Adult Seals Research Articles

Movement, diving, and haul-out behaviors of juvenile bearded seals in the Bering, Chukchi and Beaufort seas, 2014–2018

Bearded seals (Erignathus barbatus) are abundant in the Pacific Arctic and are an important subsistence resource for many Alaska Native communities. The Pacific Arctic is warming rapidly with substantial consequences predicted for ice-associated marine mammals, such as the bearded seal, which led to its 2012 listing as Threatened under the U.S. Endangered Species Act. We provide the most comprehensive description of juvenile bearded seal movement, diving, and haul-out behaviors for the Pacific Arctic, obtained from 24 seals tagged with satellite-linked data recorders along Alaska’s coast from 2014 to 2018. Most seals (19 of 24) made north–south movements with the seasonal extent of sea ice, however, all three seals tagged north of Bering Strait made minimal north–south movements and two seals tagged in the Bering Sea moved north as sea ice advanced south. All seals primarily occupied shallow coastal waters and areas with intermediate-concentration pack ice or that were near the ice edge. Seals spent half their time near the sea floor. Hauling out occurred less in the winter and increased during spring and summer, coinciding with the annual molting period. When ice was at its minimum extent, seven seals frequently hauled out on land. Juvenile bearded seals made use of much of the continental shelf in the Bering, Chukchi and Beaufort Seas, and their use of a broad range of ice concentrations and willingness to haul out on land suggests some resilience to changing sea ice conditions. However, whether the behaviors we documented in juveniles are similar for adult bearded seals remains unclear.

Variation in habitat use of Beaufort Sea polar bears

Habitat loss and climate change are major processes affecting biodiversity, especially in the Arctic which is experiencing rapid sea ice decline. Loss of sea ice habitat for ice-dependent species such as polar bears (Ursus maritimus) has been associated with declines in body condition, reproductive output, survival, and abundance. Monitoring habitat use can therefore provide insights into population responses to sea ice loss, especially for vulnerable demographic groups such as subadults. Here, we used resource selection functions to examine habitat selection patterns of subadult male and female (n = 21) and adult female (n = 37) polar bears in the Southern Beaufort Sea population from 2007 to 2011. We found that polar bears displayed broad similarities in seasonal habitat selection by using nearshore areas in winter/spring and ranging farther offshore into the multiyear ice in summer/autumn. However, there were differences in habitat use among age, sex, and reproductive classes. Adult females with cubs-of-the-year differed the most among classes and selected landfast ice in spring, allowing them to hunt for seal birth lairs while reducing risk of intra-specific predation. Adult females with older cubs and solitary adult females used active sea ice, which allowed them to hunt adult seals, while subadult females used a mix of active and landfast ice. Subadult males had similar selection for landfast ice as females with cubs-of-the-year, potentially as a mechanism to reduce intra-specific competition and/or kleptoparasitism. The Arctic faces continued warming and understanding variation in habitat use patterns can assist in identifying which bears are most vulnerable to loss of different sea ice habitats.

Leopard seal diets in a rapidly warming polar region vary by year, season, sex, and body size

BackgroundResolving the preferred prey items and dietary proportions of leopard seals is central to understanding food-web dynamics in the rapidly-warming Antarctic Peninsula region. Previous studies have identified a wide range of prey items; however, due to anecdotal or otherwise limited information, leopard seal diets remain unresolved by seal sex, individual, body size, region, and season. Over the 2013, 2014, and 2017 field seasons we collected scat, tissue samples (red blood cells and plasma; n = 23) for stable isotope analyses, and previously-reported animal-borne video from 19 adult leopard seals foraging near mesopredator breeding colonies at Cape Shirreff, Livingston Island. We summarized a priori diet information from scat and video analysis and applied a three-isotope (δ13C, δ15N, δ34S), four-source (fish, fur seal, krill, penguin) Bayesian mixing model to examine temporal variability in both prey sources and leopard seal tissues.ResultsThe austral spring diets of males and females focused on Antarctic krill (31.7–38.0%), notothen fish (31.6–36.5%), and penguin (24.4–26.9%) and were consistent across all 3 years. Several lines of evidence suggest the transition to summer foraging was distinct for males and females. Female diets transitioned rapidly to higher δ15N values (+2.1‰), indicating increased consumption of penguin (29.5–46.2%) and energy-dense Antarctic fur seal pup (21.3–37.6%).ConclusionsThe seasonal increase in leopard seal δ15N values, and thus fur seal in their diet, was predictably related to larger body size; it may also be forcing reductions to the largest Antarctic fur seal colony in the Antarctic Peninsula. Our ensemble sampling approach reduces historical biases in monitoring marine apex predator diets. Further, our results are necessary to best inform regional fisheries management planning.

