Influence of maternal mass and condition on energy transfer in Weddell seals

1. Environmental variation influences food abundance and availability, which is reflected in the reproductive success of top predators. We examined maternal expenditure, offspring mass and condition for Weddell seals in 2 years when individuals exhibited marked differences in these traits. 2. For females weighing > or = 355 kg there was a positive relationship between maternal post-partum mass (MPPM) and lactation length, but below this there was no relationship, suggesting that heavier females were able to increase lactation length but lighter females were restricted to a minimum lactation period of 33 days. 3. Overall, females were heavier in 2002, but in 2003 shorter females were lighter than similar-sized females in 2002 suggesting that the effects of environmental variability on foraging success and condition are more pronounced in smaller individuals. 4. There was no relationship between MPPM and pup birth mass, indicating pre-partum investment did not differ between years. However, there was a positive relationship between MPPM and pup mass gain. Mass and energy transfer efficiency were 10.2 and 5.4% higher in 2002 than 2003, which suggests costs associated with a putatively poor-resource year were delayed until lactation. 5. Heavier females lost a higher proportion of mass during lactation in both years, so smaller females may not have been able to provide more to their offspring to wean a pup of similar size to larger females. 6. MPPM had only a small influence on total body lipid; therefore, regardless of mass, females had the same relative body composition. Females with male pups lost a higher percentage of lipid than those with female pups, but by the end of lactation female pups had 4.5% higher lipid content than males. 7. It appears that for Weddell seals the consequences of environmentally induced variation in food availability are manifested in differences in maternal mass and expenditure during lactation. These differences translate to changes in pup mass and condition at weaning with potential consequences for future survival and recruitment.     

Spatial variation in age-specific probabilities of first reproduction for Weddell seals

Spatial variation in vital rates can affect the dynamics and persistence of a population. We evaluated the prediction that age-specific probabilities of survival and first reproduction for Weddell seals would vary as a function of birth location in Erebus Bay, Antarctica. We used multi-state mark–resight models and 25 years of data to estimate demographic rates for female seals. We predicted that probabilities of survival and first reproduction would be higher for seals born at near-shore colonies or more southerly-located colonies with consistent ice conditions. Contrary to predictions, results revealed higher age-specific probabilities of first reproduction at offshore colonies relative to near-shore colonies and no spatial variation in survival rates. For 7-year old females (average age at 1st reproduction=7.6 years old) born at offshore colonies to mothers aged 10.8 years (average maternal age), probability of first reproduction was 0.43 (SE=0.07), whereas probability of first reproduction for females born at near-shore colonies was 0.30 (SE=0.05) based on estimates from our top-ranked model. Breeding probabilities following first reproduction were also higher at offshore colonies. Thus, our results (1) provide evidence of spatial variation in breeding probabilities, (2) reveal the importance of birth location on a female's vital rates, and (3) suggest that the effect persisted for many years. Birth-colony effects may be attributed to spatial variation in prey availability, or to heterogeneity in female quality in this population. If females who are superior competitors consistently chose offshore colonies for pupping, pups born at these locations may have inherited those superior qualities and displayed higher probabilities of first reproduction, relative to seals born at other colonies. Further research into physical or food-related differences among colonies may offer insight into spatial variation in breeding probabilities documented in this paper.     

Effects of pup age,maternal age,and birth date on pre‐weaning survival rates of Weddell seals in Erebus Bay,Antarctica

