish were also a common food item (78.8%). Myctophids constituted more than 90% of fish taken by fur seals. Squid beaks occurred in 34.3% of scats, being more common in the autumn period.     

Tooth growth in male Antarctic fur seals (Arctocephalus gazella) from South Georgia: an indicator of long-term growth history

Growth of upper canine teeth of male Antarctic fur seals ( Arctocephalus gazella ) which died of natural causes at Bird Island, South Georgia, was quantified from measurements of annual layers in longitudinal sections of teeth. Mean age at death was 7.69±0.07 years and this showed a small but significant increase through the period when samples were collected (1972/73–1988/89). There were significant correlations between morphometrics of teeth and those of seals, suggesting that tooth growth provided an indication of body growth. Tooth growth rate was lowest in seals which died early (age 4 years) and increased with age at death. Changes in the growth pattern of teeth suggested that fur seals which became sexually mature early also died early. Tooth growth layers deposited in each calendar year were compared with the expected layer depth based on a linear relationship between layer depth and age at which each layer was deposited. There was significant variation in the depth of tooth growth layers deposited in different years, suggesting that growth was greater in some years than others. No trends in cohort strengths were detected, but particularly poor years for growth were closely related to years in which reproductive performance was also observed to be low. Variations in growth from 1967/68 to 1987/88 were correlated significantly (P < 0.008) with the Southern Oscillation Index of climatic variation.