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Predators affect prey through mortality, and prey respond by employing antipredatory strategies. Although leatherback sea turtles Dermochelys coriacea are the largest sea turtle, they are susceptible to shark predation. Females lay multiple clutches of eggs separated by a ~10 d internesting interval at sea, during which they move many kilometers away from the nesting beach. The goal of this study was to test the hypothesis that this wide-ranging behavior was associated with predator avoidance. To accomplish this goal, we used animal-borne video and data recorders along with satellite telemetry to monitor diving behavior and track the at-sea movements of females during the internesting intervals on St. Croix, US Virgin Islands. After they departed the nesting beach, females immediately swam a mean maximum distance of 101 km from St. Croix. The mean transit distance during 10.19 d at sea was 466 km. We recorded 102 periods during which females inverted and rotated vigorously for an average of 2.7 min at or near the surface. Because females nesting on St. Croix commonly exhibit scars and fresh wounds, many of which result from shark encounters, this behavior likely represents a defensive response to predator attack. The frequency of defensive behaviors that occurred -1) was 3.3-fold greater than when they were >6 km from shore (1.4 d-1). By moving offshore, females reduced the possibility of predator encounters by 53%.

Weddell seals (Leptonychotes weddellii) are well adapted to the fast-ice environment of Antarctica, where the majority of their activities are conducted underwater. Little is known about their capacity for terrestrial movement. During a study of their underwater homing ability, we also tracked the on-ice movements of six Weddell seals that had been displaced approximately 10 km from their capture locations along the southwestern coast of Ross Island, Antarctica. Each seal was instrumented with a satellite tag and released into one of the three isolated breathing holes. After at least 2 days in the water, the seal hauled out and traveled freely across the sea ice at a mean rate of 4.4 (± 2.4) km d−1 (maximum 8.3 km d−1). Travel headings, computed from GPS, and Argos positions after seals had traveled 2.1 to 7.5 km, revealed that all seals traveled along remarkably straight paths. Not all seals traveled the same heading, but each seal that was released more than once moved along the same heading, regardless of release location. Most headings traveled by seals were in line with prominent geographic features having high visual contrast, but some seals traveled consistently in directions with no visible landmarks, and other seals moved along their preferred heading during periods when bad weather obscured visual landmarks. These initial data indicate directed terrestrial movement by Weddell seals and invite further studies of the cues they use to maintain consistent headings.

Keeping warm when small Several mammal species live in cold-water environments, enabled by adaptations such as blubber and large size. A notable exception to this rule is the sea otter, a species that is orders of magnitude smaller and skinnier than the others. It is known that the sea otter's unusually thick fur helps, but Wright et al. show that they are also internally warmed by thermogenic leak from skeletal muscle, a process that elevates their metabolic rate three times above that expected for their size. This mechanism is present even in infants with immature muscles, providing these animals with internal warmth from birth. Science , abf4557, this issue p. 223

Many agencies provided funding and logistical support for the various research efforts resulting in the data presented here: the South African Department of Science and Technology, administered by the National Research Foundation and the Department of Environmental Affairs for subantarctic fur seal work; the Australian Research Council (DP110102065), Holsworth Wildlife Research Endowment and the Office of Naval Research (Marine Mammals and Biological Oceanography Program Award no. N00014-10-1-0385) for Australian fur seal work; the National Oceanic and Atmospheric Administration (NOAA) via grants to the Alaska SeaLife Center and the National Marine Mammal Laboratory, with additional funding and logistical support from North Pacific Wildlife Consulting for Steller sea lion and northern fur seal (Russia) work; the National Marine Mammal Laboratory, National Marine Fisheries Service, NOAA for northern fur seal (Alaska) work. Research support for R.W. Davis was provided by the National Science Foundation. 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. Postprint Postprint