Site use and connectivity of female grey seals (Halichoerus grypus) around Wales

Grey seals (Halichoerus grypus) are a qualifying feature of three special areas of conservation (SACs) in Wales, yet relatively little is known of their site use along this coastline. Since 1992, many individuals and organisations have contributed to a grey seal photographic identification database held by Natural Resources Wales, which is one of the largest and oldest of its kind, providing key information from grey seal haul-out sites around the Celtic and Irish Seas. Here, we investigated spatial connectivity of haul-out sites and fidelity of adult females to breeding sites. The minimum number of adult female grey seals using the area between 1992 and 2016 was 2688. Individual capture histories and relative spatial transition probabilities (Pij) between pairs of location groups were calculated. Adjacent locations were highly connected (e.g. Lleyn Peninsula and Bardsey, Pij = 0.7) but connections spanned the entire region, up to 230 km apart (e.g. Skomer and Dee Estuary, Pij = 0.004). Resights were recorded within SACs (e.g. Lleyn Peninsula and Bardsey [Lleyn Peninsula and the Sarnau SAC], Pij = 0.7), between SACs (e.g. Bardsey and Skomer [Pembrokeshire Marine], Pij = 0.03), between SACs and non-designated areas (e.g. Skerries and Bardsey, Pij = 0.09) and between sites outside any protected area (e.g. Dee Estuary and Anglesey, Pij = 0.5). While inter-annual fidelity to breeding sites was high (Pij = 0.82–1), individual female grey seals moved throughout the region. This evidence of extensive site use beyond protected areas is important for the management and conservation of grey seals around Wales.

Deep diving harbor seals (Phoca vitulina) in South Greenland: movements, diving, haul-out and breeding activities described by telemetry

Harbor seals (Phoca vitulina) were formerly widely distributed in Greenland, but in most areas, they have now become rare or extinct. In this study, we deployed 15 satellite-linked data-recorders on 12 individual harbor seals captured near the southern tip of Greenland. The tagging site, a small archipelago, turned out to be their main haul-out and molting location. The seals were tagged around the first week of September across 2 years. Six adult seals transmitted during the breeding season (June–July), during which two males and a female stayed near the tagging site, whereas two females and a male made a targeted swim about 250 km northward along the east coast, just prior to parturition and they returned right after the breeding period. Based on behavior (strong site fidelity and abrupt changes in haul-out and diving activities), we determined that all three females gave birth and that parturition happened during 14–21 June. Prolonged haul-out, relating to the molt, started in early August and peaked during 15 August–8 September with an average of 10–11 h haul-out per day. The seals thereafter gradually transitioned toward a winter mode with more deep dives and on average hauling out 4 h every other day. Dives deeper than 400 m made up less than 1% of their dives, but four seals dove to depths in excess of 575 m, with a record depth of 631 m and the longest dives lasting between 20 and 25 min. To our knowledge, these dives are the deepest recorded for harbor seals.