Identifying factors affecting juvenile survival is important to understanding the dynamics of populations and may also provide insights into life history theory and the selective forces shaping evolution. Quantifying the relative influence of the various potential selective forces for the post‐birth, maternal dependency, and independent periods is difficult and often limits investigators to estimating a single juvenile survival rate for the first year of life, or from birth to recruitment. We examined survival of individually marked Weddell seal Leptonychotes weddellii pups during the maternal dependency period in Erebus Bay, Antarctica from 2005–2007. We used mark‐recapture models to evaluate competing a priori hypotheses regarding variation in daily pre‐weaning survival rates (φ) during the first 42 days of age. The a priori model receiving the most support from the data supported several of our predictions: increased with pup age and was higher for pups born later in the season and to older mothers. Increases in with increasing pup age may have been due to improved resilience to the environment, phenotypic selection against the frailest pups, or both. Maternal age was more important to than was maternal experience or age of primiparity, potentially indicating that age‐related increases in body mass allow greater offspring provisioning, or age‐related improvements in competitive abilities benefit offspring during the period of maternal care. Depending on the timing of birth and the age of the mother, ^{42 days} ranged from 0.79 (SE = 0.05) to 0.98 (SE = 0.01). These exceptionally high pre‐weaning survival rates contrast with estimates from other large terrestrial and marine mammal species where neonate survival is considerably lower and suggest that in species with similar life histories, pre‐weaning survival probability may be buffered from both predators and environmental fluctuations during the period of maternal nutritional dependency. Climatic changes affecting stability of ice used for pupping substrate or extent of fast‐ice buffering pupping colonies from predators have the potential to reduce pre‐weaning survival and may have important implications for population growth rates.     

Blood rheology of Weddell seals and bowhead whales

Red blood cell (RBC) aggregation and blood viscosity are important determinants of in vivo blood flow dynamics and, in marine mammals, these parameters may impact diving physiology by altering blood oxygen delivery during the diving response. Weddell seals are superb divers and exhibit age-related patterns in blood oxygen chemistry and diving ability. By contrast, bowhead whales are not long duration divers, and little is known of their blood properties relative to diving. The present study was designed to compare rheological characteristics of blood from Weddell seal pups, Weddell seal adults, and from adult bowhead whales: blood viscosity and RBC aggregation in plasma and in polymer solutions (i.e., RBC "aggregability") were measured. Salient findings included: (1) significant 4- to 8-fold greater aggregation in blood from adult seals compared with pups and human subjects; (2) 2-to 8-fold greater aggregation in bowhead whale blood compared with human blood; (3) compared to human red cells, enhanced RBC aggregability of RBC from adult seals and whales as determined by their greater aggregation in polymer solutions; (4) increasing RBC aggregation and aggregability of seal pup blood over a seven day period following birth; (5) significantly greater blood viscosity for adult seals compared with pups at both native and standardized hematocrits. These results indicate that, for both species, hemorheological parameters differ markedly from those of humans, and suggest progressive changes with seal age; the physiological implications of these differences have yet to be fully defined.     

Three-dimensional dive profiles of free-ranging Weddell seals

We used an acoustic tracking system to record under-ice movements of two free-ranging adult male Weddell seals. The two males were unconstrained and interacting with other Weddell seals at a breeding colony in McMurdo Sound, Antarctica. We reconstructed three-dimensional paths of 279 dives by these seals. All dives were less than 20-min duration and none were deeper than 220 m. These three-dimensional dive profiles were compared with conventional time-depth dive profiles recorded using microprocessor loggers. We assigned each of the 279 dives to 1 of 6 classes using an existing classification scheme on the basis of the time-depth trace. Within these, two-dimensionally derived, classes the actual three-dimensional dive profiles at times varied profoundly. Additional parameters obtained with the acoustic system, such as bearing and distance travelled between diving and surfacing points, demonstrate that significant, additional, biologically important information can be derived from the three-dimensional data. Accepted: 19 December 1999     

Serum chemistry and antibodies against pathogens in antarctic fur seals, Weddell seals, crabeater seals, and Ross seals

