Milking strategy in subantarctic fur seals Arctocephalus tropicalis breeding on Amsterdam Island: evidence from changes in milk composition.

Milk composition was investigated throughout the 10-mo pup-rearing period in subantarctic fur seals (Arctocephalus tropicalis) breeding on Amsterdam Island. The mean milk composition was 42.8% +/- 5.7% lipid, 12.1% +/- 1.5% protein, and 42.6% +/- 7.3% water. Subantarctic fur seals breeding on Amsterdam Island produced one of the richest milks ever reported in otariids (20.4 +/- 2.9 kJ/g), with lipid content contributing 85% of total gross energy. The high lipid levels measured in the milk of subantarctic fur seals breeding on Amsterdam Island is consistent (i) with the relatively long time lactating females spend at sea, due to the relatively poor local trophic conditions near the colony that necessitate that they travel long distances to reach the foraging grounds, and (ii) with the consequently short time mothers spend with their pups ashore. Milk composition changed according to the time mothers were fasting ashore: milk produced during the first 2 d spent ashore, when more than 80% of milk transfer occurred, had higher levels of lipids, proteins, and gross energy than milk produced later during the visit ashore, suggesting that the pups were fed with two types of milk during a suckling period. Throughout the year, mothers in good condition produced milk of higher lipid content than others, suggesting that individual foraging skills contribute to enhance milk quality. Milk lipid and gross energy content varied with pup age, according to quadratic relationships, increasing during the earlier stages of lactation before reaching asymptotic values when pups were 180 d old. The stage of lactation appears to be a better predictor of milk lipid content than the duration of the preceding foraging trip, suggesting that either changes in the nutritional requirements of the pup and/or seasonal changes in trophic conditions act on milk composition. These changes in milk quality may also be related to changes in maternal care; lactating subantarctic fur seals apparently reallocate their body reserves toward gestation rather than lactation at the end of the pup-rearing period.     

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.     

Killer whale predation on subantarctic fur seals at Prince Edward Island, Southern Indian Ocean

Killer whales at subantarctic Marion Island have been subjected to several scientific studies. In contrast, up until recently, there has been only one record of these animals documented for neighbouring Prince Edward Island. We here report on killer whale observations at Prince Edward Island during March 2012. During 3?days of opportunistic observations at a fur seal colony on the island, killer whales were sighted on six occasions. These probably represented three different pods numbering 11 individuals in total. During all sightings, individuals were seen hunting subantarctic fur seal pups, with four successful predatory events observed.     

Ménage à trois on Macquarie Island: hybridization among three species of fur seal (Arctocephalus spp.) following historical population extinction

Human-induced changes to natural systems can cause major disturbances to fundamental ecological and population processes and result in local extinctions and secondary contacts between formerly isolated species. Extensive fur seal harvesting during the nineteenth century on Macquarie Island (subantarctic) resulted in extinction of the original population. Recolonization by three species has been slow and complex, characterized by the establishment of breeding groups of Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalus tropicalis) and presumed nonbreeding (itinerant) male New Zealand fur seals (Arctocephalus forsteri). One thousand and seven pups from eight annual cohorts (1992-2003) were analysed using mitochondrial control region data (RFLP) and 10 microsatellite loci to estimate species composition and hybridization. Antarctic fur seals predominated, but hybridization occurred between all three species (17-30% of all pups). Involvement of New Zealand fur seals was unexpected as females are absent and males are not observed to hold territories during the breeding season. The proportion of hybrids in the population has fallen over time, apparently owing to substantial influxes of pure Antarctic and subantarctic individuals and non-random mating. Over 50% of New Zealand hybrids and 43% of Antarctic-subantarctic hybrids were not F(1), which indicates some degree of hybrid reproductive success, and this may be underestimated: simulations showed that hybrids become virtually undetectable by the third generation of backcrossing. While human impacts seem to have driven novel hybridization in this population, the present 'time slices' analysis suggests some biological resistance to complete homogenization.     