The ecological and behavioral significance of short-term food caching in polar bears (Ursus maritimus)

The paucity of observations of wild polar bears (Ursus maritimus) caching of food (including hoarding, i.e., burying and remaining with a kill for up to a few days) has led to the conclusion that such behavior does not occur or is negligible in this species. We document 19 observations of short-term hoarding by polar bears between 1973 and 2018 in Svalbard, Greenland, and Canada. Short-term hoarding appears to be influenced by size of the kill and its remaining energetic value after the first meal has been consumed. Fat and meat from smaller seals, such as pup or yearling ringed seals (Pusa hispida), are largely devoured immediately, leaving little to hoard. Carcasses of adult ringed seals, harp seals (Pagophilus groenlandicus), and bearded seals (Erignathus barbatus) may be covered with snow to reduce the chance of kleptoparasitism by another bear or other scavengers visually detecting a dark spot on the ice, while the hoarding bear lies nearby. Hoarding of other species, such as beluga (Delphinapterus leucas) (calves or parts) or other polar bears, appears opportunistic. We review differences in caching, including short-term hoarding behavior between polar bears and brown bears (U. arctos), and hypothesize about factors that may have influenced their evolution.

Long-Term Stability in the Trophic Ecology of a Pelagic Forager Living in a Changing Marine Ecosystem

Natural or human-induced environmental changes can modify the structure of ecological communities and thus alter food web interactions. After the collapse of hake stocks (Merluccius hubbsi) provoked by fisheries over the Patagonian shelf in 1997 profound changes have taken place in the community, including long-term dietary shifts in some marine vertebrate predators. Stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in bone collagen of subadult and adult male South American fur seals (Arctocephalus australis) were measured for the period 1976-2017 to investigate if the changes occurred in the marine community from northern and central Patagonia affected the diet of this predator. Suess corrected δ13C values and δ15N values in bone collagen of fur seals did not change significantly over the study period. According to this, male fur seals have remained as pelagic foragers without changing their trophic position nor switching their main preys in the Patagonian food web over the last four decades. This long-term stability in the diet of fur seals contrasts with dietary changes reported for benthic foragers in the region. Although long-term diet studies are restricted to a few marine predators in the region, current evidence suggests that benthic-demersal foragers were more prone to dietary shifts than pelagic ones after perturbations that occurred in the marine community of northern and central Patagonia.

Fur and faeces – Routes of mercury elimination in the Baltic grey seal (Halichoerus grypus grypus)

This study focused on evaluating the elimination of Hg by Baltic grey seals (Halichoerus grypus grypus) via faeces and pelage. In addition, we investigated the potential for ecosystem contamination via these routes. Faeces and fur were collected in 2014–2017 from captive adult grey seals and their pups. The concentrations of total mercury (THg) and methylmercury (MeHg) were measured in the samples. The amount of mercury eliminated in a labile form (the sum of the bioavailable Hg(II) and methylmercury) was also determined. An adult seal removed about 46% of mercury supplied with food via the faeces, of which only 17% was MeHg. Considering that mercury is mainly supplied to the body as MeHg, it can be assumed that mercury excreted along with faeces has undergone transformation inside the animal body. Despite the much higher THg and MeHg concentrations measured in fur, the incorporation of mercury into newly formed fur is a less effective method of Hg elimination removing just 4% of mercury entering the body via the alimentary route. The presence of mercury in lanugo is evidence of maternal transfer. First droppings of the pups were characterised by the highest content of MeHg and a low THg concentration. Then, despite the limited supply of mercury with food, and the rapid growth of the pup, the concentration of THg increased, suggesting that mercury started to be transformed into less toxic forms.It was estimated that faeces and fur expelled by seals could deliver about 800 g of mercury to the Baltic Sea. For both faeces and fur, most of the mercury (>95% for excrements and >85% for fur) was expelled in a labile form that can be quickly recycled.

The diet of Weddell seals (Leptonychotes weddellii) in Terra Nova Bay using stable isotope analysis

Stable isotope analyses were used to investigate the diet of Weddell seals in Terra Nova Bay (Ross Sea) and the potential variation of their foraging behaviour with age, sex and body mass. For this purpose, skin samples were collected from adult breeding seals and pups, together with muscle samples of their potential prey. Our results showed variation in foraging behavior between age classes, with pups reporting lower δ13C values than adults, while no significant differences in δ15N were recorded. In addition, contrary to expectations, a mixing model analysis showed that adult seals foraged mainly on shallow benthic prey, such as Trematomus spp. (34.1%) and Dissostichus mawsoni (21.1%), rather than on pelagic fish, such as Pleuragramma antarcticum (9.8%). Overall, with this paper we provide novel diet information on a seal colony not previously sampled, adding new insight into the feeding ecology of a top Antarctic predator.

