Early functional maturity of captive male northern elephant seals (Mirounga angustirostris)

A male northern elephant seal (Mirounga angustirostris) that was conceived in captivity was stillborn February 14, 1981, at Mystic Marinelife Aquarium in Mystic, Connecticut. Either of two males in the exhibit could have sired the pup. Both were only 3 yr at the time of conception.     

Assessment of gestation,lactation and fasting on stable isotope ratios in northern elephant seals (Mirounga angustirostris)

Effects of physiological processes such as gestation, lactation and nutritional stress on stable isotope ratios remain poorly understood. To determine their impact, we investigated these processes in simultaneously fasting and lactating northern elephant seals (Mirounga angustirostris). Stable carbon and nitrogen isotope values were measured in blood and milk of 10 mother-pup pairs on days 5 and 22 of lactation. As long- and short-term integrators of diet, blood cells and serum may reflect foraging data or energy reserves from late gestation and lactation, respectively. Limited changes in isotopic signatures of maternal blood over the lactating period were highlighted. Nitrogen isotope fractionation associated with mother-to-offspring transfer of nutrients was generated between mother and offspring during gestation and lactation. This fractionation was tissue and time-specific, it varied between early and late lactation from +0.6‰ to +1.3‰ in blood cells and from +1.1‰ to nonsignificant value in serum. Therefore, if pups appear to be good proxies to investigate the female trophic ecology especially for C sources, much more caution is required in using δ¹⁵N values. Further studies are also needed to better define the relative impact of fasting and lactation on the enrichment or depletion of isotopes in different tissues.     

Oxygen minimum zone: An important oceanographic habitat for deep‐diving northern elephant seals,Mirounga angustirostris

Little is known about the foraging behavior of top predators in the deep mesopelagic ocean. Elephant seals dive to the deep biota‐poor oxygen minimum zone (OMZ) (>800 m depth) despite high diving costs in terms of energy and time, but how they successfully forage in the OMZ remains largely unknown. Assessment of their feeding rate is the key to understanding their foraging behavior, but this has been challenging. Here, we assessed the feeding rate of 14 female northern elephant seals determined by jaw motion events (JME) and dive cycle time to examine how feeding rates varied with dive depth, particularly in the OMZ. We also obtained video footage from seal‐mounted videos to understand their feeding in the OMZ. While the diel vertical migration pattern was apparent for most depths of the JME, some very deep dives, beyond the normal diel depth ranges, occurred episodically during daylight hours. The midmesopelagic zone was the main foraging zone for all seals. Larger seals tended to show smaller numbers of JME and lower feeding rates than smaller seals during migration, suggesting that larger seals tended to feed on larger prey to satisfy their metabolic needs. Larger seals also dived frequently to the deep OMZ, possibly because of a greater diving ability than smaller seals, suggesting their dependency on food in the deeper depth zones. Video observations showed that seals encountered the rarely reported ragfish (Icosteus aenigmaticus) in the depths of the OMZ, which failed to show an escape response from the seals, suggesting that low oxygen concentrations might reduce prey mobility. Less mobile prey in OMZ would enhance the efficiency of foraging in this zone, especially for large seals that can dive deeper and longer. We suggest that the OMZ plays an important role in structuring the mesopelagic ecosystem and for the survival and evolution of elephant seals.     

Water-soluble vitamin homeostasis in fasting northern elephant seals (Mirounga angustirostris) measured by metabolomics analysis and standard methods