International audience; Elephant seals, Mirounga spp., are highly dimorphic, having different energetic requirements according to age and sex, and foraging in various ecological and oceanographic contexts. Resource partitioning has been shown for the sub‐Antarctic populations of southern elephant seals, M. leonina, where colonies are surrounded by narrow shelves that deepen abruptly. In contrast, seals from Península Valdés (Argentina), in the northernmost extent of the breeding range, face an extended, shallow, temperate, and productive continental shelf. We integrated tracking data from 98 animals (juveniles and adults, males and females) gathered over more than two decades, and found that although all available habitats were used, individuals segregated by age and sex. Juvenile males favored shelf habitats, whereas subadult and adult males also used the shelf break. Juvenile females preferred the shelf and the more distant Argentine Basin used by postbreeding and postmolt adult females. Males showed the highest proportion of area‐restricted search locations, suggesting more spatially concentrated feeding activity, and likely reflecting a preference for foraging habitat and prey. Our results are consistent with those from other populations, implying that elephant seals show remarkable similarities in habitat use by age and sex classes, despite broad differences in the offshore habitats between sub‐Antarctic and temperate ecosystems.

Sea otters are marine specialists but diet generalists, which feed primarily on benthic mega-invertebrates (i.e., body dimension >1 cm). They locate and capture epibenthic and infaunal prey with their forepaws by relying on vision and tactile sensitivity during short-duration dives (generally

Female sea otters become sexually mature at 2–4 years of age. Birth may occur throughout the year with a normal litter size of one. The reproductive cycle (period of gestation and dependency) is ~12 months, so female sea otters are normally either pregnant or caring for a pup. After birth, the female provides the pup with high-fat milk from two mammary glands on the lower abdomen. Female sea otters are income breeders and must feed daily to maintain milk production, although small fat reserves, which develop during gestation, may reduce the need to forage during the initial 3 weeks post partum. Maternal behavior, which is influenced by hormones and sensory cues, manifests as vigilance against abiotic or biotic threats to neonates, allogrooming (pup grooming provided by the female), and nursing. Sea otters often give birth on the surface of the water, so there is an immediate threat to the pup from drowning, hypothermia, and predation. Pups are altricial and dependent on the female for care (nursing and grooming) and protection, although maternal behavior changes in synchrony with the pup’s physical and behavioral development. Neonates sleep and nurse most of the day, but new behaviors, such as transiting (i.e., surface swimming), self-grooming, foraging, and interacting, develop over the first 3 months of life. In response, the female exhibits reduced vigilance and enhanced foraging to support the growing pup’s nutritional needs with both milk and prey. At some point, this energetic demand may exceed the female’s foraging ability and cause a decrease in body condition, which could lead to pup abandonment or early weaning in severe cases. This behavior enables the female to survive and raise future offspring and enhance fitness. As a result, pup survival will vary geographically and annually in synchrony with favorable conditions. After females wean or abandon their pups, mating occurs within a few days to weeks, and the cycle repeats.

The reproductive system of sea otters is resource defense polygyny in which males defend territories containing resources that attract females. As a result, the predominant trait of social-sexual behavior is segregation by age and sex. Males attempt to mate with females that enter their territories, but they cannot control their movements. An estrous female that is sexually receptive to the male may form a consortship, which typically lasts ~3 days and involves multiple copulations. Copulatory behavior induces reflex ovulation in females. Key components of male sea otter reproductive behavior include sexual segregation, resource defense polygyny, aquatic mating, and no participation in rearing offspring. The reproductive system of sea otters is more similar to some species of Phocidae (true seals) than to other species of otters, likely because mating occurs at sea.