Thermoregulatory costs in molting Antarctic Weddell seals: impacts of physiological and environmental conditions: Themed Issue Article: Conservation of Southern Hemisphere Mammals in a Changing World.

For polar marine mammals, the energetic cost of thermoregulation depends on ambient conditions in the highly variable surrounding environment. Heat conservation strategies used by pinnipeds to reduce total heat loss include small surface area to volume ratios, the ability to limit perfusion and thick subcutaneous blubber layers. There are limits to how cool the skin surface may remain without compromising function, especially during the annual pelage molt, when hair and skin are replaced. To determine if actively molting seals incur higher thermoregulatory costs, surface temperature (ST) and heat flux (HF) were measured in 93 adult female Weddell seals (Leptonychotes weddellii) both prior to and during the active molting period using direct sensors and infrared imaging. Linear mixed-effect models revealed that ST increased significantly with increased ambient temperature and decreased wind speed (contributing 44.6 and 41.7% of the attributed variance, respectively). Seal STs were not impacted by molt status, but were maintained at 11.2 ± 0.3°C warmer than the ambient temperature. Infrared imaging results averaged 15.1 ± 1.4°C warmer than direct ST measurements. In contrast, HF was significantly higher in seals in early molting stages compared to the pre-molt season ( P < 0.001) and molt status accounted for 66.5% of the variance in HF. Thermoregulatory costs calculated from estimated basal metabolic rate and measured HF were more than double for molting seals as compared to those in pre-molt. This suggests that perfusion is increased during molt to support follicle development, despite the increased energetic costs associated with higher HF rates. Because ST, HF and thermoregulatory costs are strongly influenced by ambient conditions, molt timing is likely under selective pressure to occur during the warmest period of the year. Shifts in environmental conditions that delay molt phenology or increase HF rates could negatively impact seal populations by further increasing thermoregulatory costs.

Blood plasma chemistry in White Sea bearded seals across different age groups

Blood chemistry values are reported for the bearded seal species (Erignathus barbatus barbatus Erxleben, 1777) from the White Sea. 27 blood plasma indices are used to describe the state of the metabolism of proteins, carbohydrates, lipids, minerals (total protein, albumin, α-, β-, γ-globulins, urea, creatinine, uric acid, glucose, lactic acid, total lipids, triglycerides, cholesterol, calcium, phosphorus, sodium, potassium, magnesium, iron, copper, chlorides, aspartate aminotransferase, alanine aminotransferase, γ-glutamyl transferase, creatine kinase, alkaline phosphatase, lactate dehydrogenase) in 3-, 5- and 10-year-old seals. The values of the studied parameters are similar to published data for bearded seal populations in other Arctic regions, as well as being in close agreement with indicators of other pinniped species of the same age. The plasma content of total protein, albumin, α-, β-, γ-globulins, urea, uric acid, total lipids, calcium, magnesium, sodium, and chlorides is invariable in animals of the studied ages. In common with other pinnipeds and land-based mammals, age-related changes in metabolic rates in the studied animal groups are most pronounced in the activity level of key metabolism enzymes. While aspartate aminotransferase, alanine aminotransferase and γ-glutamyl transferase activity is higher in adult seals than in immature animals, alkaline phosphatase, creatine kinase and lactate dehydrogenase activity is lower. Changes in biochemical parameters of bearded seal blood at the ages of 3, 5 and 10 years indicate a catabolic orientation in metabolism at all studied development stages. Although more research is needed to investigate the biological significance of a number of blood indices, the data presented in this study provide initial baseline blood chemistry parameters for use in assessing the condition of individual seals, as well as informing monitoring and management efforts for wild seal populations.