Despite the importance of water-soluble vitamins to metabolism, there is limited knowledge of their serum availability in fasting wildlife. We evaluated changes in water-soluble vitamins in northern elephant seals, a species with an exceptional ability to withstand nutrient deprivation. We used a metabolomics approach to measure vitamins and associated metabolites under extended natural fasts for up to 7 weeks in free-ranging lactating or developing seals. Water-soluble vitamins were not detected with this metabolomics platform, but could be measured with standard assays. Concentrations of measured vitamins varied independently, but all were maintained at detectable levels over extended fasts, suggesting that defense of vitamin levels is a component of fasting adaptation in the seals. Metabolomics was not ideal for generating complete vitamin profiles in this species, but gave novel insights into vitamin metabolism by detecting key related metabolites. For example, niacin level reductions in lactating females were associated with significant reductions in precursors suggesting downregulation of the niacin synthetic pathway. The ability to detect individual vitamins using metabolomics may be impacted by the large number of novel compounds detected. Modifications to the analysis platforms and compound detection algorithms used in this study may be required for improving water-soluble vitamin detection in this and other novel wildlife systems.     

Hormone and metabolite changes associated with extended breeding fasts in male northern elephant seals (Mirounga angustirostris)

We measured metabolic hormones and several key metabolites in breeding adult male northern elephant seals to examine the regulation of fuel metabolism during extended natural fasts of over 3 months associated with high levels of energy expenditure. Males were sampled twice, early and late in the fast, losing an average of 23% of body mass and 47% of adipose stores between measurements. Males exhibited metabolic homeostasis over the breeding fast with no changes in glucose, non-esterified fatty acids, or blood urea nitrogen. Ketoacids increased over the fast but were very low when compared to other fasting species. Changes within individuals in total triiodothyronine (tT₃) were positively related to daily energy expenditure (DEE) and protein catabolism. Differences in levels of thyroid hormones relative to that observed in weaned pups and females suggest a greater deiodination of T₄ to support the high DEE of breeding males. Relative levels of leptin and ghrelin were consistent with the suppression of appetite but a significant reduction in growth hormone across the fast was contrary to expectation in fasting mammals. The lack of the increase in cortisol during fasting found in conspecific weaned pups and lactating females may contribute to the ability of breeding males to spare protein despite high levels of energy expenditure. Together these findings reveal significant differences with conspecifics under varying nutrient demands, suggesting metabolic adaptation to extended high energy fasts.     

Angiotensin II and aldosterone increase with fasting in breeding adult male northern elephant seals (Mirounga angustirostris)

The renin-angiotensin-aldosterone system (RAAS) appears to contribute significantly to osmoregulation of fasting northern elephant seal (Mirounga angustirostris) pups; however, RAAS has not been characterized in fasting adult seals. Therefore, this study examined the contribution of RAAS to water turnover rates in fasting adult male northern elephant seals. Blood samples were obtained twice during their breeding fast at an interval of 6.5 wk, and water efflux rate was estimated by isotopic dilution during the same period. Serum electrolytes (Na+, K+, Cl-) and osmolality were unaltered between the two sampling periods, indicating ionic and osmotic homeostasis during the fast. Despite the lack of an increase in vasopressin, serum angiotensin II and aldosterone were increased and were significantly and positively correlated. Changes in aldosterone concentration and water efflux rate were significantly and negatively correlated, suggesting that the greater the increase in aldosterone, the smaller the loss of water. Adult male seals maintain ionic and osmotic homeostasis similar to that of fasting weaned pups, and this homeostasis appears to be mediated, at least in part, by RAAS, which probably contributes to increased water retention as well. The hormonal mechanisms by which northern elephant seals maintain water and electrolyte balance during fasting conditions appear to be similar regardless of age.     

Immobilization of adult male southern elephant seals (<Emphasis Type="Italic">Mirounga leonina</Emphasis>) during the breeding and molting periods using a tiletamine/zolazepam mixture and ketamine

