Speakman, Cassie, Hoskins, AJ, Hindell, MA, Costa, DP, Hartog, JR, Hobday, AJ, Arnould, John, Speakman, Cassie, Hoskins, AJ, Hindell, MA, Costa, DP, Hartog, JR, Hobday, AJ, and Arnould, John
Hooker, Sascha K, Andrews, Russel D, Arnould, John PY, Bester, Marthán N, Davis, Randall W, Insley, Stephen J, Gales, Nick J, Goldsworthy, Simon D, McKnight, J Chris, Hooker, Sascha K, Andrews, Russel D, Arnould, John PY, Bester, Marthán N, Davis, Randall W, Insley, Stephen J, Gales, Nick J, Goldsworthy, Simon D, and McKnight, J Chris
Management of gases during diving is not well understood across marine mammal species. Prior to diving, phocid (true) seals generally exhale, a behaviour thought to assist with the prevention of decompression sickness. Otariid seals (fur seals and sea lions) have a greater reliance on their lung oxygen stores, and inhale prior to diving. One otariid, the Antarctic fur seal (Arctocephalus gazella), then exhales during the final 50–85% of the return to the surface, which may prevent another gas management issue: shallow-water blackout. Here, we compare data collected from animal-attached tags (video cameras, hydrophones and conductivity sensors) deployed on a suite of otariid seal species to examine the ubiquity of ascent exhalations for this group. We find evidence for ascent exhalations across four fur seal species, but that such exhalations are absent for three sea lion species. Fur seals and sea lions are no longer genetically separated into distinct subfamilies, but are morphologically distinguished by the thick underfur layer of fur seals. Together with their smaller size and energetic dives, we suggest their air-filled fur might underlie the need to perform these exhalations, although whether to reduce buoyancy and ascent speed, for the avoidance of shallow-water blackout or to prevent other cardiovascular management issues in their diving remains unclear. This article is part of the theme issue ‘Measuring physiology in free-living animals (Part I)’.
Speakman, Cassie, Hoskins, AJ, Hindell, MA, Costa, DP, Hartog, JR, Hobday, AJ, Arnould, John, Speakman, Cassie, Hoskins, AJ, Hindell, MA, Costa, DP, Hartog, JR, Hobday, AJ, and Arnould, John
McHuron, Elizabeth, McHuron, Elizabeth, Sterling, Jeremy, Costa, Daniel, Goebel, Michael, McHuron, Elizabeth, McHuron, Elizabeth, Sterling, Jeremy, Costa, Daniel, and Goebel, Michael
Quantifying metabolic rates and the factors that influence them is key to wildlife conservation efforts because anthropogenic activities and habitat alteration can disrupt energy balance, which is critical for reproduction and survival. We investigated the effect of diving behaviour, diet and season on field metabolic rates (FMR) and foraging success of lactating northern fur seals (Callorhinus ursinus) from the Pribilof Islands during a period of population decline. Variation in at-sea FMR was in part explained by season and trip duration, with values that ranged from 5.18 to 9.68 W kg-1 (n = 48). Fur seals experienced a 7.2% increase in at-sea FMR from summer to fall and a 1.9% decrease in at-sea FMR for each additional day spent at sea. There was no effect of foraging effort, dive depth or diet on at-sea FMR. Mass gains increased with trip duration and were greater in the fall compared with summer, but were unrelated to at-sea FMR, diving behaviour and diet. Seasonal increases in at-sea FMR may have been due to costs associated with the annual molt but did not appear to adversely impact the ability of females to gain mass on foraging trips. The overall high metabolic rates in conjunction with the lack of any diet-related effects on at-sea FMR suggests that northern fur seals may have reached a metabolic ceiling early in the population decline. This provides indirect evidence that food limitation may be contributing to the low pup growth rates observed in the Pribilof Islands, as a high metabolic overhead likely results in less available energy for lactation. The limited ability of female fur seals to cope with changes in prey availability through physiological mechanisms is particularly concerning given the recent and unprecedented environmental changes in the Bering Sea that are predicted to have ecosystem-level impacts.
