Distribution and habitat suitability of Ross seals in a warming ocean

Understanding the determinants of poorly studied species’ spatial ecology is fundamental to understanding climate change impacts on those species and how to effectively prioritise their conservation. Ross seals (Ommatophoca rossii) are the least studied of the Antarctic pinnipeds with a limited knowledge of their spatial ecology. We present the largest tracking study for this species to date, create the first habitat models, and discuss the potential impacts of climate change on their preferred habitat and the implications for conservation. We combined newly collected satellite tracking data (2016–2019: n = 11) with previously published data (2001: n = 8) from the Weddell, King Haakon VII and Lazarev seas, Antarctica, and used 16 remotely sensed environmental variables to model Ross seal habitat suitability by means of boosted regression trees for summer and winter, respectively. Five of the top environmental predictors were relevant in both summer and winter (sea-surface temperature, distance to the ice edge, ice concentration standard deviation, mixed-layer depth, and sea-surface height anomalies). Ross seals preferred to forage in waters ranging between -1 and 2°C, where the mixed-layer depth was shallower in summer and deeper in winter, where current speeds were slower, and away from the ice edge in the open ocean. Receding ice edge and shoaling of the mixed layer induced by climate change may reduce swimming distances and diving depths, thereby reducing foraging costs. However, predicted increased current speeds and sea-surface temperatures may reduce habitat suitability in these regions. We suggest that the response of Ross seals to climate change will be regionally specific, their future success will ultimately depend on how their prey responds to regional climate effects and their own behavioural plasticity

Marine mammal hotspots across the circumpolar Arctic

Aim: Identify hotspots and areas of high species richness for Arctic marine mammals. Location: Circumpolar Arctic. Methods: A total of 2115 biologging devices were deployed on marine mammals from 13 species in the Arctic from 2005 to 2019. Getis-Ord Gi* hotspots were calculated based on the number of individuals in grid cells for each species and for phyloge-netic groups (nine pinnipeds, three cetaceans, all species) and areas with high spe-cies richness were identified for summer (Jun-Nov), winter (Dec-May) and the entire year. Seasonal habitat differences among species’ hotspots were investigated using Principal Component Analysis. Results: Hotspots and areas with high species richness occurred within the Arctic continental-shelf seas and within the marginal ice zone, particularly in the “Arctic gateways” of the north Atlantic and Pacific oceans. Summer hotspots were generally found further north than winter hotspots, but there were exceptions to this pattern, including bowhead whales in the Greenland-Barents Seas and species with coastal distributions in Svalbard, Norway and East Greenland. Areas with high species rich-ness generally overlapped high-density hotspots. Large regional and seasonal dif-ferences in habitat features of hotspots were found among species but also within species from different regions. Gap analysis (discrepancy between hotspots and IUCN ranges) identified species and regions where more research is required. Main conclusions: This study identified important areas (and habitat types) for Arctic marine mammals using available biotelemetry data. The results herein serve as a benchmark to measure future distributional shifts. Expanded monitoring and teleme-try studies are needed on Arctic species to understand the impacts of climate change and concomitant ecosystem changes (synergistic effects of multiple stressors). While efforts should be made to fill knowledge gaps, including regional gaps and more com-plete sex and age coverage, hotspots identified herein can inform management ef-forts to mitigate the impacts of human activities and ecological changes, including creation of protected areas

Gastroliths in the harp seal Phoca Groenlandica

An adult harp seal, caught by accident in a gill net during the peak of the seal invasions along the northern coasts of Norway (1986/87), was found to have eaten 2.466 kg of stones with masses up to 265 g. Different theories to why harp seals on occasion deliberately eat stones, with particular emphasis on the hypothesis that these may aid in the physical breakdown of fish flesh and hard fish bones, are discussed

Evidence of seawater drinking in fasting subadult hooded seals (Cystophora cristata)