Morphology and physiology enable but also constrain an animal’s behavior and physical performance, and sensory systems affect how an animal perceives its environment. Sea otters are grouped with other raptorial predators even though they capture and manipulate prey with their forepaws and consume it at the water’s surface. They have a short, robust skull and mandibles that enhance bite force. Their postcanine teeth have rounded or conical cusps and large surfaces for cracking or crushing mollusk shells, crustacean exoskeletons, or the test of echinoderms, such as sea urchins. The axial skeleton of sea otters is modified for aquatic locomotion, with a flexible spine and foreshortened limbs to reduce hydrodynamic drag. Forelimbs are used to capture and manipulate prey and for using tools (e.g., rocks) to open hard-shelled prey, but not for locomotion. Sea otters use dorsoventral undulation with simultaneous pelvic paddling during routine submerged swimming, and their hindfeet are modified into flippers for more efficient thrust. Because of their large lung volume, sea otters are positively buoyant and rest (sleep) effortlessly or swim in supine position at the surface, using alternate stroking of the hind flippers, although they are clumsy and slow when walking on land. To offset the high thermal conductivity of water, sea otters have a mass-specific basal metabolic rate that is 2.9-fold higher than a terrestrial eutherian mammal. As a result, they consume about 25% of their body mass daily, which requires them to spend 14–50% of their activity budget foraging. Because sea otters rely almost exclusively on fur for thermal insulation, they groom (felt) their dense fur to trap an air layer next to the skin, and this essential behavior represents a significant part of the daily activity budget. Sea otters have dichromatic color vision, underwater acuity similar to other marine mammals, and the aerial acuity of many terrestrial mammals. Although sea otters detect underwater sounds, hearing is primarily adapted for air, and they do not vocalize underwater. Their forepaws have good tactile surface discrimination for identifying prey by touch, but the role of their vibrissae in foraging is uncertain. Sea otters discriminate odorants and have a vomeronasal gland, which may detect pheromones that convey social or sexual (endocrine) cues that influence behavior and reproductive physiology. Based on the presence of taste buds, sea otters may have a gustatory sense. Compared to cetaceans, the sensory systems of sea otters are more similar to amphibious pinnipeds and terrestrial carnivorans.

Northern elephant seals (NES, Mirounga angustirostris) undergo an annual molt during which they spend ∼40 days fasting on land with reduced activity and lose approximately one-quarter of their body mass. Reduced activity and muscle load in stereotypic terrestrial mammalian models results in decreased muscle mass and capacity for force production and aerobic metabolism. However, the majority of lost mass in fasting female NES is from fat while muscle mass is largely preserved. Although muscle mass is preserved, potential changes to the metabolic and contractile capacity are unknown. To assess potential changes in NES skeletal muscle during molt, we collected muscle biopsies from 6 adult female NES before the molt and after ∼30 days at the end of the molt. Skeletal muscle was assessed for respiratory capacity using high resolution respirometry, and RNA was extracted to assess changes in gene expression. Despite a month of reduced activity, fasting, and weight loss, skeletal muscle respiratory capacity was preserved with no change in OXPHOS respiratory capacity. Molt was associated with 162 upregulated genes including those favoring lipid metabolism. We identified 172 downregulated genes including those coding for ribosomal proteins and genes associated with skeletal muscle force transduction and glucose metabolism. Following ∼30 days of molt, NES skeletal muscle metabolic capacity is preserved although mechanotransduction may be compromised. In the absence of exercise stimulus, fasting-induced shifts in muscle metabolism may stimulate pathways associated with preserving the mass and metabolic capacity of slow oxidative muscle.

