Multi-state mark-recapture models as a novel approach to estimate factors affecting attendance patterns of lactating subantarctic fur seals from Marion Island

Observer-based studies often underestimate key ecological parameters. Here a fresh approach was used to analyse six years (2006–11) of attendance cycles to estimate foraging trip lengths of a lactating flipper-tagged otariid: subantarctic fur seals at Marion Island. Multi-state mark-recapture models were used to calculate detection failures of females, correct estimates accordingly, and investigate the effects of year, season, pup sex and the presence of a telemetry device on attendance cycle parameters. There were no differences between corrected and uncorrected attendance data. This is attributed to the high capture probability across all seasons (range: 83–98%). This illustrates that observer-based studies are useful to augment telemetry studies. Only season and pup sex had a significant impact on female provisioning rates. In winter, foraging trip durations were longer (t-value = 25.22, P <0.0001) and attendance durations shorter (t-value = -2.15, P = 0.01) than during summer. Females with female pups spent a higher proportion of their time on land (χ2 = 6.6, P < 0.05). Male pups have higher growth demands and are larger which suggests they can deplete female milk-stores faster.Department of Science and Technology,through the National Research Foundation (NRF), in support of the Marion Island Marine Mammal Programme (MIMMP) of the MRI.http://journals.cambridge.org/action/displayJournal?jid=ANS2015-12-31hb201

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

High-resolution satellite imagery meets the challenge of monitoring remote marine protected areas in the Antarctic and beyond

Remote, high-latitude oceans can prove challenging for the designation and implementation of marine protected areas (MPAs), partly due to issues in monitoring inaccessible localities and large spatial scales. A lack of protection combined with damage from growing human activities has contributed to the degradation of some of the Earth’s richest marine biodiversity and highlights the urgent need to support improved marine conservation. High-resolution satellite imagery (VHR; 0.3–0.6 m spatial resolution) provides a much-needed tool for monitoring sentinel species in remote oceans, which would strengthen current and future MPA research and monitoring programs across the globe. This perspective specifies how recent advances in VHR studies have contributed to knowledge regarding occurrence, habitat suitability, and abundance of mesopredators in the Southern Ocean. We demonstrate how knowledge gained through VHR offers a cost-effective and easily accessible method for collecting previously unobtainable data to inform a representative network of Southern Ocean MPAs, and how the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) could utilize this technology. As VHR and automated detection algorithms continue to improve, we showcase a promising opportunity to use these methods to complement current research and monitoring efforts, thus strengthening MPA efforts in the Southern Ocean and beyond.https://wileyonlinelibrary.com/journal/conlam2023Zoology and Entomolog

Ross seal distribution in the Weddell Sea : fact and fallacy

The presence of Ross seals (Ommatophoca rossii) throughout the Weddell Sea is at best equivocal although overview articles usually depict this as fact on distribution maps. This study reviewed the appropriate literature on the distribution of Ross seals in the Weddell Sea sensu lato and investigated their presence/absence during two expeditions (summer/autumn of 2014 and 2018) into its most southern reaches off the Filchner-Ronne Ice Shelf. Both ship-board and helicopter surveys were done primarily along the eastern aspect and the south-western limit of the Weddell Sea. Evidence suggests that Ross seals are absent from the Weddell Sea during winter, utilizing the northernmost fringes of the pack-ice during the spring breeding (pupping and mating) season. Ross seals are absent from the inner reaches of the Weddell Sea past about 73° S in summer and early autumn when they occur in number in the eastern Weddell Sea eastwards from about 30° W longitude.The Department of Science and Technology (DST) through the National Research Foundation (NRF).http://link.springer.com/journal/3002020-12-02hj2020Mammal Research InstituteZoology and Entomolog

Return customers: foraging site fidelity and the effect of environmental variability in wide-ranging Antarctic fur seals

Strategies employed by wide-ranging foraging animals involve consideration of habitat quality and predictability and should maximise net energy gain. Fidelity to foraging sites is common in areas of high resource availability or where predictable changes in resource availability occur. However, if resource availability is heterogeneous or unpredictable, as it often is in marine environments, then habitat familiarity may also present ecological benefits to individuals. We examined the winter foraging distribution of female Antarctic fur seals, Arctocephalus gazelle, over four years to assess the degree of foraging site fidelity at two scales; within and between years. On average, between-year fidelity was strong, with most individuals utilising more than half of their annual foraging home range over multiple years. However, fidelity was a bimodal strategy among individuals, with five out of eight animals recording between-year overlap values of greater than 50%, while three animals recorded values of less than 5%. High long-term variance in sea surface temperature, a potential proxy for elevated long-term productivity and prey availability, typified areas of overlap. Within-year foraging site fidelity was weak, indicating that successive trips over the winter target different geographic areas. We suggest that over a season, changes in prey availability are predictable enough for individuals to shift foraging area in response, with limited associated energetic costs. Conversely, over multiple years, the availability of prey resources is less spatially and temporally predictable, increasing the potential costs of shifting foraging area and favouring long-term site fidelity. In a dynamic and patchy environment, multi-year foraging site fidelity may confer a long-term energetic advantage to the individual. Such behaviours that operate at the individual level have evolutionary and ecological implications and are potential drivers of niche specialization and modifiers of intra-specific competition