The purpose of this study was to investigate the total water turnover rate of fasting subadult hooded seals in order to elucidate to what extent these animals rely in seawater drinking/mariposia at this life stage. Considering mariposia is important for later accurate estimations of food consumption using water turnover rate as a proxy. Five subadult hooded seals were kept fasting for 4 days in a seawater pool. Total body water (39.6 ± 2.5 % of total body mass) decreased by 3.1 ± 0.4 % of initial body water over the experimental period. Turnover rates were 16.7 ± 3.9 (influx) and 24.6 ± 4.6 (efflux) ml · dayˉ¹ · kgˉ¹ with a net water loss of 710 ± 51 ml · day-1. It was estimated that the seals drank approximately 947 ml of seawater per day, which corresponds to 61 % of total daily water influx. Initial body water was relatively low as a result of the high body fat (46.9 ± 3.2 % of initial body mass) shown in the animals. It is concluded that subadult fasting hooded seals drink significant amounts of seawater during fasting. Although mariposia stands out as the major source of free water in fasting hooded seals, the amount of seawater ingested is unlikely to provide a net gain of free water as it is provided by metabolic water. However, it may contribute to excrete the excess of urea produced during early phase I of fasting

Seasonal changes in background levels of deuterium and oxygen- 18 prove water drinking by harp seals, which affects the use of the doubly labelled water method

The aim of this study was to monitor seasonal changes in stable isotopes of pool freshwater and harp seal (Phoca groenlandica) body water, and to study whether these potential seasonal changes might bias results obtained using the doubly labelled water (DLW) method when measuring energy expenditure in animals with access to freshwater. Seasonal changes in the background levels of deuterium and oxygen-18 in the body water of four captive harp seals and in the freshwater pool in which they were kept were measured over a time period of 1 year. The seals were offered daily amounts of capelin and kept under a seasonal photoperiod of 69°N. Large seasonal variations of deuterium and oxygen-18 in the pool water were measured, and the isotope abundance in the body water showed similar seasonal changes to the pool water. This shows that the seals were continuously equilibrating with the surrounding water as a result of significant daily water drinking. Variations in background levels of deuterium and oxygen-18 in freshwater sources may be due to seasonal changes in physical processes such as precipitation and evaporation that cause fractionation of isotopes. Rapid and abrupt changes in the background levels of deuterium and oxygen-18 may complicate calculation of energy expenditure by use of the DLW method. It is therefore strongly recommended that analysis of seasonal changes in background levels of isotopes is performed before the DLW method is applied on (free-ranging) animals, and to use a control group in order to correct for changes in background levels

Hooded seal (Cystophora cristata) pups ingest snow and seawater during their post-weaning fast

The purpose of this study was to evaluate the importance of exogenous water intake (snow/seawater) in hooded seal (Cystophora cristata) pups during their postweaning fast. In this study, five hooded seal pups had ad lib access to snow and seawater for the first 12 and last 21 days of their post-weaning fast, respectively. Total body water and water flux were determined during both exposure periods by use of the tritiated water method. Blood samples were collected to monitor changes in hematocrit, plasma urea and plasma osmolality. Body mass loss was on average 0.36 kg day−1 . Average total body water changed from 15.7 to 11.4 L, while total water influx changed from 15 to 18 mL day−1 kg−1 during snow and seawater exposure, respectively. Of this influx an average of 35% can be attributed to metabolic water, while approximately 8% was due to respiratory water influx. Interestingly, 56 and 58% of the total water influx was due to snow and seawater ingestion, respectively, amounting to 8 mL day−1 kg−1 snow (counted as liquid water) and 10 mL day−1 kg−1 seawater. Based on the results of the plasma parameters it is concluded that fasting hooded seal pups maintain water balance and homeostasis when access to snow or seawater is permitted. It is further concluded that snow and seawater intake, in addition to metabolic and respiratory water, is important for maintenance of water balance and excretion of urea during the post-weaning fast of hooded seal pups

First record of plastic debris in the stomach of a hooded seal pup from the Greenland Sea

Plastic debris is globally found around the world and the remote Arctic is no exception. Arctic true seals are sentinel species of marine pollution and represent the link between marine food webs and Arctic apex predators like polar bears and humans. With regard to true seals, ingested macroplastics have never been reported in an Arctic species. We harvested 10 harp seals Pagophilus groenlandicus and 8 hooded seals Cystophora cristata from the breeding grounds in the pack ice of the Greenland Sea. The digestive tract was inspected exclusively for the presence of macroplastics (>5 mm). Two pieces of single-use plastic were found in the stomach of a weaned hooded seal pup. This study indicates that young Arctic marine predators may ingest macroplastics, and therefore may be at risk during their early stages of life due to human caused plastic pollution even in the remote Arctic pack ice