Most activities of Weddell seals (Leptonychotes weddellii) occur during under-ice dives that extend hundreds to thousands of meters and require the seals to hold their breath for 15 min or more. In the fast-ice environment of Antarctica, holes in the ice where seals can surface to breathe are scarce. Consequently, seals must return to a previous breathing hole or locate a new one to avoid drowning; how they navigate underwater with such precision is not known. This study individually displaced ten seals, each fitted with an archival data logger, to unfamiliar locations and analyzed the three dimensional paths of voluntary dives to test eight predictions under four hypothesized way-finding tactics: geomagnetic sensitivity, path integration, pilotage, and hydrodynamic trail following. Analyses of dive tracks provided strong evidence that Weddell seals primarily used pilotage via visible, overhead features to return home during individual dives under ice cover. Upon release at an unfamiliar location, long-distance diving began only after a period of short-distance diving. Outbound paths of dives progressively increased in distance from home. Homeward paths were remarkably straight and oriented directly toward home, or they traveled to a frequented route then turned toward home. Seventy-five percent of the frequented routes were directly below known linear disturbances in the snow on the top of the sea ice. There was little evidence that seals used geomagnetic or hydrodynamic cues, nor that homing ability was hindered by low light levels (twilight). These results contribute to a growing body of literature indicating that animals can learn to use artificial, and sometimes ephemeral landmarks to guide their movements. How Weddell seals are able to dive during polar winter, with only starlight and moonlight to illuminate landmarks, remains unknown.

Fil: Castro, Eduardo Fidel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tandil. Centro de Investigacion Veterinaria de Tandil. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigacion Veterinaria de Tandil. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Centro de Investigacion Veterinaria de Tandil; Argentina

Identifying factors that influence animal population density can provide insight into why it varies spatially and temporally and when a recovering population has reached an equilibrium density because of food resources (i.e., carrying capacity K). Although food availability is widely recognized as an important extrinsic factor limiting sea otter (Enhydra lutris) population density, can we determine when a population has reached K based on population size and prey availability ? The goal of this study was to estimate K for Simpson Bay, Alaska by measuring the abundance of edible bivalves, the primary prey for sea otters for over 40 years. We then compared prey abundance and estimated replacement rate (i.e., the mean age of bivalves predated by sea otters) to estimated annual prey consumption based on the mean population density for the past 18 years. On average, 110 adult sea otters (5.2 km−2) have occupied Simpson Bay annually since 2001 consuming an estimated 176,660 kg of bivalves. The total biomass (standing stock) of the major bivalves (predominately butter clams and stained macomas) was 785,730 kg, so adult sea otters consumed about 22% annually. Given the stable abundance of sea otters over the past 18 years and evidence of sustainable prey replacement, sea otters in Simpson Bay appear to be at K . Understanding which factors regulate population density may be one of the most challenging ecological questions and require long-term monitoring for complete resolution. We suggest that studies such as this, when applied to a variety of littoral habitats occupied by sea otters, complement approaches that use proxies for prey availability to assess K. Future research should focus on a few sites, which are representative of the variety of littoral habitats occupied by sea otters around the North Pacific Rim. From those sites, we may learn how the balance among intrinsic and extrinsic factors affects regional sea otter population density. In addition, this approach provides a mechanistic assessment of K, which will better inform probabilistic inferences for sea otter population trends and help resource managers anticipate potential conflicts and tailor management strategies to benefit a wide range of recovering predators, such as the sea otter.

The goal of this study was to classify dives of free-ranging female southern elephant seals Mirounga leonina from Península Valdés, Argentina, during their 2 mo post-breeding migration. Classifications were based on 3-dimensional movements and video-recorded observationsfrom 13 797 dives obtained by attaching video and data recorders to the backs of 8 seals. We inferred behavioral functions for the dive classes based on video-recorded observations. Three dive types were identified: foraging, resting, and transit. Most (98%) prey captures occurred during foraging dives, and primary prey were pencil smelt and myctophids. Over deep water, foraging dives were deep (maximum depth 553 ± 258 m, mean ± SD), long in duration (21.5 ± 5.8 min), and meandering with bursts of speed, steep descent and ascent angles, and vertical head movements associated with prey capture. Resting dives were shallower (maximum depth 375 ± 114 m) but lasted longer (22.6 ± 6.2 min), with lower stroking rates and speeds and greater variation inpitch and roll angle during descent. Transit dives were shallower (maximum depth 307 ± 171 m),shorter (19.9 ± 6.6 min), and more linear, with higher swim speeds and stroking rates, shallowerascent angles, and farther straight-line distances traveled. Seals exhibited several strategies toreduce the energetic cost of foraging, including gliding during descent, swimming at optimal speeds for energy savings during foraging dive ascents, ascending at the most cost-effectiveangles during transit dives, and resting preferentially during daytime hours when prey are deepestand foraging dives are less efficient. Fil: McGovern, K.A.. Texas A&M University; Estados Unidos Fil: Rodriguez, Diego Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Lewis, Mirtha Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Davis, R.W. Texas A&M University; Estados Unidos

