The comparative energetics and growth strategies of sympatric Antarctic and subantarctic fur seal pups at Iles Crozet

The period of maternal dependence is a time during which mammalian infants must optimise both their growth and the development of behavioural skills in order to successfully meet the demands of independent living. The rate and duration of maternal provisioning, post-weaning food availability and climatic conditions are all factors likely to influence the growth strategies of infants. While numerous studies have documented differences in growth strategies at high taxonomic levels, few have investigated those of closely related species inhabiting similar environments. The present study examined the body composition, metabolism and indices of physiological development in pups of Antarctic fur seals (Arctocephalus gazella) and subantarctic fur seals (Arctocephalus tropicalis), congeneric species with different weaning ages (4 months and 10 months, respectively), during their overlap in lactation at a sympatric breeding site in the Iles Crozet. Body lipid reserves in pre-moult pups were significantly greater (t₂₈=2.73, P<0.01) in subantarctic (26%) than Antarctic fur seals (22%). Antarctic fur seal pups, however, had significantly higher (t₂₆=3.82, P<0.001) in-air resting metabolic rates (RMR; 17.1±0.6 ml O₂ kg^-1 min^-1) than subantarctic fur seal pups (14.1±0.5 ml O2 kg^-1 min^-1). While in-water standard metabolic rate (SMR; 22.9±2.5 ml O2 kg^-1 min^-1) was greater than in-air RMR for Antarctic fur seal pups (t₉=2.59, P<0.03), there were no significant differences between in-air RMR and in-water SMR for subantarctic fur seal pups (t₁₂=0.82, P>0.4), although this is unlikely to reflect a greater ability for pre-moult pups of the latter species to thermoregulate in water. Pup daily energy expenditure was also significantly greater (t₂₇=2.36, P<0.03) in Antarctic fur seals (638±33 kJ kg^-1 day^-1) than in subantarctic fur seals (533±33 kJ kg^-1 day^-1), which corroborates observations that pups of the former species spend considerably more time actively learning to swim and dive. Consistent with this observation is the finding that blood oxygen storage capacity was significantly greater (t₉=2.81, P<0.03) in Antarctic (11.5%) than subantarctic fur seal (8.9%) pups. These results suggest that, compared with subantarctic fur seals, Antarctic fur seal pups adopt a strategy of faster lean growth and physiological development, coupled with greater amounts of metabolically expensive behavioural activity, in order to acquire the necessary foraging skills in time for their younger weaning age.

Foraging behaviour of sympatric Antarctic and subantarctic fur seals: does their contrasting duration of lactation make a difference?

The duration of periods spent ashore versus foraging at sea, diving behaviour, and diet of lactating female Antarctic (Arctocephalus gazella, AFS) and subantarctic (A. tropicalis, SFS) fur seals were compared at Iles Crozet, where both species coexist. The large disparity in lactation duration (SFS: 10 months, AFS: 4 months), even under local sympatry, has led to the expectation that AFS should exhibit higher foraging effort or efficiency per unit time than SFS to allow them to wean their pups in a shorter period of time. Previous evidence, however, has not supported these expectations. In this study, the distribution of foraging trip durations revealed two types of trips: overnight (OFT, <1 day) and long (LFT, >1 day), in common with other results from Macquarie Island. However, diving behaviour differed significantly between foraging trip types, with greater diving effort in OFTs than in LFTs, and diving behaviour differed between fur seal species. OFTs were more frequent in SFS (48%) than in AFS (28%). SFS performed longer LFTs and maternal attendances than AFS, but spent a smaller proportion of their foraging cycle at sea (66.2 vs. 77.5%, respectively). SFS dove deeper and for longer periods than AFS, in both OFTs and LFTs, although indices of diving effort were similar between species. Diel variation in diving behaviour was lower among SFS, which foraged at greater depths during most of the night time available than AFS. The diving behaviour of AFS suggests they followed the nychthemeral migration of their prey more closely. Concomitant with the differences in diving behaviour, AFS and SFS fed on the same prey species, but in different proportions of three myctophid fish (Gymnoscopelus fraseri, G. piabilis, and G. nicholsi) that represented most of their diet. The estimated size of the most important fish consumed did not vary significantly between fur seal species, suggesting that the difference in dive depth was mostly a result of changes in the relative abundance of these myctophids. The energy content of these fish at Iles Crozet may thus influence the amount and quality of milk delivered to pups of each fur seal species. These results contrast with those found at other sites where both species coexist, and revealed a scale of variation in foraging behaviour which did not affect their effort while at sea, but that may be a major determinant of foraging efficiency and, consequently, maternal investment.