McHuron, EA, McHuron, EA, Walcott, SM, Zeligs, J, Skrovan, S, Costa, DP, Reichmuth, C, McHuron, EA, McHuron, EA, Walcott, SM, Zeligs, J, Skrovan, S, Costa, DP, and Reichmuth, C
McHuron, EA, McHuron, EA, Walcott, SM, Zeligs, J, Skrovan, S, Costa, DP, Reichmuth, C, McHuron, EA, McHuron, EA, Walcott, SM, Zeligs, J, Skrovan, S, Costa, DP, and Reichmuth, C
Lynch, Michael, Kirkwood, Roger, Mitchell, Anthony, Duignan, Padraig, Arnould, John P. Y., Lynch, Michael, Kirkwood, Roger, Mitchell, Anthony, Duignan, Padraig, and Arnould, John P. Y.
Gibbens, John, Parry, Laura J., Arnould, John P. Y, Gibbens, John, Parry, Laura J., and Arnould, John P. Y
Recovery of the Australian fur seal (Arctocephalus pusillus doriferus) population has been slower than that of other fur seals, perhaps due to nutritional constraints on fecundity. However, the population doubled in recent decades, suggesting that reproductive rates may have changed. Pregnancy rates and birthrates were estimated and the influences of maternal age, size, condition, and lactation status were investigated over 3 consecutive breeding seasons (2003–2005). Mid-gestation pregnancy rate, estimated from plasma progesterone concentrations, was 84% ± 3% (mean ± SE) and was negatively influenced only by age (P< 0.001). Birthrate, estimated from observations of females with newborn offspring during the breeding season, was 53% 6 3% (mean ± SE) and was influenced negatively by lactation status (P = 0.035). The difference between pregnancy rates and birthrates suggests that a high degree of late-gestation abortion occurs, especially in younger females. Lactation status was not influenced by any variables, and the high rate (86% ± 2%; mean ± SE) suggests that many offspring are suckled beyond the typical weaning period. Although relationships between reproductive rates and body condition were not found, the results are consistent with a nutritional stress hypothesis. The recent increase in population growth is not due to increased fecundity, which remains low compared to other otariids. Paradoxically, high pregnancy rates were observed in young females (3 years), suggesting that rapid maturity is adaptive for benthic foragers.
de Bruyn, P.J.Nico., Tosh, Cheryl A., Oosthuizen, W. Chris., Bester, Marthán N., Arnould, John P.Y, de Bruyn, P.J.Nico., Tosh, Cheryl A., Oosthuizen, W. Chris., Bester, Marthán N., and Arnould, John P.Y
Sixteen lactating subantarctic fur seals Arctocephalus tropicalis were satellite-tracked during the winter of 2006 (n = 6), summer of 2006/07 (n = 6) and autumn/winter (n = 4) of 2007, from Marion Island, Southern Ocean. Despite varied individual movement patterns, a favoured foraging area lay to the northeast of the island. In contrast to findings for populations at similar latitudes, seals from Marion Island did not undertake short overnight foraging trips, but trips consistently went beyond 300 km from the island. This aligns with the at-sea duration of lactating seals’ foraging trips from temperate Amsterdam Island, but differs from subantarctic Crozet and Macquarie islands. Time spent at sea, maximum distances travelled and movement variation of tracks from the island varied seasonally. Faecal analysis suggests the diet comprised primarily myctophid fish with limited seasonal variation. Well-defined areas of restricted movement coincided with significant bathymetric features to the west/northwest of the Crozet Plateau, with the Del Caño Rise clearly being important. Positive and negative sea-surface height anomalies (compared to the mean) appeared to be preferred by most seals across seasons. Higher summer sea-surface temperatures correlated with the movements of some seals. Higher chlorophyll a concentrations dictated transit and foraging areas during summer. Bathymetrically influenced oceanographic variables likely explain these preferred long-distance eastward movements. The Îles Crozet and Marion island subantarctic fur seals differ in their foraging ecology despite being neighbours. Conversely, the subantarctic fur seal populations from the distant Amsterdam and Marion islands appear to be similarly influenced by such environmental factors.
