Implantation of subcutaneous heart rate data loggers in southern elephant seals (Mirounga leonina)

Unlike most phocid species (Phocidae), Mirounga leonina (southern elephant seals) experience a catastrophic moult where they not only replace their hair but also their epidermis when ashore for approximately 1 month. Few studies have investigated behavioural and physiological adaptations of southern elephant seals during the moult fast, a particularly energetically costly life cycle’s phase. Recording heart rate is a reliable technique for estimating energy expenditure in the field. For the first time, subcutaneous heart rate data loggers were successfully implanted during the moult in two free-ranging southern elephant seals over 3–6 days. No substantial postoperative complications were encountered and consistent heart rate data were obtained. This promising surgical technique opens new opportunities for monitoring heart rate in phocid seals

Environmental and physiological determinants of huddling behavior of molting female southern elephant seals (Mirounga leonina)

The overall study was funded by the IPEV (Program 1037 HEnergES), doctoral fellowships of French Ministry of Higher Education and Research, the University of St Andrews, the Marine Alliance for Science and Technology for Scotland (MASTS) and the Carnegie Trust for the Universities of Scotland.While endotherms can rely on their insulation to reduce heat loss to adapt to cold environments, renewing of fur during molt impairs insulation while they have to perfuse the periphery to support epidermal tissues. The southern elephant seal Mirounga leonina undertakes an annual catastrophic molt while fasting on land in a wet, windy and cold environment. However, southern elephant seals show characteristic aggregation patterns that are predicted to reduce high metabolic costs during the molt. Between 2012 and 2016, 59 female elephant seals were tracked on land during their molt to study their aggregation behavior in relation to molt stage, habitat type and local weather conditions. Infrared thermography and stomach temperature loggers were used to observe variation in body surface and internal temperature in relation to molt stage and aggregation behavior. We found that thermal constraints varied during the molt, with a peak in surface temperature during the mid-stage of the molt. Wallows (mud pools) appear as favorable habitat to aggregate while molting. Indeed, wallows offered a warmer microclimate with greater ground temperature and lower wind speed. Moreover, there was a greater proportion of aggregated seals and larger group size in wallows. These aggregation patterns in wallows were influenced by local weather such that a greater proportion of seals were located in the center of the aggregation, and larger group size occurred during days of unfavorable meteorological conditions. We also observed a higher proportion of seals at mid-stage of molt amongst aggregated seals compared to isolated individuals. This aggregation behavior may reduce the cost of thermogenesis as surface body temperature and stomach temperature were cooler by 1.0 °C and 1.5 °C, respectively, in aggregated compared to isolated seals. As a consequence, huddling behavior may be thermally advantageous for female southern elephant seals during the molt.PostprintPeer reviewe

Metabolic heat loss in southern elephant seals (Mirounga leonina) differs with stage of moult and between habitats

The moult in southern elephant seals (Mirounga leonina) represents an especially energetically demanding period during which seals must maintain high skin temperature to facilitate complete replacement of body fur and upper dermis. In this study, heat flux from the body surface was measured on 18 moulting southern elephant seals to estimate metabolic heat loss in three different habitats (beach, wallow and vegetation). Temperature data loggers were also deployed on 10 southern elephant seals to monitor skin surface temperature. On average, heat loss of animals on the beach was greater than in wallows or vegetation, and greater in wallows than in vegetation. Heat loss across all habitats during the moult equated to 1.8 x resting metabolic rate (RMR). The greatest heat loss of animals was recorded in the beach habitat during the late moult, that represented 2.3 x RMR. Mass loss was 3.6 ± 0.3 kg day-1, resulting in changes in body condition as the moult progressed. As body condition declined, skin surface temperature also decreased, suggesting that as animals approached the end of the moult blood flow to the skin surface was no longer required for hair growth

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

The overall study was funded by the Institut Polaire Français Paul-Emile Victor (IPEV program 1037 HEnergES), doctoral fellowships of French Ministry of Higher Education and Research, the University of St Andrews, the Marine Alliance for Science and Technology for Scotland (MASTS), and the Carnegie Trust for the Universities of Scotland.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.Publisher PDFPeer reviewe

Weather_Quadrat

Meteorological variables including air temperature (°C), relative humidity (%), wind speed (m/s) and solar radiation (W/m²) measured at the start of each quadrat Q' count

Weather_Station

Daily mean air temperature (°C), relative humidity (%), wind speed (m/s), solar radiation (W/m²) and daily total precipitation recorded by the automatic weather station in Pointe Suzanne (Kerguelen) during field sessions between 2012 and 2016. Dates were selected to correspond to GPS loggers records

Individual_Data

Individual data collection of 60 females captured, weighed, measured, equipped (GPS), monitored (daily observations of habitat use, huddling and hair shedding) and recaptured during their moult in Kerguelen (colony of Pointe Suzanne) between 2012 and 2016. Individual rate of habitat use and aggregation rate were calculated for individuals observed at least 3 times each

GPS_Data

Retrieved GPS loggers raw data (latitude and longitude records) for each 23 individuals equipped and monitored during their molt in the field in Kerguelen (colony of Pointe Suzanne) between 2012 and 2016

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

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