Information on health parameters, such as antibody prevalences and serum chemistry that can reveal exposure to pathogens, disease, and abnormal physiologic conditions, is scarce for Antarctic seal species. Serum samples from Antarctic fur seals (Arctocephalus gazella, n=88) from Bouvet?ya (2000-2001 and 2001-2002), and from Weddell seals (Leptonychotes weddellii, n=20), Ross seals (Ommatophoca rossii, n=20), and crabeater seals (Lobodon carcinophagus, n=9) from the pack-ice off Queen Maud Land, Antarctica (2001) were analyzed for enzyme activity, and concentrations of protein, metabolites, minerals, and cortisol. Adult Antarctic fur seal males had elevated levels of total protein (range 64-99 g/l) compared to adult females and pups (range 52-79 g/l). Antarctic fur seals had higher enzyme activities of creatine kinase, lactate dehydrogenase, and amylase, compared to Weddell, Ross, and crabeater seals. Antibodies against Brucella spp. were detected in Weddell seals (37%), Ross seals (5%), and crabeater seals (11%), but not in Antarctic fur seals. Antibodies against phocine herpesvirus 1 were detected in all species examined (Antarctic fur seals, 58%; Weddell seals, 100%; Ross seals, 15%; and crabeater seals, 44%). No antibodies against Trichinella spp., Toxoplasma, or phocine distemper virus (PDV) were detected (Antarctic fur seals were not tested for PDV antibodies). Antarctic seals are challenged by reduced sea ice and increasing temperatures due to climate change, and increased anthropogenic activity can introduce new pathogens to these vulnerable ecosystems and represent a threat for these animals. Our data provide a baseline for future monitoring of health parameters of these Antarctic seal species, for tracking the impact of environmental, climatic, and anthropogenic changes in Antarctica over time.     

Successful foraging zones of southern elephant seals from the Kerguelen Islands in relation to oceanographic conditions

Southern elephant seals, Mirounga leonina, undertake large-scale oceanic movements to access favourable foraging areas. Successful foraging areas of elephant seals from the Kerguelen Islands are investigated here in relation to oceanographic parameters. Movements and diving activity of the seals as well as oceanographic data were collected through a new generation of satellite relayed devices measuring and transmitting locations, pressure, temperature and salinity. For the first time, we have associated foraging behaviour, determined by high increased sinuosity in tracks, and dive density (i.e. number of dives performed per kilometre covered), and changes in body condition, determined by variations in drift rate obtained from drift dives, to identify the oceanographic conditions of successful foraging zones for this species. Two main sectors, one close to the Antarctic continent and the other along the Polar Front (PF), where both foraging activity and body condition increase, seem to be of particular interest for the seals. Within these regions, some seals tended to focus their foraging activity on zones with particular temperature signatures. Along the Antarctic continent, some seals targeted colder waters on the sea bottom during benthic dives, while at the PF the favourable zones tended to be warmer. The possible negative effect of colder waters in Antarctic on the swimming performances of potential fish or squid prey could explain the behaviour of elephant seals in these zones, while warmer waters within the PF could correspond to the optimal conditions for potential myctophid prey of elephant seals.     

A safe and practical inhalation anaesthesia for Weddell seals

Nine adult female Weddell seals were anaesthetized during the breeding season using the inhalation anaesthetic sevoflurane. The seals were captured with a head bag. Sevoflurane was administered and vaporized into the bag. A dose of 5 ml sevoflurane induced narcosis 1 min after application. Anaesthesia was maintained by multiple follow-up doses of 2 ml at an interval of 2 min. The average duration for complete recovery was 11Dž min after the terminal application. Sevoflurane is a reliable volatile anaesthetic that requires a minimum of equipment even under the low temperature regime of Antarctica.     

Variation in probability of first reproduction of Weddell seals

1. For many species, when to begin reproduction is an important life-history decision that varies by individual and can have substantial implications for lifetime reproductive success and fitness. 2. We estimated age-specific probabilities of first-time breeding and modelled variation in these rates to determine age at first reproduction and understand why it varies in a population of Weddell seals in Erebus Bay, Antarctica. We used multistate mark-recapture modelling methods and encounter histories of 4965 known-age female seals to test predictions about age-related variation in probability of first reproduction and the effects of annual variation, cohort and population density. 3. Mean age at first reproduction in this southerly located study population (7.62 years of age, SD=1.71) was greater than age at first reproduction for a Weddell seal population at a more northerly and typical latitude for breeding Weddell seals (mean=4-5 years of age). This difference suggests that age at first reproduction may be influenced by whether a population inhabits the core or periphery of its range. 4. Age at first reproduction varied from 4 to 14 years, but there was no age by which all seals recruited to the breeding population, suggesting that individual heterogeneity exists among females in this population. 5. In the best model, the probability of breeding for the first time varied by age and year, and the amount of annual variation varied with age (average variance ratio for age-specific rates=4.3%). 6. Our results affirmed the predictions of life-history theory that age at first reproduction in long-lived mammals will be sensitive to environmental variation. In terms of life-history evolution, this variability suggests that Weddell seals display flexibility in age at first reproduction in order to maximize reproductive output under varying environmental conditions. Future analyses will attempt to test predictions regarding relationships between environmental covariates and annual variation in age at first reproduction and evaluate the relationship between age at first reproduction and lifetime reproductive success.     