Ontogeny of body size and shape of Antarctic and subantarctic fur seals

Pre- and post-weaning functional demands on body size and shape of mammals are often in conflict, especially in species where weaning involves a change of habitat. Compared with long lactations, brief lactations are expected to be associated with fast rates of development and attainment of adult traits. We describe allometry and growth for several morphological traits in two closely related fur seal species with large differences in lactation duration at a sympatric site. Longitudinal data were collected from Antarctic (Arctocephalus gazella (Peters, 1875); 120 d lactation) and subantarctic (Arctocephalus tropicalis (Gray, 1872); 300 d lactation) fur seals. Body mass was similar in neonates of both species, but A. gazella neonates were longer, less voluminous, and had larger foreflippers. The species were similar in rate of preweaning growth in body mass, but growth rates of linear variables were faster for A. gazella pups. Consequently, neonatal differences in body shape increased over lactation, and A. gazella pups approached adult body shape faster than did A. tropicalis pups. Our results indicate that preweaning growth is associated with significant changes in body shape, involving the acquisition of a longer, more slender body with larger foreflippers in A. gazella. These differences suggest that A. gazella pups are physically more mature at approximately 100 d of age (close to weaning age) than A. tropicalis pups of the same age

Body composition changes, metabolic fuel use and energy expenditure during extended fasting in subantarctic fur seal (Arctocephalus tropicalis) pups at Amsterdam Island

The fasting metabolism of 71- to 235-d-old subantarctic fur seal (Arctocephalus tropicalis) pups from Amsterdam Island, southern Indian Ocean, was investigated during the long foraging trips of their mothers. Body lipid reserves were proportionally greater in female than male pups and higher in postmoult (37%) than premoult (10%) animals. The mass-specific rate of mass loss did not differ between the sexes but was lower than observed in other species. Daily mass loss was estimated to 56% fat, 10% protein, and 34% water. The rate of protein catabolism (15 g d⁻¹) was negatively related to the size of initial lipid stores and accounted for 9% (±1%) of total energy expenditure. However, body composition changes during the fast were not equal between the sexes, with females relying more on protein catabolism than males (11% and 5% of total energy expenditure, respectively). Energy expenditure (270 kJ kg⁻¹ d⁻¹) and metabolic water production (11.5 mL kg⁻¹ d⁻¹) rates are the lowest reported for an otariid species. These results suggest that subantarctic fur seal pups greatly reduce activity levels to lower energy expenditure in addition to adopting protein-sparing metabolic pathways in order to survive the extreme fasts they must endure on Amsterdam Island.

Temporal structure of diving behaviour in sympatric Antarctic and Subantarctic fur seals

Lactation is considerably briefer (4 vs. 10 mo) and daily pup energy expenditure higher in Antarctic (AFS) than in subantarctic fur seals (SFS), even in sympatric populations of both species, where their foraging locations and diets are similar. Therefore, lactational demands may be higher for AFS females. We investigated whether sympatric lactating AFS and SFS females differ in their physiological or behavioural diving capacities, and in the temporal structure of foraging behaviour. Mean dive depth and duration were greater in SFS, but dives below 140 m were performed only by AFS. An index of activity level during the bottom phase of dives, when fur seals are thought to capture prey, was higher in SFS. Despite these differences, SFS females showed a steady increase in the minimum postdive interval following dives lasting longer than 250 s, compared to the steady increase following dives lasting longer than only 150 s in AFS. These results suggest that physiological constraints on diving behaviour are stronger on AFS females, and that the behavioural aerobic dive limit is greater for SFS. Assuming that dive bouts reflect foraging in prey patches, AFS females exploited more patches per unit time, and remained in them for briefer periods of time, compared to SFS females. Dive bout structure did not differ between overnight and long foraging trips. Our data suggest that AFS females spend greater foraging effort, but may gain access to prey patches of better quality, which may help them cope with higher lactational demands.