Seventy-seven immobilizations were carried out on adult male southern elephant seals at Stranger Point, Isla 25 de Mayo (King George Island) using a combination of Zoletil^® (tiletamine and zolazepam) and ketamine in order to obtain biological samples. During 2006/2007, 22 males were immobilized at the beginning of their breeding period (EB), 19 of which were recaptured at the end of breeding (LB). Four were given only once at an unknown stage of breeding (USB) and 18 males were immobilized at the beginning of molting (BM). During 2007/2008, 14 adult males were immobilized at an USB. Zoletil^® was administered using an automatic discharge device, whereas ketamine was injected directly with a syringe, and was used only when the initial sedation was not enough to carry out the programmed sampling. The initial mean dose of Zoletil^® was 1,387 ± 304 mg, which represented 0.60 ± 0.14 mg/kg, range 0.36–1.05, n = 77. In 47 procedures, an average dose of 1.04 ± 0.66 mg/kg of ketamine was added. Mean immobilization time was 34 ± 14 min. In 25 out of the 77 procedures, males showed apnea, which lasted 8 ± 4 min (range 2–15 min). The necessary doses of Zoletil^® and ketamine to attain immobilization differed between stages. For animals taken twice, doses (mg/kg) of Zoletil^® and ketamine were significantly higher at the beginning than at the end of breeding. During molting, the doses of Zoletil^® given were significantly lower than those used during breeding, although the proportion of animals that required ketamine during molting was significantly higher than during breeding. Zoletil^® proved to be a safe immobilizing agent for field work on adult males of this species, given the wide range of doses used without any serious consequences. Furthermore, the addition of ketamine was useful when the initial sedation was not satisfactory or for prolonging the immobilization period in a practical and reliable way.     

Characterization of postdive recovery using sound recordings and its relationship to dive duration,exertion, and foraging effort of southern elephant seals (Mirounga leonina)

It is notoriously difficult to measure physiological parameters in cryptic free‐ranging marine mammals. However, it is critical to understand how marine mammals manage their energy expenditure and their diving behavior in environments where the predation risks are low and where survival is mainly linked to capacities to maintain physiological homeostasis and energy budget balance. Elephant seals are top marine predators that dive deeply and continuously when at sea. Using acoustic recorders deployed on two postbreeding southern elephant seals (SES) females, we developed methods to automatically estimate breathing frequency at the surface. Using this method, we found that seals took successive identical breaths at high frequency (0.29 Hz) when recovering at the surface and that breath count was strongly related to postdive surfacing time. In addition, dive depth was the main factor explaining surfacing time through the effects of dive duration and total underwater swimming effort exerted. Finally, we found that recovery does not only occur over one dive timescale, but over a multidive time scale for one individual. The way these predators manage their recovery will determine how they respond to the change in oceanic water column structure in the future.     

Marking and monitoring studies of the Kerguelen stock of southern elephant seals Mirounga leonina and their bearing on biological research in the Vestfold Hills

Southern elephant seals Mirounga leonina breed and moult on many subantarctic islands during the austral spring and summer. In the Kerguelen Province the subpopulations of M. leonina at Kerguelen (49°21S, 70°12E), Marion (46°54S, 37°45E) and Possession (46°25S, 51°45E) Islands have declined since 1970 and their present status at Heard Island (53°05S, 73°30E) is unknown. Population studies during their terrestrial phase have failed to explain the declines. Long distance movements of individuals between the subpopulations in question and also the Vestfold Hills, Antarctica (68°35S, 77°58E) have been recorded. The availability of food resources, competition with rapidly increasing fur seal populations and competition with fishing fleets have all been implicated in their decline. These explanations assume that communal feeding grounds are utilized. As they are predators entirely dependent on marine feeding, a study of their spatial and temporal distribution during their pelagic existence is of the utmost importance. Parameters describing growth, reproduction rates, population dynamics, and feeding ecology of the subpopulations in the Kerguelen Province may furthermore serve as indices of change within the marine ecosystem. The presence of a relatively large and predominantly male nonbreeding population of M. leonina at the Vestfold Hills in Antarctica which originates from the Kerguelen/Heard Island group, and which shows annual return, should be included in the marking and monitoring studies of the Kerguelen stock of southern elephant seals. Studies here, including an update of the size and social structure of the Heard island subpopulation, may elucidate the observed decline of, in particular, the adult bull component of the breeding stock.     