Immobilisation of free-living Weddell seals Leptonychotes weddellii using midazolam and isoflurane

Eleven lactating female Weddell seals were immobilised using inhaled isoflurane and oxygen, having initially been sedated using an intramuscular injection of midazolam. The seals were selected from colonies in Long Fjord, East Antarctica. Isoflurane was delivered using a precision, out-of-circle vaporiser in a portable, heated, semi-closed circle system anaesthetic machine. Induction time (time from injection of midazolam to detected maximal effect of midazolam) ranged from 12 min to 29 min. The maximal effect of midazolam was assessed as being either moderate sedation (n=9) or heavy sedation (n=2), and the maximal effect of inhaled isoflurane and oxygen was assessed as being light anaesthesia (n=11). The level of chemical restraint achieved using this combination allowed attachment of heart rate monitoring units and collection of biological samples. Recovery time ranged from 1 min to 11 min. The anaesthetic regime proved a practical, safe and reliable method for the immobilisation of lactating Weddell seals under conditions of low environmental temperature.     

Annual and diurnal variations in the underwater vocalizations of Weddell seals

Summary Weddell seal vocalizations were recorded once a fortnight throughout 1984 at a major pupping site near Davis, Antarctica. Few vocalizations were heard between January and June. The number of vocalizations recorded increased from July to a peak in November and early December during the breeding period and then fell off rapidly through December. The increase in the number of seal vocalizations was correlated with a build up in seal numbers but some of the increase may be explained by an increased rate of vocalization by males.     

Effects of capture stress on free-ranging, reproductively active male Weddell seals

Physiological stress responses to capture may be an indicator of welfare challenges induced by animal handling. Simultaneously, blood chemistry changes induced by stress responses may confound experimental design by interacting with the biological parameters being measured. Cortisol elevation is a common indicator of stress responses in mammals and reproductive condition can profoundly influence endocrine response. We measured changes in blood cortisol and testosterone induced by handling reproductively active male Weddell seals (Leptonychotes weddellii) early and late in the breeding season. Weddell seals have the highest resting cortisol levels of all mammals yet showed a clear, prolonged elevation in cortisol in response to capture. Responses were similar when first caught and when caught a second time, later in the breeding season. Baseline testosterone levels declined over the breeding season but were not altered by capture. Administering a light dose of diazepam significantly ameliorated the cortisol response of handled animals without affecting testosterone levels. This may be an effective way of reducing acute capture stress responses. Male breeding success in years males were handled was no different to the years they were not, despite the acute capture response, suggesting no long-term impact of handling on male reproductive output.     

Movements of adult female Weddell seals during the winter months

The focus of this study was the distribution of adult female Weddell seals during winter at the Vestfold Hills. Satellite tracking of Weddell seals had never been done before at this location. Hence, this was a pilot study to evaluate the following methods. We attached satellite transmitters to the lower back, where there was least potential to change the seals’ behaviour or to damage instruments on the ice. Location data were obtained only where the seals hauled out, not necessarily where they were feeding. All locations were within the area of fast-ice that was associated with the Vestfold Hills. There were gaps of up to 30 days in the location data sets. Each instrument (n=3) remained attached and functioning for ca. 6 months. During that time, two of the three seals hauled out within small areas adjacent to, or nearby, open water. The same seals hauled out sporadically. We inferred that these seals foraged offshore whilst returning to fast-ice to rest. If Weddell seals forage beneath dynamic ice but return to stable ice as their preferred resting substrate, then evidence of haulout sites will always be a biased measure of foraging range. Tracking seals in the water may be possible using alternative placement of transmitters. However, there is potential for instruments to interfere with movement (breathing and prey capture). For this reason, we recommend a combination of sensors, diet and tracking haulout sites to research winter foraging.     