Bathymetry and frontal system interactions influence seasonal foraging movements of lactating subantarctic fur seals from Marion Island

Sixteen lactating subantarctic fur seals Arctocephalus tropicalis were satellite-tracked during the winter of 2006 (n = 6), summer of 2006/07 (n = 6) and autumn/winter (n = 4) of 2007, from Marion Island, Southern Ocean. Despite varied individual movement patterns, a favoured foraging area lay to the northeast of the island. In contrast to findings for populations at similar latitudes, seals from Marion Island did not undertake short overnight foraging trips, but trips consistently went beyond 300 km from the island. This aligns with the at-sea duration of lactating seals’ foraging trips from temperate Amsterdam Island, but differs from subantarctic Crozet and Macquarie islands. Time spent at sea, maximum distances travelled and movement variation of tracks from the island varied seasonally. Faecal analysis suggests the diet comprised primarily myctophid fish with limited seasonal variation. Well-defined areas of restricted movement coincided with significant bathymetric features to the west/northwest of the Crozet Plateau, with the Del Caño Rise clearly being important. Positive and negative sea-surface height anomalies (compared to the mean) appeared to be preferred by most seals across seasons. Higher summer sea-surface temperatures correlated with the movements of some seals. Higher chlorophyll a concentrations dictated transit and foraging areas during summer. Bathymetrically influenced oceanographic variables likely explain these preferred long-distance eastward movements. The Îles Crozet and Marion island subantarctic fur seals differ in their foraging ecology despite being neighbours. Conversely, the subantarctic fur seal populations from the distant Amsterdam and Marion islands appear to be similarly influenced by such environmental factors.

Physiological response to extreme fasting in subantarctic fur seal (Arctocephalus tropicalis) pups : metabolic rates, energy reserve utilization, and water fluxes

Physiological response to extreme fasting in subantarctic fur seal (Arctocephalus tropicalis) pups: metabolic rates, energy reserve utilization, and water fluxes. Am J Physiol Regul Integr Comp Physiol 297: R1582–R1592, 2009. First published September 23, 2009; doi:10.1152/ajpregu.90857.2008.— Surviving prolonged fasting requires various metabolic adaptations, such as energy and protein sparing, notably when animals are simultaneously engaged in energy-demanding processes such as growth. Due to the intermittent pattern of maternal attendance, subantarctic fur seal pups have to repeatedly endure exceptionally long fasting episodes throughout the 10-mo rearing period while preparing for nutritional independence. Their metabolic responses to natural prolonged fasting (33.4 ± 3.3 days) were investigated at 7 mo of age. Within 4–6 fasting days, pups shifted into a stage of metabolic economy characterized by a minimal rate of body mass loss (0.7%/day) and decreased resting metabolic rate  (5.9 ± 0.1 ml O₂ ·kg^-1·day^-1) that was only 10% above the level predicted for adult terrestrial mammals. Field metabolic rate (289 ± 10 kJ·kg^-1 ·day^-1) and water influx (7.9 ± 0.9 ml·kg^-1 ·day^-1) were also among the lowest reported for any young otariid, suggesting minimized energy allocation to behavioral activity and thermoregulation. Furthermore, lean tissue degradation was dramatically reduced. High initial adiposity (>48%) and predominant reliance on lipid catabolism likely contributed to the exceptional degree of protein sparing attained. Blood chemistry supported these findings and suggested utilization of alternative fuels, such as β-hydroxybutyrate and de novo synthesized glucose from fat-released glycerol. Regardless of sex and body condition, pups tended to adopt a convergent strategy of extreme energy and lean body mass conservation that appears highly adaptive for it allows some tissue growth during the repeated episodes of prolonged fasting they experience throughout their development.