Development of individual recognition of female southern elephant seals, Mirounga leonina, from Punta Norte Península Valdés, applying principal components analysis

Aim The development of software able to provide individual recognition of southern elephant seals, as a tool to study colonies. This analysis was performed within a framework of studies concerning environmental dispersion produced by the El Niño Southern Oscillation effect in the Southern Ocean Ecosystem. Location Digital photographs of reproductive female elephant seals were taken at Punta Norte (Península Valdés, Patagonia; 42°05′ S, 63°45′ W) during the 2002 breeding season (August to November). The data set under analysis is composed of 96 elephant seal images for a population of 56 individuals. Method Identification of specimens was carried out using digital pictures taken with a digital video camera, and processed through the ‘Eigenfaces’ method, which is based on principal components analysis. Special care was taken to control possible variations among images of the same individual, like distance, angle, light intensity, etc. To deal with these variations, an initial alignment procedure is proposed to have all images framed; in addition an initial histogram equalization was used which attenuates any potential variation in light intensity. The software was developed in IDL5.5 language. Results A complete set of empirical results is displayed showing the potential effectiveness of this technique. Individual recognition and pertinence to different population subsets (harems) tests have been carried out. A principal result of this work is that all 96 elephant seal images (representing 56 individuals) were correctly identified. Conclusion The Eigenfaces method can be used successfully for identification of elephant seals. With the appropriate preparatory treatment of images, high performance results can be expected.     

Prey selection of subadult male northern fur seals (Callorhinus ursinus) and evidence of dietary niche overlap with adult females during the breeding season

During the breeding season northern fur seals (Callorhinus ursinus) congregate on the Pribilof Islands in large numbers creating the potential for intraspecific competition. Due to the declining trend in the Pribilof Islands population of fur seals, it is important to understand how prey resources are partitioned among the population. Fur seals exhibit a high degree of sexual dimorphism resulting in energetic differences among age and sex classes. Therefore, we hypothesized that subadult male and adult female fur seals would differ in the type and size of prey consumed. We examined the diets of subadult male (age 2–8; mean mass 28–176 kg) and adult female (age ≥ 3 yr; mean mass 13–50 kg) seals on St. Paul Island from 1992 to 2000. Prey remains found in fecal samples were compared using niche overlap indices. There was nearly complete dietary niche overlap between subadult male and adult female fur seals. Walleye pollock (Theragra chalcogramma), Pacific salmon (Oncorhynchus spp.), Pacific herring (Clupeia pallasi), and cephalopods were common prey items found in the diets of both groups. We found differences in the size of pollock consumed and that geographic location of sample collection may be important in determining diet differences. Our results indicate high levels of dietary overlap among subadult male and adult female fur seals.     

Impact of body reserves on energy expenditure, water flux, and mating success in breeding male northern elephant seals

In capital breeders, individual differences in body size and condition can impact mating effort and success. In addition to the collateral advantages of large body size in competition, large nutrient reserves may offer advantages in endurance rivalry and enable the high rates of energy expenditure associated with mating success. We examined the impacts of body reserves and dominance rank on energy expenditure, water flux, mating success, and breeding tenure in the adult male northern elephant seal, a polygynous, capital breeder. Adult males expended energy at a rate of 159 ± 49 MJ d (-1), which is equivalent to 3.1 times the standard metabolic rate predicted by Kleiber's equation. Despite high rates of energy expenditure and a long fasting duration, males spared lean tissue effectively, deriving a mean of 7% of their metabolism from protein catabolism. Body composition had a strong impact on the ability to spare lean tissue during breeding. When controlling for body size, energy expenditure, depletion of blubber reserves, and water efflux were significantly greater in alpha males than in subordinate males. Large body size was associated with increased reproductive effort, tenure on shore, dominance rank, and reproductive success. Terrestrial locomotion and topography appeared to strongly influence energy expenditure. Comparisons with conspecific females suggest greater total seasonal reproductive effort in male northern elephant seals when controlling for the effects of body mass. In polygynous capital breeding systems, male effort may be strongly influenced by physiological state and exceed that of females.     