Linear oceanographic features: A focus for research on recruitment processes

The early life of reef-associated organisms is generally spent in the plankton. Recent evidence suggests that oceanographic processes have an important influence on the fate of early developmental forms; a surprising number of these manifest themselves as lines at the ocean surface. Lines, or slicks, are convergence zones where organic material collects. Internal waves, Langmuir circulations, topographically controlled fronts, estuarine, coastal and oceanic fronts produce linear or curvi-linear slicks. The biological importance of these features is discussed. Slicks are ideal for investigating factors influencing meroplankton.     

Spatial utilisation of fast-ice by Weddell seals Leptonychotes weddelli during winter

This study describes the distribution of Weddell seals Leptonychotes weddelli in winter (May–September 1999) at the Vestfold Hills, in Prydz Bay, East Antarctica. Specifically, we describe the spatial extent of haul-out sites in shore–fast sea-ice, commonly referred to as fast-ice. As winter progressed, and the fast-ice grew thick (ca 2 m), most of the inshore holes closed over, and the seals' distribution became restricted to ocean areas beyond land and islands. Using observations from the end of winter only, we fitted Generalised Additive Models (GAMs) to generate resource selection functions, which are models that yield values proportional to the probability of use. The models showed that seal distribution was defined mainly by distance to ice-edge and distance to land. Distance to ice-bergs was also selected for models of some regions. We present the results as maps of the fitted probability of seal presence, predicted by the binomial GAM for offshore regions, both with and without autocorrelation terms. The maps illustrate the expected distribution encompassing most of the observed distribution. On this basis, we hypothesise that propensity for the fast-ice to crack is the major determinant of Weddell seal distribution in winter. Proximity to open water and pack-ice habitats could also influence the distribution of haul-out sites in fast-ice areas. This is the first quantitative study of Weddell seal distribution in winter. Potential for regional variation is discussed.     

Evaluation of reproductive costs for Weddell seals in Erebus Bay, Antarctica

1. Organisms balance current reproduction against future survival and reproduction, which results in life-history trade-offs. These trade-offs are also known as reproductive costs and may represent significant factors shaping life-history strategy for many species. 2. Using multistate mark-resight models and 26 years of mark-resight data (1979-2004), we estimated the costs of reproduction to survival and reproductive probabilities for Weddell seals in Erebus Bay, Antarctica and evaluated whether this species either conformed to the 'prudent parent' reproductive strategy predicted by life-history theory for long-lived mammals or alternatively, incurred costs to survival in order to reproduce in a variable environment (flexible-strategy hypothesis). 3. Results strongly supported the presence of reproductive costs to survival (mean annual survival probability was 0.91 for breeders vs. 0.94 for nonbreeders), a notable difference for a long-lived mammal, demonstrating that investment in reproduction does result in a cost to survival for Weddell seals, contrary to the prudent parent hypothesis. 4. Reproductive costs to subsequent reproductive probabilities were also present for first-time breeders (mean probability of breeding the next year was 31.3% lower for first-time breeders than for experienced breeders), thus supporting our prediction of the influence of breeding experience. 5. We detected substantial annual variation in survival and breeding probabilities. Breeding probabilities were negatively influenced by summer sea-ice extent, whereas weak evidence suggested that survival probabilities were affected more by winter sea-ice extent, and the direction of this effect was negative. However, a model with annual variation unrelated to any of our climate or sea-ice covariates performed best, indicating that further study will be needed to determine the appropriate mechanism or combination of mechanisms underlying this annual variation.     

Parasite recruitment and oceanographic regime: evidence suggesting a relationship on a global scale

We here investigate the relationship between oceanographic processes and variability in parasite recruitment to host populations using existing data from host-parasite systems encountering differing hydrographic conditions. Combined epidemiological data obtained from both exploited fish and cephalopod populations indicate that variability in recruitment of parasite infracommunities tends to be associated with major current systems of the World's oceans. It appears that instability in water masses caused by physical perturbations (e.g. water mass convergence and turbulent mixing in upwelling systems) is associated with instability of trophic interactions over time, which in turn leads to a paucity of parasite communities in that area. The likely relationship between parasite recruitment and oceanographic regime should be extremely useful to the fishing industry and also as an indicator of ecosystem health.