Kuhn, Carey E., Kuhn, Carey E., Kuhn, Carey E., and Kuhn, Carey E.
Pinniped have evolved a range of reproductive and foraging patterns to deal with the constraint of terrestrial parturition and marine feeding. To understand the link between these constraints it is necessary to understand both reproductive periods on land and foraging at sea. I examined the foraging behavior of a phocid (northern elephant seal, Mirounga angustirostris) and otariid (California sea lion, Zalophus californianus) species to provide insight into the divergent life histories of these families. To understand foraging behavior it is necessary to know when and where animals find prey. Using stomach temperature telemetry, I conducted rigorous feeding experiments with both species to determine whether measures of stomach temperature can be used to identify and quantify prey consumption. Feedings were identified with high accuracy and the equations to estimate mass consumed were not significantly different between species.Until recently, studies on the foraging behavior of marine predators have relied on indirect measures of feeding, such as changes in diving behavior or movement patterns. When combined with measures of at sea behavior, stomach temperature telemetry can provide information about when and where animals uccessfully capture prey. I deployed stomach temperature telemeters along with time-depth recorders and satellite transmitters to examine the foraging behavior of northern elephant seals. This resulted in the first measures of feeding behavior and foraging success in elephant seals, as well as provided a validation of indirect indices of foraging behavior.Finally, I examined the foraging behavior of free-ranging California sea lions and documented how their behavior changed annually in response to environmental variation that occurred over three years. Although stomach temperature telemeters were deployed on sea lions, I was only able to maintain the telemeters in the animals for long enough to measure at sea feeding in one female. Therefore, fora
Kuhn, Carey E., Kuhn, Carey E., Kuhn, Carey E., and Kuhn, Carey E.
Pinniped have evolved a range of reproductive and foraging patterns to deal with the constraint of terrestrial parturition and marine feeding. To understand the link between these constraints it is necessary to understand both reproductive periods on land and foraging at sea. I examined the foraging behavior of a phocid (northern elephant seal, Mirounga angustirostris) and otariid (California sea lion, Zalophus californianus) species to provide insight into the divergent life histories of these families. To understand foraging behavior it is necessary to know when and where animals find prey. Using stomach temperature telemetry, I conducted rigorous feeding experiments with both species to determine whether measures of stomach temperature can be used to identify and quantify prey consumption. Feedings were identified with high accuracy and the equations to estimate mass consumed were not significantly different between species.Until recently, studies on the foraging behavior of marine predators have relied on indirect measures of feeding, such as changes in diving behavior or movement patterns. When combined with measures of at sea behavior, stomach temperature telemetry can provide information about when and where animals uccessfully capture prey. I deployed stomach temperature telemeters along with time-depth recorders and satellite transmitters to examine the foraging behavior of northern elephant seals. This resulted in the first measures of feeding behavior and foraging success in elephant seals, as well as provided a validation of indirect indices of foraging behavior.Finally, I examined the foraging behavior of free-ranging California sea lions and documented how their behavior changed annually in response to environmental variation that occurred over three years. Although stomach temperature telemeters were deployed on sea lions, I was only able to maintain the telemeters in the animals for long enough to measure at sea feeding in one female. Therefore, fora
Hooker, Sascha K., Miller, Patrick J. O., Johnson, Mark P., Cox, Oliver P., Boyd, Ian L., Hooker, Sascha K., Miller, Patrick J. O., Johnson, Mark P., Cox, Oliver P., and Boyd, Ian L.