Hormonal responses to extreme fasting in subantarctic fur seal (Arctocephalus tropicalis) pups

Surviving prolonged fasting implies closely regulated alterations in fuel provisioning to meet metabolic requirements, while preserving homeostasis. Little is known, however, of the endocrine regulations governing such metabolic adaptations in naturally fasting free-ranging animals. The hormonal responses to natural prolonged fasting and how they correlate to the metabolic adaptations observed, were investigated in subantarctic fur seal (Arctocephalus tropicalis) pups, which, because of the intermittent pattern of maternal attendance, repeatedly endure exceptionally long fasting episodes throughout their development (1–3 mo). Phase I fasting was characterized by a dramatic decrease in plasma insulin, glucagon, leptin, and total L-thyroxine (T4) associated with reductions in mass-specific resting metabolic rate (RMR), plasma triglycerides, glycerol, and urea-to-creatine ratio, while nonesterified fatty acids (NEFA) and β-OHB increased. In contrast, the metabolic steady-state of phase II fasting reached within 6 days was associated with minimal concentrations of insulin, glucagon, and leptin; unchanged cortisol and triiodothyronine (T3); and moderately increased T4. The early fall in insulin and leptin may mediate the shift to the strategy of energy conservation, protein sparing, and primary reliance on body lipids observed in response to the cessation of feeding. In contrast to the typical mammalian starvation response, nonelevated cortisol and minimal glucagon levels may contribute to body protein preservation and downregulation of catabolic pathways, in general. Furthermore, thyroid hormones may be involved in a process of energy conservation, independent of pups' nutritional state. These original hormonal settings might reflect an adaptation to the otariid repeated fasting pattern and emphasize the crucial importance of a tight physiological control over metabolism to survive extreme energetic constraints.

Determinants of individual foraging specialization in large marine vertebrates, the Antarctic and subantarctic fur seals

The degree of individual specialization in resource use differs widely among wild populations where individuals range from fully generalized to highly specialized. This interindividual variation has profound implications in many ecological and evolutionary processes. A recent review proposed four main ecological causes of individual specialization: interspecific and intraspecific competition, ecological opportunity and predation. Using the isotopic signature of subsampled whiskers, we investigated to what degree three of these factors (interspecific and intraspecific competition and ecological opportunity) affect the population niche width and the level of individual foraging specialization in two fur seal species, the Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalus tropicalis), over several years. Population niche width was greater when the two seal species bred in allopatry (low interspecific competition) than in sympatry or when seals bred in high-density stabilized colonies (high intraspecific competition). In agreement with the niche variation hypothesis (NVH), higher population niche width was associated with higher interindividual niche variation. However, in contrast to the NVH, all Antarctic females increased their niche width during the interbreeding period when they had potential access to a wider diversity of foraging grounds and associated prey (high ecological opportunities), suggesting they all dispersed to a similar productive area. The degree of individual specialization varied among populations and within the annual cycle. Highest levels of interindividual variation were found in a context of lower interspecific or higher intraspecific competition. Contrasted results were found concerning the effect of ecological opportunity. Depending on seal species, females exhibited either a greater or lower degree of individual specialization during the interbreeding period, reflecting species-specific biological constraints during that period. These results suggest a significant impact of ecological interactions on the population niche width and degree of individual specialization. Such variation at the individual level may be an important factor in the species plasticity with significant consequences on how it may respond to environmental variability.

Seawater temperature effect on metal accumulation and toxicity in the subantarctic Macquarie Island isopod, Exosphaeroma gigas