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)·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 (t₁₅=2.37, P<0.035) greater in females (823 kJ·kg⁻¹·d⁻¹) than males (686 kJ·kg⁻¹·d⁻¹). Average protein turnover during the study period was 19.3 g·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 β-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.     

Fur seals at Macquarie Island: post-sealing colonisation,trends in abundance and hybridisation of three species

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The first breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954–2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is significant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been affected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.     

Multiple mating strategies explain unexpected genetic mixing of New Zealand fur seals with two congenerics in a recently recolonized population

Human impacts on natural systems can cause local population extinctions, which may promote redistribution of taxa and secondary contact between divergent lineages. In mammalian populations that have mating systems shaped by polygyny and sexual selection, the potential for hybridization to ensue and persist depends on individual and demographic factors. At Macquarie Island, a recently formed fur seal population is comprised of both sexes of breeding Antarctic (Arctocephalus gazella) and subantarctic (A. tropicalis) fur seals, and an itinerant collection of male New Zealand fur seals (A. forsteri), presumed to be non-breeders due to their absence from principle breeding areas. The mating system of the three species is described as resource-defence polygyny: males defend beach territories containing breeding females for exclusive mating rights. A recent genetic study identified a high level of hybridization in the population (17-30%), unexpectedly involving all three species. This study examined the source of involvement in breeding by A. forsteri with respect to mating strategies operating in the population. Ninety-five (10%) pups born from 1992 to 2003 were genetically identified as New Zealand hybrids. Most resulted from reproduction within territories by New Zealand hybrids of both sexes, although some were conceived extra-territorially, indicating that males successfully utilize strategies other than territory holding to achieve paternities. Female reproductive status influenced mating partner and mating location, and females without pups were more likely to conceive extra-territorially and with A. forsteri males. This study illustrates an important consequence of low heterospecific discrimination in a sympatric population of long-lived mammals.     

Milk intake and energy expenditure of free-ranging northern fur seal, Callorhinus ursinus, pups

Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic investment, influences survival and growth. A number of studies have examined milk intake in otariids, but few have examined milk intake over the entire lactation period, and none has independently measured energy expenditure concurrent with milk intake. We concurrently examined milk intake, field metabolic rate (FMR), and body composition of 41 pups over the entire lactation interval in 1995 and 1996 on St. Paul Island, Alaska. One hundred two metabolic measurements were obtained with isotope dilution methods. Mean milk intake did not differ annually but increased with age and mass, ranging from 3,400+/-239 to 6,780+/-449 (+/-SE) mL per suckling bout. Milk energy consumption did not vary with age on a mass-specific basis. No differences were detected in milk volume consumed by male and female pups, either absolutely or on a mass-specific basis. Mass-specific FMR peaked during molting, was lowest postmolt, and did not vary by sex. Pups in 1995 had lower FMR than pups in 1996 and were also fatter. Mean milk energy utilized for maintenance metabolism decreased over time from 77% to 43% in 1995 and remained at 71% in 1996. Pup body mass was negatively correlated with the percentage of total body water and positively correlated with the percentage of total body lipid (TBL). Pups increased the percentage of TBL from 16% to 37%. Northern fur seal pups increased energy intake over lactation, while concurrent changes in body composition and pelage condition resulted in mass-specific metabolic savings after the molt.     

Early-life density-dependence effects on growth and survival in subantarctic fur seals