The foraging strategies of gestating female elephant seals (Mirounga leonina) from Península Valdés, Patagonia, were assessed by analyzing the values of stable isotopes of carbon (C) and nitrogen (N) from whiskers of 60 weanlings as a proxy for maternal spatial niche utilization. The data were combined with isotopic values and at-sea satellite locations of juvenile seals and adult female satellite tracks to provide classifications of the likely foraging strategies of the mothers of the studied pups. Based on at-sea locations during the austral summer, females foraged in oceanic waters while juveniles foraged both in neritic and in oceanic habitats. Weanling isotopic values (n = 60 pups) ranged from -19.9 to -14.8? for C and from 10.6 to 18.9? for N. The degree of variation of spatial niche distribution exhibited individual patterns of habitat use over time and revealed significant intra-population differences. Ten percent of the individuals exhibited neritic maternal for-aging (δ 13 C = -15.6 ± 0.5?, δ 15 N = 17.3 ± 1.1?) and high consistency, thus suggesting specialization (%CV δ 13 C values = 0.3 to 2.2), while 90% of the individuals exhibited oceanic maternal for-aging (δ 13 C = -17.9 ± 0.7?, δ 15 N = 12.4 ± 0.5). Additionally, oceanic maternal foraging could be further classified to distinguish broader individual variability: 58% were specialists (%CV = 0.03 to 2.2), 30% were intermediate specialists-general-ists (%CV = 2.5 to 4.5), and 12% were general-ists (%CV = 5.0 to 7.3). The prevailing strategy for females was oceanic foraging as exhibited by location at sea and the greater extent of oceanic habitats (88%) potentially available for forag-ing. At the population level, the existence of both alternate foraging strategies and high individual variability exhibited by gestating females in a high-quality foraging area such as the oceanic environment of the Argentine Basin may confer an ecological edge to these females to succeed in a less predictable (although fairly rich) environment, thus influencing population trends. Fil: Eder, Elena Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina Fil: Muelbert, Mônica M.C.. Universidade Federal Do Rio Grande.; Brasil. University of Tasmania; Australia Fil: Hindell, Mark A.. University of Tasmania; Australia Fil: Davis, Randall W.. Texas A&M University; Estados Unidos Fil: Rodríguez, Diego Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Lewis, Mirtha Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina

Recent studies have suggested myoglobin (Mb) may have other cellular functions in addition to storing and transporting O2. Indeed, NMR experiments have shown that the saturated fatty acid (FA) palmitate (PA) can interact with myoglobin (Mb) in its ligated state (MbCO and MbCN) but does not interact with Mb in its deoxygenated state. The observation has led to the hypothesis that Mb can also serve as a fatty acid transporter. The present study further investigates fatty acid interaction with the physiological states of Mb using the more soluble but unsaturated fatty acid, oleic acid (OA). OA binds to MbCO but does not bind to deoxy Mb. OA binding to Mb, however, does not alter its O2 affinity. Without any Mb, muscle has a significantly lower level of triglyceride (TG). In Mb knock-out (MbKO) mice, both heart and skeletal muscles have lower level of TG relative to the control mice. Training further decreases the relative TG in the MbKO skeletal muscle. Nevertheless, the absence of Mb and lower TG level in muscle does not impair the MbKO mouse performance as evidenced by voluntary wheel running measurements. The results support the hypothesis of a complex physiological role for Mb, especially with respect to fatty acid metabolism.