A life after Research? First Release of Harp Seals (Phoca groenlandica) after Temporary Captivity for Scientific Purposes

Three wild-caught female harp seals (Pagophilus groenlandicus) from the Greenland Sea stock were brought into temporary captivity in connection with a controlled validation study on energetics. The two pups and one adult were kept in two indoor and outdoor experimental facilities approved by the Norwegian Animal Research Authority. They were trained daily using operant conditioning to participate in experiments and husbandry and were regularly fed live fish. After 2.5 years, the harp seals were instrumented with satellite transmitters and released in the Barents Sea under a Norwegian Food Safety Authority permit. The tags transmitted for 45, 67, and 162 days for the juveniles and adult, respectively. The two juveniles remained in the Barents Sea east of the Svalbard Archipelago, while the adult female migrated to the Greenland Sea following a pattern consistent with that observed in wild harp seals from the same stock. They all performed regular deep dives (>100 m) and exhibited signs of foraging comparable to wild harp seals. Our results suggest that it is possible to conduct temporary captive studies with wild juvenile and adult harp seals. Study animals can be trained and subsequently released if they meet a set of criteria. This framework combines advantages of captive study design with traditional field methods and follows European ethical guidelines on animal experimentation with respect to the re-homing of experimentation animals

Ross seal tracking data from expeditions SCALE (MV SA Agulhas II, 2019), PS111 (RV Polarstern, 2018) and S55 (MV SA Agulhas II, 2016)

Ross seals (Ommatophoca rossii) were instrumented with satellite-linked position-temperature tags. Primary data were collected during spring and summer expeditions carried out by scientists of the Mammal Research Institute (MRI, University of Pretoria), South Africa, the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), Germany, and the UiT - The Arctic University of Norway (UiT). The expeditions were located north of the Lazarev Sea (SA Agulhas II Southern oCean seAsonaL Experiment Spring cruise, 2019) and in the eastern Weddell Sea and King Håkon VII Sea off Queen Maud Land (RV Polarstern PS111 expedition, 2018; SA Agulhas II SANAE 55 expedition, 2016), and combined with published data taken in the aforementioned region during the Norwegian Antarctic Research Expedition (NARE 2000/2001). Processing of the primary data followed an established workflow (2018, 2016) or is described in the source data set (Blix and Nordøy, 2007). The seals were captured along the ships' tracks and instrumented with Argos-linked (CLS, Toulouse, France) position-temperature tags (SPOT300s 2019 (n = 2), 2016 (4); SPLASH10-309A 2018 (2), 2016 (2); SPLASH9 2016 (1); or SDR-T16 (2000 n = 10) Wildlife Computers, Redmond, WA, USA) to investigate their ranging and foraging behaviour in the context of oceanographic features

Environmental drivers of population-level variation in the migratory and diving ontogeny of an Arctic top predator

The development of migratory strategies that enable juveniles to survive to sexual maturity is critical for species that exploit seasonal niches. For animals that forage via breath-hold diving, this requires a combination of both physiological and foraging skill development. Here, we assess how migratory and dive behaviour develop over the first year of life for a migratory Arctic top predator, the harp seal Pagophilus groenlandicus, tracked using animal-borne satellite relay data loggers. We reveal similarities in migratory movements and differences in diving behaviour between 38 juveniles tracked from the Greenland Sea and Northwest Atlantic breeding populations. In both regions, periods of resident and transitory behaviour during migration were associated with proxies for food availability: sea ice concentration and bathymetric depth. However, while ontogenetic development of dive behaviour was similar for both populations of juveniles over the first 25 days, after this time Greenland Sea animals performed shorter and shallower dives and were more closely associated with sea ice than Northwest Atlantic animals. Together, these results highlight the role of both intrinsic and extrinsic factors in shaping early life behaviour. Variation in the environmental conditions experienced during early life may shape how different populations respond to the rapid changes occurring in the Arctic ocean ecosystem