Lifetime coastal and oceanic foraging patterns of male Guadalupe fur seals and California sea lions

AbstractCarcasses of adult and subadult male Guadalupe fur seals (GFSs) are beached on Isla Magdalena, representing about 73% of all GFSs beachings since 2003. Analysis of carbon and nitrogen stable isotopes in dentin collagen from male GFSs was used in an attempt to distinguish animals from two possible locations of origin: the oceanic Guadalupe Island (GI) and the coastal San Benito Islands (SBI). Samples of conterminous and contemporary California sea lions (CSLs) were included as representative of coastal predators. Two distinct groups of GFSs were evident based on δ13C values: coastal GFSs with higher δ13C values than CSLs, and oceanic GFSs with lower δ13C values than CSLs. Significant temporal trends were observed in the δ15N values; values for oceanic GFSs and CSLs increased annually (0.082‰ and 0.089‰, respectively), while those for coastal GFS decreased annually by 0.183‰. The isotopic segregation of oceanic and coastal GFS males, presumably from GI and SBI respectively, has been present at least since the mid‐1990s. This segregation may be due to dissimilar ingestion of prey from oceanic vs. coastal origin prior to their seasonal co‐occurrence in the Gulf of Ulloa.

Seasonal variability and individual consistency in gray seal (Halichoerus grypus) isotopic niches

Although it is often assumed that individuals in generalist populations are equivalent, recent research indicates that individual dietary specialization can be common in marine predators. Gray seals (Halichoerus grypus (Fabricius, 1791)) were considered locally extinct in United States waters by 1958 but have since recolonized the region. Although considered generalists, less is known about gray seal foraging ecology in the United States. To address this, we used carbon and nitrogen stable isotope analyses to investigate the foraging niches of adult gray seals in Massachusetts, USA. We examined skin, fur, and blood components to investigate seasonal variability and individual consistency in foraging niches, and serially sampled vibrissae to quantify the degree of individual foraging specialization in this population. Our results suggest that seals shift from coastal foraging habitats before molt to offshore habitats after molt, with a coincident shift from higher to lower trophic-level prey. Adult gray seals also exhibited individual consistency in foraging niches independent of population-level shifts and reflect a generalist population composed of individual foraging specialists. These findings serve as a baseline for subsequent research on gray seals in United States waters that could help to determine the mechanisms which promote individual specialization in this population.

Trace Element Concentrations in Livers of Pacific Harbor Seals (Phoca vitulina richardii) from San Juan County, Washington, USA

Approximately 5,000 Pacific harbor seals (Phoca vitulina richardii) reside year-round in San Juan County (SJC), Washington (US) in the center of the binational Salish Sea. We retrospectively analyzed total cadmium (Cd), copper (Cu), iron (Fe), mercury (Hg), magnesium (Mg), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in livers of dead stranded harbor seals (n=57) collected in SJC between 2009 and 2012 to identify age-related and regional patterns of trace element exposure. Consistent with prior studies of contaminants in pinnipeds, Hg, Cd, and Se concentrations increased with age, and Se:Hg molar ratios approached 1:1 in adult seals. Concentrations of Cd and Hg were below putative marine mammal toxicity thresholds. Mercury concentrations were comparable among Salish Sea populations. Although SJC is less urbanized with fewer industrial inputs than South Puget Sound (SPS), SJC nonpups had greater concentrations of Cd, Cu, and Zn, and pups had greater concentrations of Zn compared to SPS seals. We hypothesize these regional differences could be due to prey preference and availability or to natural geochemical processes. Reported concentrations inform future sampling protocols and can assist in tracking long-term temporal and spatial trends of trace elements in marine organisms.