Lactation is a critical and energetically expensive period of reproduction, especially for female sea otters (Enhydra lutris) and their pups, both of which have resting metabolic rates that are ca. 2.5-fold higher than terrestrial mammals of similar size. The simultaneous energy budgets for female Alaskan sea otters and their pups during the first three months postpartum were calculated based on published activity budgets for wild animals and metabolic rates for specific behaviors of captive sea otters. Pups were classified into three behavioral/size categories: Category 1 (C1) 0–

The conservation and management of sea otters has benefited from a dedicated research effort over the past 60 years enabling this species to recover from a few thousand in the early 20th century to about 150,000 today. Continued research to allow full, pre-exploitation recovery and restoration of nearshore ecosystems should focus on at least seven key challenges: (1) Defining sea otter populations at smaller spatial scales that reflect this species’ life history and dispersal patterns; (2) Understanding factors that regulate sea otter population density with a focus on index sites that are representative of the variety of littoral habitats occupied by sea otters around the North Pacific Rim; (3) Quantifying the effects of sea otters on the littoral community with a focus on how food availability limits population and ecosystem recovery and on predicting the effect of sea otter reoccupation on commercially valuable invertebrates; (4) Making sea otter monitoring programs comparable across geo-political boundaries through international collaboration to optimize survey efforts both spatially and temporally and to determine the cause of changes in sea otter demographics; (5) Evaluating the conservation benefits of sea otter reintroductions into historical habitat; (6) Assessing the socioeconomic costs and benefits of sea otter range expansion to anticipate and mitigate conflicts; (7) Recognizing in conservation and management plans that sea otters can be significantly affected by higher level predators in some circumstances. Many of these challenges will require new tools including the next generation geolocation tag technology that will allow assessments of long-range movements, dispersal and gene flow in various populations.

Marine mammals are adapted to long interruptions in breathing that enable them to maintain an oxygen-based metabolism and physiological homeostasis while underwater. The pulmonary and cardiovascular changes associated with the dive response include cessation of breathing (apnea), a decrease in heart rate (bradycardia), a concurrent reduction in cardiac output, and peripheral vasoconstriction that maintains central arterial blood pressure. A dive response during aerobic dives enables marine mammals to balance the conflicting demands of (1) optimizing the distribution and use of blood and muscle oxygen stores to maximize the ADL over the normal range of diving metabolic rates and (2) ensuring that active muscle receives adequate oxygen as exertion increases. Blood volume and concentrations of blood hemoglobin and muscle myoglobin are elevated and serve as a significant oxygen store that increases aerobic dive duration. Hepatic and renal function along with digestion and assimilation continue during aerobic dives to maintain physiological homeostasis. Carnivorous marine mammals rely primarily on fat for ATP synthesis under resting, normoxic conditions, and during dives within their ADL. Herbivorous Sirenia have more carbohydrate in their diet than carnivorous marine mammals but probably rely on the aerobic metabolism of a mixture of carbohydrate, amino acids, and short-chain fatty acids, the latter of which result from the fermentation of structural polysaccharides such as cellulose.

Early Cetacea are classified as Archaeoceti (six families), and their fossils reveal the morphological and functional evolution of early, terrestrial Artiodactyla to fully aquatic Cetacea over 15 million years during the Eocene (~52 Mya). The evolution of modern Cetacea (Neoceti: Mysticeti and Odontoceti) began in the late Eocene (~37 Mya). As with Mysticeti, late Eocene Dorudontidae were a likely sister group of early Odontoceti. The evolution of Sirenia began in the early Eocene (56–48 Mya). Fossil pinnipedimorphs only extend to the late Oligocene (27–25 Mya). Morphological and molecular evidence support a monophyletic origin for the three extant families of pinnipeds (Otariidae, Odobenidae, and Phocidae) within the taxonomic order Carnivora. The earliest fossils of Enhydra sp. are from early Pleistocene (2.6–1.8 Mya). There is no fossil record to document the evolution of the physiological adaptations that occur in living marine mammals. The dive response and enhanced oxygen stores, which increased the aerobic dive duration, and blubber for thermal insulation may have been early adaptations in each of the marine mammal lineages. The exception are fur seals and the sea otter, which rely on waterproof fur. Adaptations to avoid the detrimental effects of pressure during deep diving may have come later.

