Seasonal variability in whale encounters in the Western Antarctic Peninsula

Cetacean sighting surveys were conducted as part of nine multidisciplinary research cruises over late summer, autumn and winter of 2 years (2001–2003) during the Southern Ocean Global Ocean Ecosystems (SO GLOBEC) program. Sea-ice cover differed markedly between years, with apparent effects on cetacean distribution. No ice was present until late June in 2001, while the previous winter sea ice never fully retreated (>30% cover) during the 2002 or 2003 summer, thus increasing the proportion of thicker and more complex ice, including multi-year floes. Humpback (237 sightings; 537 individuals) and minke (103 sightings: 267 individuals) whales were the most commonly detected species. Data from seven comparable cruises were used to identify habitat for minke and humpback whales over five geographically distinct spatial divisions in the study area. In all years, both species were predominantly found in near coastal habitat, particularly in the fjords where complex habitat likely concentrated prey. In 2002 and 2003 the presence of sea ice provided additional feeding habitat, and the numbers of minkes (in winter) and humpbacks (late summer and autumn) in the area doubled compared with 2001. Humpbacks in particular were concentrated at the ice boundaries during late summer and autumn, while minke numbers increased in the winter that followed and occupied ice-covered areas along the entire shelf edge. Important resource sites for these species are mainly located in near-coastal areas and are used in all years, but when ice margins exist and intersect with resource sites they attract much larger numbers of animals due to the dynamics between sea ice and prey.

Description of loxocythere (novoloxocythere) pelius subgen. sp. nov. (ostracoda) from the cenozoic of S.E. Australia with comments on species of antarctiloxoconcha hartmann, 1986 and loxoreticulatum benson, 1964 from Australian and Antarctic marine waters

Loxocythere (Novoloxocythere) pelius subgen. et sp. nov. is described from Upper Miocene strata of the Port Phillip and Western Port Basins. Victoria. It has its acme in shallow open marine facies of latest Miocene (Cheltenhamian) age. This species, along with Loxocythere (Novoloxocythere) kerryswansoni Yassini and Jones, 1995, forms a discrete group of rotund Australian Loxocythere species that possess posterior extremities in both valves that are positioned well above mid carapace height (i.e. adjacent to dorsal margin). This feature along with a sub-triangular inner margin outline, defines a carapace shape that is distinct from that of rotund species of Loxocythere (loxocythere) Hornibrook, 1952 and Antarctiloxoconcha Hartmann, 1986. The type species of Antarctiloxoconcha – A.frigida (Neale. 1967), possesses internal carapace features that are very similar to the type species of Loxocythere - L. crassa Hornibrook, 1952. Both have relatively short carapaces and sub-quadrate inner margin outlines with posterior extremities in both valves positioned below mid carapace height. Species of Loxocythere (Novoloxocythere), in particular L. (N.) kerryswansoni, have a carapace shape that is transitional between Loxocythere and Loxoreticulatum Benson, 1964. Species of Loxoreticulatum generally possess a sub-parallelogram shaped carapace/inner margin and arched median hinge element. The latter feature is distinct from the mostly straight median hinge elements of Loxocythere (Loxocythere) and Loxocythere (Novoloxocythere) species. Species of Loxocythere (Novoloxocythere) are also readily distinguishable from relatively elongate species of Loxocythere, such as L. (L.) hornibrooki McKenzie, 1967, as the latter possess long (for genus), sub-rectangular shaped carapaces/inner margin outlines and posterior extremities below mid height.

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.

Whale distribution in relation to prey abundance and oceanographic processes in the shelf waters of the Western Antarctic Peninsula

The Western Antarctic Peninsula (WAP) is a biologically rich area supporting large standing stocks of krill and top predators (including whales, seals and seabirds). Physical forcing greatly affects productivity, recruitment, survival and distribution of krill in this area. In turn, such interactions are likely to affect the distribution of baleen whales. The Southern Ocean GLOBEC research program aims to explore the relationships and interactions between the environment, krill and predators around Marguerite Bay (WAP) in autumn 2001 and 2002. Bathymetric and environmental variables including acoustic backscattering as an indicator of prey abundance were used to model whale distribution patterns. We used an iterative approach employing (1) classification and regression tree (CART) models to identify oceanographic and ecological variables contributing to variability in humpback Megaptera novaeangliae and minke Balaenoptera acutorstrata whale distribution, and (2) generalized additive models (GAMs) to elucidate functional ecological relationships between these variables and whale distribution. The CART models indicated that the cetacean distribution was tightly coupled with zooplankton acoustic volume backscatter in the upper (25 to 100 m), and middle (100 to 300 m) portions of the water column. Whale distribution was also related to distance from the ice edge and bathymetric slope. The GAMs indicated a persistent, strong, positive relationship between increasing zooplankton volume and whale relative abundance. Furthermore, there was a lower limit for averaged acoustic volume backscatter of zooplankton below which the relationship between whales and prey was not significant. The GAMs also supported an annual relationship between whale distribution, distance from the ice edge and bathymetric slope, suggesting that these are important features for aggregating prey. Our results demonstrate that during the 2 yr study, whales were consistently and predictably associated with the distribution of zooplankton. Thus, humpback and minke whales may be able to locate physical features and oceanographic processes that enhance prey aggregation.