Identifying foraging habitats of adult female long-nosed fur seal Arctocephalus forsteri based on vibrissa stable isotopes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 628:223-234 (2019) - DOI: https://doi.org/10.3354/meps13113 Identifying foraging habitats of adult female long-nosed fur seal Arctocephalus forsteri based on vibrissa stable isotopes Dahlia Foo1,*, Mark Hindell1, Clive McMahon2, Simon Goldsworthy3 1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania 7004, Australia 2Sydney Institute of Marine Science, Mosman, New South Wales 2088, Australia 3Aquatic Sciences Centre, South Australian Research and Development Institute, West Beach, South Australia 5024, Australia *Corresponding author: dahlia.foo@utas.edu.au ABSTRACT: We investigated how foraging ecotypes of female long-nosed fur seals Arctocephalus forsteri could be identified from vibrissa stable isotopes. We collected regrowths of vibrissae from adult females (n = 18) from Cape Gantheaume, Kangaroo Island, South Australia, from 2 breeding seasons (2016, 2017). The period represented by the regrowth was known, and 8 individuals were administered with 15N-enriched glycine as a biomarker to mark the start date of the regrowth. Non-glycine-marked and glycine-marked vibrissae were used to estimate the rate of the individual vibrissa regrowth. Using individual growth rates (0.18 ± 0.04 mm d-1), we reconstructed a stable isotope (δ13C and δ15N) time series for each regrowth and allocated them to corresponding at-sea locations either based on geolocation tracks (n = 14) or foraging habitat type (shelf or oceanic) based on diving data (n = 2) of the sampled seals. Mean (±SD) δ15N from vibrissa segments was higher when females foraged on the continental shelf region (16.1 ± 0.7‰, n = 29) compared to oceanic waters (15.1 ± 0.7‰, n = 106) in 2017, whereas it was similar in both regions in 2016 (shelf: 15.3 ± 0.4‰, n = 13; oceanic: 15.4 ± 0.4‰, n = 15). Based on the stable isotope signatures of vibrissa segments, model-based clustering analysis correctly classified 79.8% as originating from shelf or oceanic foraging habitats. This demonstrates the potential of using vibrissa stable isotopes for studying the foraging ecology of an important top marine predator. KEY WORDS: Isoscape · Foraging strategies · Trophic dynamics · Continental shelf · Oceanic · Marine top predators Full text in pdf format Supplementary material PreviousCite this article as: Foo D, Hindell M, McMahon C, Goldsworthy S (2019) Identifying foraging habitats of adult female long-nosed fur seal Arctocephalus forsteri based on vibrissa stable isotopes. Mar Ecol Prog Ser 628:223-234. https://doi.org/10.3354/meps13113 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 628. Online publication date: October 10, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Vocal behavior in spotted seals (Phoca largha)

Captive studies can inform passive acoustic monitoring efforts by describing fundamental features of species-typical vocalizations emitted by known individuals. These include acoustic parameters as well as developmental, seasonal, and sex-based patterns in vocal behavior. Here, two male spotted seals were studied in captivity from age 3 months through 8 years. Vocal behavior was scored daily and opportunistically recorded. The production of underwater calls emerged with presumed sexual maturity (age 4). To evaluate vocal repertoire and fine-scale temporal patterns of sound production in adult seals, an underwater acoustic recorder was continuously deployed with these seals at age 7–8 years. The spotted seals produced a variety of underwater calls—including roars, knocks, and moans—with dominant energy below 1 kHz. There was a marked annual peak in vocal activity in spring, prior to the yearly molt. This period coincided with increased aggressive behavior and musky odor indicative of heightened reproductive activity. These results from developing male spotted seals, obtained in the absence of conspecific females, confirm the production of recognizable, stereotypic underwater calls associated with the breeding season. These findings can be used to inform the use of autonomous acoustic recorders to track the presence and movements of free-ranging seals in remote habitats.

Behavioural ontogeny of bearded seals Erignathus barbatus through the first year of life

Pinniped pups face special ontogenetic challenges as they are born and receive maternal care on solid substrates (land or ice) but must transition to feeding aquatically following weaning. In this study, satellite relay data loggers were used to study behavioural ontogeny of bearded seal Erignathus barbatus pups (n = 13) through their first year in Svalbard, Norway. Pups occupied shallow, coastal habitats and were found in areas with intermediate ice concentrations (in seasons with sea ice: late-autumn/winter). Most pups showed exploratory movement patterns that peaked in the weeks following weaning; maximum home range size occurred at 31 to 60 d of age. Thereafter, home range size decreased with pups settling into areas along the coast. Time spent diving, dive duration, dive depth and time at the bottom of dives increased during the first weeks of independence, stabilizing when pups were ~50 d old. Dive depth subsequently decreased to depths comparable to adult bearded seals (by the time pups were ~175 d old). Record maximum dive depth (368 m) and duration (16.5 min) were performed by pups that were 66 and 224 d old, respectively. Time spent hauled out decreased after weaning, with pups hauling out only sporadically after they were 75 d old. Bearded seal pups seem to be physiologically and behaviourally well developed by the time they are 2 mo old. Pups did not display the individually specialized diving behaviour seen in adults, which suggests that they continue to fine-tune their aquatic and other life-skills well past the end of the first year of life.