Geographic variation in subantarctic fur seal pup growth : linkages with environmental variability and population density

Marine predator populations are sensitive to temporal variation in prey availability, but prey dynamics are often difficult to quantify. Long-term measures of offspring growth is a useful performance attribute to gauge the potential demographic direction for such predator populations, especially where other metrics (e.g., population size estimates) are lacking. Subantarctic fur seal (Arctocephalus tropicalis) females are central place foragers during a protracted lactation period, and their foraging success determines the growth and vitality of their offspring. Using data spanning over 2 decades, we assessed geographic and temporal variation in growth rates and weaning mass of subantarctic fur seal pups at 2 of the species’ principal populations (Gough and Marion islands) and identified environmental conditions that may, through assumed bottom-up mechanisms, affect body mass at weaning. While Marion Island pups grew at an average rate of between 0.040 and 0.067kg/day early in lactation (comparable to conspecific growth at Amsterdam Island), the mean growth rate at Gough Island (approximately 0.030kg/day) was lower than the growth rate represented by the bottom 5% of the body mass distribution at Marion Island. Notwithstanding substantial interannual variability, we found support for a negative trend in weaning mass at both populations, suggesting a rise in limiting factors that is hypothesized to relate to concurrent local population size increases. Weaning mass tended to be higher when sea surface temperatures were warmer (with a stronger positive effect at Gough Island) and during positive phases of the Southern Oscillation Index (La Niña events), with a stronger positive effect in males. Given the low weaning mass of Gough Island fur seal pups, continued population growth here seems unlikely. While density-dependent regulation appears to have increased in strength at Marion Island, terminating rapid population growth, current weaning weights remain above the physiological limits of growth in subantarctic fur sealshttp://jmammal.oxfordjournals.org2017-04-30hb2016Mammal Research InstituteZoology and Entomolog

Oedipus complex in an Antarctic fur seal pup?

We present the first evidence of a possible case of the Oedipus complex in a nonprimate. An Antarctic fur seal pup, Arctocephalus gazella, unsuccessfully directed what appeared to be copulatory behaviour towards its own mother on several occasions. A herding sub-adult bull chased the pup from the female, which strengthens our suggestion that it was copulatory behaviour we witnessed. This seemed to constitute innocent sexual play with elements of the Oedipus complex rather than coercion because the female was not stressed nor did the pup possess the physical strength to coerce the female.The Department of Science and Technology, through the National Research Foundation (South Africa), provided financial support.http://www.springer.com/life+sci/zoology/journal/1016

Cross-seasonal foraging site fidelity of subantarctic fur seals : implications for marine conservation areas

Marine top-predators show fidelity to foraging areas with predictable high-quality food patches. Areas of predictable prey yield are of conservation importance and telemetry data aid in identifying such areas. This study examined colony specific and intra-individual foraging site fidelity of lactating Subantarctic fur seals (Arctocephalus tropicalis) from Marion Island (46°54‟S, 37°45‟E) during summer and winter, comparing commitment to foraging areas across seasons. Thirty-one females were tracked in 2009-2013 resulting in 111 foraging trips for analyses. Inter-annually, preferred foraging areas in summer were consistently ≈200 km due east of Marion Island towards the Gallieni Rise. Summer individuals' core utilization areas overlapped by an estimated 32.84% (CI: 24.53% - 41.94%). Seals responded to a decrease in regional productivity in winter by foraging in more distant alternative areas. In winter, individuals changed their travelling direction to north-east of Marion Island and foraged further afield, around the Del Caño Rise and along the South-west Indian Ridge. Despite preferring some foraging areas in winter, there was a low amount of overlap 6.03% (CI 4.02% - 9.16%) of individual core utilization areas. The foraging grounds identified in this study have not been included in prior conservation assessments and are important in conserving for this globally significant, and currently declining, population of Subantarctic fur seals and perhaps other toppredators breeding at Marion Island as well. Differences between winter and summer preferred foraging areas highlight the importance of sampling during different seasons when using telemetry data for the identification of potential pelagic conservation areas.The Department of Science and Technology, through the National Research Foundation (NRF), in support of the Marion Island Marine Mammal Programme of the Mammal Research Institute.http://www.int-res.com2017-07-31hb2016Zoology and Entomolog

First confirmed record of a leucistic Antarctic fur seal pup born outside the Scotia Arc Islands

A leucistic Antarctic fur seal (Arctocephalus gazella) pup was born on subantarctic Marion Island during the austral summer of 2010/2011. This is the first confirmed record of a leucistic fur seal pup born outside the Scotia Arc islands. Additionally, we report on a leucistic adult female Antarctic fur seal producing typical black pups for five non-consecutive summers on Marion Island. The birth of a leucistic pup, together with the multiple black pups produced by the leucistic female, suggests that the recessive genes responsible for leucism are now entrenched within the Marion Island population.Department of Science and Technology, through the National Research Foundation (South Africa).http://link.springer.com/journal/3002016-04-30hb201

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.The National Research Foundation (NRF) South African National Antarctic Programme (SANAP) and the Open Access Publication Funds of Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung.https://www.frontiersin.org/journals/marine-science#am2022Mammal Research InstituteZoology and Entomolog