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

Seasonality of blue and fin whale calls and the influence of sea ice in the Western Antarctic Peninsula

The calling seasonality of blue (Balaenoptera musculus) and fin (B. physalus) whales was assessed using acoustic data recorded on seven autonomous acoustic recording packages (ARPs) deployed from March 2001 to February 2003 in the Western Antarctic Peninsula. Automatic detection and acoustic power analysis methods were used for determining presence and absence of whale calls. Blue whale calls were detected year round, on average 177 days per year, with peak calling in March and April, and a secondary peak in October and November. Lowest calling rates occurred between June and September, and in December. Fin whale calling rates were seasonal with calls detected between February and June (on average 51 days/year), and peak calling in May. Sea ice formed a month later and retreated a month earlier in 2001 than in 2002 over all recording sites. During the entire deployment period, detected calls of both species of whales showed negative correlation with sea ice concentrations at all sites, suggesting an absence of blue and fin whales in areas covered with sea ice. A conservative density estimate of calling whales from the acoustic data yields 0.43 calling blue whales per 1000 n mi² and 1.30 calling fin whales per 1000 n mi², which is about one-third higher than the density of blue whales and approximately equal to the density of fin whales estimated from the visual surveys.

Variation in maternal provisioning by lactating Antarctic fur seals: response to experimental manipulation in pup demand

An experiment involving the supplementary feeding of pups was conducted on Antarctic fur seals to investigate the factors influencing maternal foraging-attendance cycles and the differential use of nutritional resources for growth, maintenance and storage by pups. For 40% of the lactation period, male pups were given a supplement mimicking the chemical composition of Antarctic fur seal milk at a dose equivalent to 35% of the normal mass-specific milk energy intake for the species. Milk consumption, body composition and growth rates were monitored during and after the supplementary feeding period and maternal foraging-attendance cycles were monitored throughout lactation. During the supplementary feeding period, treatment pups (n=8) grew 32% faster and deposited greater adipose tissue stores than controls (n=8) but consumed the same amount of maternal-delivered milk. When supplementary feeding was stopped (timed to coincide with peak maternal milk yield in this species), treatment pups lost mass whereas control group pups continued to grow. Treatment pups weaned at a younger age (109 days) than control pups (116 days) but at the same mass (13 kg). Maternal attendance durations did not differ between the treatment and control groups throughout lactation. However, mothers of treatment pups had significantly shorter foraging trip durations (3.74 days) than mothers of control pups (4.74 days) during the period of supplementary feeding (there were no significant differences throughout the rest of lactation). These findings are in accordance with predictions of a marginal-value model of fur seal lactation behaviour.

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·ml^-1 in lactating females and 1.79-4.80 ng·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.

Fasting metbabolism in Antarctic fur seal (Artocephalus 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 (F₁,₁₈=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.

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.

Histological alterations in the Antarctic cod, Trematomus bernacchii from Davis Station, East Antarctica

During the summer season 2009/10, a comprehensive environmental impact assessment of the sewage discharge was conducted at Davis Station in the Vestfold Hills region of East Antarctica. As part of this project, a survey of the histology of liver, gill, gonad and muscle tissues in the Antarctic rock cod Trematomus bernacchii from nearshore sites in the receiving environment close to Davis Station in was completed. Fish from 4 sites were examined; 1 site adjacent to the Davis Station sewage outfall (within 500 m of the point of discharge), 2 sites approximately 2 km from the outfall (Anchorage Island and Antennae farm), and 1 site approximately 10 km away from the outfall and adjacent to an Adelie penguin population (Kazak Island). All fish sampled from the sewage outfall site exhibited significant histological alterations in all major tissues. Fish from the other 3 sites showed some alterations in either gill and/or liver tissues. Pathological abnormalities present in all fish collected near the sewage outfall included: extensive multifocal cysts of unknown etiology with necrotic liquification; multifocal granuloma with associated inflammation; coagulative necrosis in the liver; and lamellar hyperplasia with associated proliferation and lamella fusion of the gills. Results of this work form part of a weight of evidence approach alongside ecological monitoring, chemical analysis, ecotoxicological testing and dispersal modelling of the discharge plume which is being used to inform and direct upgrades to the Australian Antarctic Divisions operations and current sewage discharge practises at Davis Station.

Gene flow in east antarctic echinoderms and resilience to climate change

The spatial scales of population genetic structure in three species of Antarctic echinoderm, Sterechinus neumayeri, Abatus nimrodi and Abatus ingens was quantified using mitochondrial sequences and a novel set of microsatellite markers. Reduced fertilisation success in S. neumayeri resulting from increasing temperature and decreasing salinity was also identified.