Preferred, small-scale foraging areas of two Southern Ocean fur seal species are not determined by habitat characteristics

BackgroundTo understand and predict the distribution of foragers, it is crucial to identify the factors that affect individual movement decisions at different scales. Individuals are expected to adjust their foraging movements to the hierarchical spatial distribution of resources. At a small local scale, spatial segregation in foraging habitat happens among individuals of closely situated colonies. If foraging segregation is due to differences in distribution of resources, we would expect segregated foraging areas to have divergent habitat characteristics.ResultsWe investigated how environmental characteristics of preferred foraging areas differ between two closely situated Subantarctic fur seal (Arctocephalus tropicalis) colonies and a single Antarctic fur seal (A. gazella) colony that forage in different pelagic areas even though they are located well within each other’s foraging range. We further investigated the influence of the seasonal cycle on those environmental factors. This study used tracking data from 121 adult female Subantarctic and Antarctic fur seals, collected during summer and winter (2009–2015), from three different colonies. Boosted Regression Tree species distribution models were used to determine key environmental variables associated with areas of fur seal restricted search behaviour. There were no differences in the relative influence of key environmental variables between colonies and seasons. The variables with the most influence for each colony and season were latitude, longitude and magnitude of sea-currents. The influence of latitude and longitude is a by-product of the species’ distinct foraging areas, despite the close proximity (< 25 km) of the colonies. The predicted potential foraging areas for each colony changed from summer to winter, reflecting the seasonal cycle of the Southern Ocean. The model predicted that the potential foraging areas of females from the three colonies should overlap, and the fact they do not in reality indicates that factors other than environmental are influencing the location of each colony’s foraging area.ConclusionsThe results indicated that small scale spatial segregation of foraging habitats is not driven by bottom-up processes. It is therefore important to also consider other potential drivers, e.g. competition, information transfer, and memory, to understand animal foraging decisions and movements.

Delayed effects of prey fish quality and winter temperature during the birth year on adult size and reproductive rate of Baltic grey seals

Environmental conditions of mammalian juveniles may have delayed effects on their life histories and fitness, such as body size or reproductive rate later in their lives. In the present study, we tested this hypothesis on Baltic grey seals (Halichoerus grypus) and examined (1) the possible effects of prey fish quality and winter temperature on body condition of grey seal pups of both sexes and (2) the possible delayed impacts of pup environment on the body size and birth rate of adult grey seals. Body condition (blubber thickness) of especially female pups in April–May correlated negatively with winter temperatures, and body condition of male pups correlated positively with prey fish quality (herring Clupea harengus and sprat Sprattus sprattus weight). Males reached the asymptotic length at the age of 10.3 years, and body length of adult males (≥ 10 years old) was positively related to herring and sprat weight in their birth year. Females reached the asymptotic length at the age of 5.9 years. Birth rate of females (age 7–24 years) was negatively related to winter temperature in their birth year. We conclude that both changes in prey fish quality and climate may affect body condition of pups and thus also cause delayed effects on adult fitness: body size and reproductive rate of Baltic grey seals.

Stalked barnacles on an adult male sub-Antarctic fur seal at Inaccessible Island, Tristan da Cunha

An adult male sub-Antarctic fur seal, Arctocephalus tropicalis, on Inaccessible Island in the Tristan da Cunha archipelago (TdC), was observed infested with goose barnacles, likely Lepas australis. Although adult females have been recorded to carry goose barnacles, this is the first record from an adult male at a breeding island. Males remain at sea throughout winter, so it is not clear why there are not more records of goose barnacles attached to their pelage.