Understanding the regulation of natural populations has been a long-standing research program in ecology. Current knowledge on marine mammals and seabirds is biased toward the adult component of populations and lacking are studies investigating the juvenile component. Our goal was to estimate demographic parameters on the pre-weaning stage of a subantarctic fur seal (Arctocephalus tropicalis) population on Amsterdam Island, suspected to be regulated by density-dependence. The influence of abundance on growth parameters (length and weight) and survival was assessed over a study period spanning 16 years. We evidenced a negative trend in population growth rate when density increased. Density-dependence models were favored for pup body size and mass growth. Abundance had a clear influence on body length at high population-density, pups grew slower and were smaller at weaning than pups born in years with low population density. Abundance partly explained pup body mass variation and a weak effect was detected on pre-weaning survival. The causal mechanisms may be increased competition for food resources between breeding females, leading to a reduction of maternal input to their pups. Our results suggested that pup favored survival over growth and the development of their diving abilities in order to withstand the extreme fasting periods that are characteristic of this fur seal population. This analysis provides significant insight of density-dependent processes on early-life demographic parameters of a long lived and top-predator species, and more specifically on the pre-weaning stage with important consequences for our understanding of individual long-term fitness and population dynamics.     

Two behavioural traits promote fine-scale species segregation and moderate hybridisation in a recovering sympatric fur seal population

Background  

In systems where two or more species experience secondary contact, behavioural factors that regulate interspecific gene flow may be important for maintaining species boundaries and reducing the incidence of hybridisation. At subantarctic Macquarie Island, two species of fur seal breed in close proximity to one another, hybridise at very high levels (up to 21% of hybrid pups are born annually), yet retain discrete gene pools. Using spatial and genetic information collected for pups and adults over twelve years, we assessed two behavioural traits - inter-annual site fidelity and differences in habitat use between the species - as possible contributors to the maintenance of this species segregation. Further, we explored the breakdown of these traits in pure-species individuals and hybrids.     

Energy reserve utilization in northern elephant seal (<Emphasis Type="Italic">Mirounga angustirostris</Emphasis>) pups during the postweaning fast: size does matter

During fasting most mammals preferentially utilize lipid reserves for energy while sparing protein reserves. This presents a potential problem for marine mammals that also depend on lipids as a major component of blubber, the primary thermoregulatory structure. Because of this dual function for lipid, rates of lipid and protein utilization should be closely regulated during the postweaning fast in northern elephant seals (Mirounga angustirostris). To quantify energy expenditure during the fast, we measured body mass and composition of 60 pups at 2.3+/-0.2 days and 55.9+/-0.3 days postweaning in 1999 and in 2000. Body condition differed significantly between years. At weaning, body mass (125.9+/-3.8 kg) and percentage lipid content (39.3+/-0.6% of body mass) in 2000 were significantly greater than body mass (115.2+/-3.1 kg) and percentage lipid content (35.8+/-0.6%) in 1999. In general, percentage lipid content increased with body mass, and fatter pups utilized lipid at relatively higher rates during the fast. Lipid fueled 85-95% and 88-98% of energy expended by pups in 1999 and 2000, respectively. Postweaning fast duration (32-78 days) was positively correlated with body mass and hence lipid content at weaning. This suggests that body composition at weaning influences lipid utilization patterns and ultimately the duration of the postweaning fast in northern elephant seal pups.     

Postweaning duration and body composition changes in Southern elephant seal (Mirounga leonina) pups at King George Island.

Weaning mass in southern elephant seals is highly variable, the heaviest pups being three times as heavy as the lightest ones. After weaning, pups undergo an extensive postweaning period in which they draw on their reserves. To quantify the energy expenditure during the postweaning period, changes in mass, body composition, and postweaning duration were measured in southern elephant seals at King George Island, South Shetland Islands, Antarctica. Overall, mean pup weaning mass was 154 +/- 26 kg (n=117) and did not differ between sexes. Mean minimum postweaning duration was 42.5 +/- 7.5 d. Heavier animals at weaning had lower mass-specific mass loss rates than lighter ones, and a faster depletion of body reserves was associated with a shorter postweaning period. The proportion of body mass represented by fat at weaning was 37% +/- 4% (n=47) and did not differ between sexes. Of these pups, 36 were recaptured after a mean period of 36 d after weaning. On average, total mass loss measured in these animals (39 kg) was composed of 39% water, 47% fat, and 12% protein. The composition of mass loss was not significantly different between sexes and was not related to weaning mass or total body energy reserves. However, fatter animals at weaning lost more fat per kilogram lost than thinner ones. Late in the fast, males and females appeared to be in a similar body condition. Nevertheless, the overall proportion of body mass represented by fat at this time was lower than that presented by the same animals at weaning. We estimated that during the postweaning period pups lost, on average, 30% of their mass at weaning. This comprised approximately 35% of the energy and 32% of the fat in the pup's body.     