Local weather and body condition influence habitat use and movements on land of molting female southern elephant seals (Mirounga leonina)

Southern elephant seals (Mirounga leonina) are known to move and aggregate while molting, but little is known about their behavior on land during this time. In this study, 60 adult females were monitored (23 with GPS tags) during four molting seasons, between 2012 and 2016 at Kerguelen Archipelago, Indian Ocean. Population surveys were recorded each year (N = 230 daily counts), and habitat use was analyzed in relation to the stage of the molt and local weather. Based on stage of molt, habitat use, and movements on land, we classified the molt of elephant seals into three phases: (1) a “search phase” at the initial stage of molt when grass and wallow habitats were used and characterized by greater mean distances travelled on land per day compared with the two other phases; (2) a “resident phase”: during initial and mid‐stage of molt when animals were found in grass and wallow habitats but with less distance moved on land; and (3) a “termination phase” at the final stage of molt where grass and beach habitats were occupied with no change in distances. Windchill and solar radiation influenced individual distances moved per day (mean 590 ± 237.0 m) at the mid‐ and final stage of molt such that animals travelled greater distances on days of low windchill or high solar radiation. Individual variation in distance moved and relative habitat use were also linked to body mass index (BMI) at arrival on the colony, as females with higher BMI moved less and preferred beach habitat. Moreover, the individual rate of molt increased with the use of wallows. Aggregation rate tended to be negatively correlated with distances moved. We therefore suggest that individuals face an energetic trade‐off while molting, balancing energy expenditure between movement and thermoregulation.     

Surface temperature patterns in seals and sea lions: A validation of temporal and spatial consistency

We assessed infrared thermography (IRT) as a tool for evaluating spatial and temporal surface temperature patterns in juvenile female harbor seals (Phoca vitulina, n=6) and adult female Steller sea lions (Eumetopias jubatus, n=2). Following a technical assessment of the influence of environmental parameters on the specific camera to be used, we identified regional and seasonal variability of surface temperatures. Variation was observed in several seasonal transitions (winter, reproductive, molt) in ten monitored body regions. Spatially and temporally consistent thermal patterns in the shoulder, axillae, foreflipper and hindflipper suggest thermal windows in both species.     

Foraging habitats based on the diet of female northern fur seals (Callorhinus ursinus) on the Pribilof Islands, Alaska

Scats (fecal samples) collected between 1987 and 2000 on northern fur seal Callorhinus ursinus rookeries of St Paul ( n =2968) and St George Islands ( n =1203), Alaska, were used to examine the relationship between breeding sites and food habits of adult female seals. On the basis of the frequency of occurrence (FO) and per cent minimum number of individual prey (%MNI) in scats, juvenile walleye pollock Theragra chalcogramma and gonatid squid Gonatopsis borealis/Berryteuthis magister and Gonatus madokai/Gonatus middendorffi were the dominant prey species consumed overall. Other primary prey (FO>5%) included Pacific sand lance Ammodytes hexapteus , Pacific herring Clupea pallasi , northern smoothtongue Leuroglossus schmidti , Atka mackerel Pleurogrammus monopterygius , Pacific salmon ( Oncorhynchus spp.) and other squid of the Gonatus genus. We identified five rookery complexes from a cluster analysis of the FO of primary prey in scats. Rookery complexes were separated geographically and each was further defined by characteristic patterns in the representation of prey types typically associated with specific hydrographic domains. Diet differences were observed among rookeries on the north and south side of St George Island and on the east, south and south-west side of St Paul Island. The rookery clusters observed in this study provide evidence of resource partitioning among adult female northern fur seals and have important implications for fur seal conservation and management.