Very little is currently known of subantarctic nearshore invertebrates' sensitivity to environmental metals and the role of temperature in this relationship. This study investigated Cu and Zn toxicity in the common subantarctic intertidal isopod, Exosphaeroma gigas, and the influence of temperature on Cu toxicity and bioaccumulation kinetics. Adult E. gigas are insensitive to Cu and Zn at concentrations of 3200 and 7400μg/L respectively in non-renewal tests at 5.5°C (ambient subtidal temperature) over 14days. Under renewed exposures over the same temperature and time period the LC50 for copper was 2204μg/L. A 10-fold increase in Cu body burden occurred relative to zinc, indicating E. gigas has different strategies for regulating the two metals. Copper toxicity and time to mortality both increased with elevated temperature. However, temperature did not significantly affect Cu uptake rate and efflux rate constants derived from biodynamic modelling at lower Cu concentrations. These results may be attributable to E. gigas being an intertidal species with physiological mechanisms adapted to fluctuating environmental conditions. Cu concentrations required to elicit a toxicity response indicates that E. gigas would not be directly threatened by current levels of Cu or Zn present in Macquarie Island intertidal habitats, with the associated elevated temperature fluctuations. This study provides evidence that the sensitivity of this subantarctic intertidal species to metal contaminants is not as high as expected, and which has significance for the derivation of relevant guidelines specific to this distinct subpolar region of the world.

Coastal state fisheries management : a review of Australian enforcement action in the Heard and McDonald Islands Australian Fishing Zone

In 1953 the Heard and McDonald Islands Act, which formalised the transfer of sovereignty over the two named sub-Antarctic islands from the United Kingdom, was passed by the Australian Government. For the ensuing 40 years, Australian management of the Islands was uneventful. The first subAntarctic scientific station was established at Atlas Cove, on Heard Island, in December 1947 following the initial indication by Britain of a willingness to transfer rights to the Islands. In 1987 the Islands, together with their 12 mile territorial sea, were proclaimed a wilderness reserve with a number of activities including fishing and mining prohibited. The same area was included on the WorId Heritage List in 1997. In 1979 a 200 nautical mile Australian Fishing Zone (AFZ) was proclaimed around all Australian territories. In 1994 new terminology was embraced and the Exclusive Economic Zone was declared.

Differences in foraging strategy and maternal behaviour between two sympatric fur seal species at the Crozet Islands

Marine top-predators such as marine mammals forage in a heterogeneous environment according to their energetic requirements and to the variation in environmental characteristics. In this study, the behaviour of breeding females in 2 sympatric fur seal species, Antarctic fur seal Arctocephalus gazella and Subantarctic fur seal A. tropicalis, was investigated in relation to foraging effort. Foraging effort was hypothesised to be greater in Antarctic fur seal than in Subantarctic fur seal due to their shorter lactation period. Using satellite telemetry, time-depth recorders and satellite images of sea-surface temperature and chlorophyll a concentration, the foraging grounds, the at-sea activity budgets and the environmental features were determined for both species breeding on the Crozet Archipelago. Foraging cycle duration was similar for the 2 species, and the seals exhibited similar at-sea activity budgets. Only the proportion of time spent at sea was higher in Antarctic fur seals. Separate foraging areas were identified for the 2 species. Antarctic fur seal distribution was related to bathymetric features, while we did not find any direct relationship between chlorophyll a concentration and seal foraging areas. Our results suggest that Antarctic fur seals tend to respond to the higher needs of their pups by having a higher foraging efficiency and concentrating their foraging activity in the most productive areas.

Diet of common diving-petrels (Pelecanoides Urinatrix Urinatrix) in Southeastern Australia during chick rearing

Unlike conspecifics in the subantarctic region, which typically begin breeding in mid-spring to summer, Common Diving-petrels Pelecanoides urinatrix urinatrix in southeastern Australia (towards the northern limit of the species' distribution) commence breeding mid winter. Knowledge of the foraging ecology of this species is crucial to understanding the factors that influence its timing of breeding in the region, yet there is currently little information available. Analysis of 43 stomachs of breeding adults, collected opportunistically after they were killed in a fire which burned through their colony, indicated that their diet was dominated by two taxa: a euphausiid Nyctiphanes australis which comprised 87% of the diet by number; and a hyperiid amphipod Themisto australis which constituted a further 12.5%. Mean lengths (±SE) of N. australis (n = 39) and T. australis (n = 41) were 12 mm (±0.3) and 5.2 mm (±0.2), respectively. The importance of N. australis in the diet of Common Diving-petrels is discussed in relation to their timing of breeding and the euphausiid's potential role in the Bass Strait pelagic ecosystem.