Protein catabolism in suckling and fasting northern elephant seal pups (Mirounga angustirostris)

Nursing elephant seal pups are hypothesized to be preadapted to the postweaning fast, yet no comparison of lipid or protein use for meeting metabolic costs has been made between these contrasting nutritional periods. To address this, protein catabolism was estimated in five elephant seal pups from measurements of urea turnover made twice during nursing and twice during the postweaning fast. Changes in body composition were measured in ten separate weaned pups via tritiated water dilution and matched to fasting urea turnover measurements in order to assess errors in protein catabolism derived from urea turnover rates. Estimates of lean mass loss based upon urea turnover and tritiated water dilution were in general agreement, supporting estimates of protein catabolism derived from urea turnover measurements. Protein catabolism was estimated to contribute less than 4% to the average metabolic rate of suckling and fasting pups implying strict protein conservation during both periods and supporting the shypothesis that suckling pups are pre-adapted to fasting. It is proposed that strict protein conservation across suckling and fasting compensates for relative reductions in maternal investment associated with the abbreviated lactation period of the elephant seal.     

Age, sex, and reproductive state influence free amino acid concentrations in the fasting elephant seal

Long-term fasting is a component of northern elephant seal (Mirounga angustirostris) life history requiring physiological adaptations to nitrogen conservation. Plasma free amino acids (FAAs) were determined for five elephant seal pups during the second and eighth weeks of the postweaning fast, six lactating female seals at 4-6 and 25 d postpartum, and seven sexually competitive adult male seals taken midway through the breeding season. Total FAAs declined in lactating females (11%) and pups (30%) with time fasting, but cystine concentration more than doubled in pups while decreasing by approximately 43% in lactating females. Methionine concentration significantly increased (approximately 68%) across lactation in adult females but was low for all classes of seal. Alanine was the most abundant FAA in adult males, and glycine became the dominant FAA in adult females late in lactation. Glutamine dominated the FAAs of weaned pups across the fast. Reductions in total FAAs of weanlings mirrored reductions in protein catabolism, but reductions in total FAAs also occurred in lactating females concomitant with an increase in protein catabolism. Observed variation in FAA concentrations may reflect ontogenetic requirements for certain amino acids in fasting weanlings. Similarly, increases in specific FAA concentrations across lactation may reflect variations in FAA flux resulting from the nutrient demands of lactogenesis.     

Ecological implications of body composition and thermal capabilities in young antarctic fur seals (Arctocephalus gazella)

In comparison with other homeotherms, young recently weaned marine mammals in high latitudes face exceptional energetic demands when foraging and thermoregulating. Lipids are an important source of energy and a major component of insulation that allows them to meet these demands. To examine the role of lipid stores in a high-latitude pinniped, we measured the body composition and thermoregulatory capabilities of Antarctic fur seal (Arctocephalus gazella) pups and yearlings by using flow-through respirometry and hydrogen isotope dilution. From these data, we constructed a model to examine the importance of postweaning fasting capability in free-ranging young fur seals. Resting metabolic rates were different for pups and yearlings measured in 0.6 degrees C water, 10.3 degrees C water, and ambient air; however, mass and percent lipid as covariates accounted for the different metabolic responses in pups and yearlings for all treatments. The estimated lower critical temperature for combined pups and yearlings was 14.4 degrees C, 10 degrees -15 degrees C above water temperatures normally experienced by Antarctic fur seals. Modeling predicted that a weaned fur seal pup would survive at sea from 9.8 to 36.2 d before succumbing to starvation. The most likely maximum travel distance within this time constraint suggests that food resources close to the natal rookery are important to first-year survival for this species.     