Author Posting. © Royal Society, 2005. This article is posted here by permission of Royal Society for personal use, not for redistribution. The definitive version was published in Proceedings of the Royal Society of London B 272 (2005): 355-363, doi:10.1098/rspb.2004.2964., Novel observations collected from video, acoustic and conductivity sensors showed that Antarctic fur seals consistently exhale during the last 50–85% of ascent from all dives (10–160 m, n > 8000 dives from 50 seals). The depth of initial bubble emission was best predicted by maximum dive depth, suggesting an underlying physical mechanism. Bubble sound intensity recorded from one seal followed predictions of a simple model based on venting expanding lung air with decreasing pressure. Comparison of air release between dives, together with lack of variation in intensity of thrusting movement during initial descent regardless of ultimate dive depth, suggested that inhaled diving lung volume was constant for all dives. The thrusting intensity in the final phase of ascent was greater for dives in which ascent exhalation began at a greater depth, suggesting an energetic cost to this behaviour, probably as a result of loss of buoyancy from reduced lung volume. These results suggest that fur seals descend with full lung air stores, and thus face the physiological consequences of pressure at depth. We suggest that these regular and predictable ascent exhalations could function to reduce the potential for a precipitous drop in blood oxygen that would result in shallow-water blackout., S.K.H. received support from a Royal Society Dorothy Hodgkin fellowship; P.J.O.M. received support from a Royal Society USA fellowship.
Hooker, Sascha K., Miller, Patrick J. O., Johnson, Mark P., Cox, Oliver P., Boyd, Ian L., Hooker, Sascha K., Miller, Patrick J. O., Johnson, Mark P., Cox, Oliver P., and Boyd, Ian L.
Author Posting. © Royal Society, 2005. This article is posted here by permission of Royal Society for personal use, not for redistribution. The definitive version was published in Proceedings of the Royal Society of London B 272 (2005): 355-363, doi:10.1098/rspb.2004.2964., Novel observations collected from video, acoustic and conductivity sensors showed that Antarctic fur seals consistently exhale during the last 50–85% of ascent from all dives (10–160 m, n > 8000 dives from 50 seals). The depth of initial bubble emission was best predicted by maximum dive depth, suggesting an underlying physical mechanism. Bubble sound intensity recorded from one seal followed predictions of a simple model based on venting expanding lung air with decreasing pressure. Comparison of air release between dives, together with lack of variation in intensity of thrusting movement during initial descent regardless of ultimate dive depth, suggested that inhaled diving lung volume was constant for all dives. The thrusting intensity in the final phase of ascent was greater for dives in which ascent exhalation began at a greater depth, suggesting an energetic cost to this behaviour, probably as a result of loss of buoyancy from reduced lung volume. These results suggest that fur seals descend with full lung air stores, and thus face the physiological consequences of pressure at depth. We suggest that these regular and predictable ascent exhalations could function to reduce the potential for a precipitous drop in blood oxygen that would result in shallow-water blackout., S.K.H. received support from a Royal Society Dorothy Hodgkin fellowship; P.J.O.M. received support from a Royal Society USA fellowship.
Hooker, Sascha K., Miller, Patrick J. O., Johnson, Mark P., Cox, Oliver P., Boyd, Ian L., Hooker, Sascha K., Miller, Patrick J. O., Johnson, Mark P., Cox, Oliver P., and Boyd, Ian L.
Author Posting. © Royal Society, 2005. This article is posted here by permission of Royal Society for personal use, not for redistribution. The definitive version was published in Proceedings of the Royal Society of London B 272 (2005): 355-363, doi:10.1098/rspb.2004.2964., Novel observations collected from video, acoustic and conductivity sensors showed that Antarctic fur seals consistently exhale during the last 50–85% of ascent from all dives (10–160 m, n > 8000 dives from 50 seals). The depth of initial bubble emission was best predicted by maximum dive depth, suggesting an underlying physical mechanism. Bubble sound intensity recorded from one seal followed predictions of a simple model based on venting expanding lung air with decreasing pressure. Comparison of air release between dives, together with lack of variation in intensity of thrusting movement during initial descent regardless of ultimate dive depth, suggested that inhaled diving lung volume was constant for all dives. The thrusting intensity in the final phase of ascent was greater for dives in which ascent exhalation began at a greater depth, suggesting an energetic cost to this behaviour, probably as a result of loss of buoyancy from reduced lung volume. These results suggest that fur seals descend with full lung air stores, and thus face the physiological consequences of pressure at depth. We suggest that these regular and predictable ascent exhalations could function to reduce the potential for a precipitous drop in blood oxygen that would result in shallow-water blackout., S.K.H. received support from a Royal Society Dorothy Hodgkin fellowship; P.J.O.M. received support from a Royal Society USA fellowship.
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