PUP PRODUCTION AND POPULATION TRENDS OF THE AUSTRALIAN FUR SEAL (ARCTOCEPHALUS PUSILLUS DORIFERUS)

We estimated the number of live Australian fur seal pups using capture-markresights, direct ground counts, or aerial photography at all breeding sites following the pupping season of November-December 2002. Pups were recorded at 17 locations; nine previously known colony sites, one newly recognized colony and seven haul-out sites where pups are occasionally born. In order of size, the colonies were Lady Julia Percy Island (5,899 pups), Seal Rocks (4,882), The Skerries (2,486), Judgment Rocks (2,427), Kanowna Island (2,301), Moriarty Rocks (1,007), Reid Rocks (384), West Moncoeur Island (257), and Tenth Island (124). The newly recognized site was Rag Island, in the Cliffy Group, where we recorded 30 pups. We also recorded pups at the following haul-out sites: Cape Bridge-water (7 pups), Bull Rock (7), Wright Rock (5), Twin Islet (1), The Friars (1), He des Phoques (1), and Montague Island (1). In total, we estimate there were 19,819 (SE = 163) live pups at the time of the counts. We discuss trends in pup numbers and derive current population estimates for the Australian fur seal.     

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.     

Salmonellae in feral pinnipeds off the Southern California coast

Rectal swabs were collected from 90 Northern fur seal (Callorhinus ursinus) and 50 California sea lion (Zalophus californianus) pups on San Miguel Island for Salmonella screening. Three serotypes (newport, heidelberg, and oranienburg) were recovered from 33% of the fur seals and 40% of the sea lions.     

Body condition at weaning affects the duration of the postweaning fast in gray seal pups (Halichoerus grypus)

Gray seals (Halichoerus grypus) undergo a terrestrial postweaning fast (PWF) that depletes energy reserves acquired during the suckling interval. Plasticity in PWF duration may ensure that pups of variable body condition depart for sea with adequate energy reserves. To test this hypothesis, we examined body condition of 30 gray seal pups at weaning and monitored their PWF duration. On average, fat accounted for 47.3% +/- 0.7% of their 53.2 +/- 1.3-kg weaning mass. Although fasting duration averaged 21 +/- 1.1 d (n = p28), there was considerable variation in fasting duration (9 to > 31 d) and the resulting age when pups departed to sea (26 to > 49 d). Percent fat at weaning(38.6%-54.6%) was positively correlated with fasting duration(n = 28, r = 0.376, P = 0.0489). In contrast, total body gross energy (735.3-1,447.4 MJ) and body mass (39.0-66.0 kg) were not correlated with fasting duration. Thus, body composition,not overall body reserves, predicted fasting duration, but the effect was weak, indicating that other factors also account for the observed variation in fasting duration. We speculate that pups with greater percent fat more effectively utilized lipid and conserved protein while meeting metabolic costs throughout the PWF. As a result, fatter pups extended the PWF duration,which may be critical for development of diving physiology and may have facilitated their survivorship to age 1.     

Distribution of post-weaning Antarctic fur seal Arctocephalus gazella pups at South Georgia

Potentially some of the biggest gaps in our knowledge about the ecology of Antarctic fur seals (Arctocephalus gazella) relate to juvenile animals. We investigated the at-sea distribution of five male and five female fur seal pups post-weaning. The study was carried out at Bird Island, South Georgia during two successive winters using satellite-linked platform transmitter terminals (PTTs). Our results are analysed in relation to pup sex and the physical environment and productivity of those 2 years, as well as in the context of our present knowledge of where post-breeding females and males forage. The available physical and biological data during both of the winters of this study suggest that both years were not unusual. We report marked differences between the sexes with male pups foraging significantly further away from land and their birth site than do females. The pups foraged in areas to the East of Bird Island seldom reported as foraging areas for the adult population. Also as winter progressed they showed a more oceanic distribution leaving the continental shelf, possibly to exploit a different prey source that was more readily available in the upper water column.