Respiration refers to gas exchange between an animal and the environment. Except for sea otters, which have unusually large lungs, the lung volumes of marine and terrestrial mammals scale isometrically with body mass. Compared with terrestrial mammals, marine mammals have a larger tidal volume (relative to total lung volume), exhibit high tidal flows (especially in small Odontoceti), and breathe apneustically in which there are periods of apnea. When averaged over periods of eupnea and apnea, marine mammals have a resting respiratory rate that is much less than predicted for but an average tidal volume that is threefold larger than predicted. Barotrauma is physical damage to tissues caused by a difference in pressure between gas in the respiratory system and the surrounding fluid or tissue, and this can be avoided if the pressure equalizes. Marine mammals have a very compliant thorax that enables their lungs (primarily the alveoli) to collapse under pressure. To prevent a high partial pressures of nitrogen in blood and tissues resulting in decompression sickness and nitrogen narcosis, reinforcement of the terminal airways in the lungs of pinnipeds and Cetacea allows the alveoli to collapse eventually isolating residual gas in the non-gas-exchanging airways. There is no clear effect of pressure on enzyme and membrane structure and function in marine mammals, but how they tolerate high pressures remains unknown.

We characterized the foraging behavior and habitat associations of lactating female northern fur seals (Callorhinus ursinus) from two of four rookeries comprising the stable population on the Commander Islands (CI). The CI females included in the study were from Severo-Zapadnoe rookery (SZR in 2008 and 2009) and Servernoe rookery (SR in 2009) which are 16 km apart on the northern tip of Bering Island (BI). We used satellite-linked tags and time–depth recorders to track the animals at sea and record dive behavior. For SZR females, the average foraging trip duration, mean dive depth, and maximum travel distance for both years were 3.4 ± 1.42 days, 16 ± 9.8 m, and 85 ± 59.6 km, respectively. The same measures for SR females were 4.4 ± 1.90 days, 20 ± 9.7 m, and 159 ± 70.8 km, respectively. The mean duration of foraging trips, mean number of bouts per trip and trip duration, mean direction of foraging trips, and size of foraging areas were significantly different between females from SR and SZR. Foraging trips of females from neither rookery were associated with high chl-a concentration. Overall, females on the CI appeared to expend less time and energy during foraging trips than females on the Pribilof Islands, and this may explain why the latter population is declining while the CI population is stable.

Prince William Sound supports many commercially and culturally important species. The phytoplankton community dynamics which support and sustain the high biomass and diversity of this ecosystem are largely unknown. The aim of this study was to describe the phytoplankton community composition during the summer, the time at which this system supports many additional migrants and commercially important fisheries. Phytoplankton community composition (pigments), dissolved nutrients, Secchi depth, total and particulate organic carbon and nitrogen, and export to deep water were measured during the summers of 2008–2010. In addition, natural abundance stable isotopes (δ13C and δ15N) of particulate organic matter (POM) and faunal samples were measured in 2010. The analysis of the phytoplankton community composition using multivariate statistics showed that changes over the summer were driven by changes in the proportion of the dominant groups: diatoms, dinoflagellates, cyanobacteria, cryptophytes, chlorophytes, and prasinophytes. These changes were driven by changes in nutrients including an organic nitrogen source, phosphate, and silica and correspond to shifts in particulate concentrations. A consistent pattern was observed each year: a large Noctiluca sp. bloom in June concurrent with low nutrients, low diversity, and high particulate organic carbon (POC) concentrations was followed by a shift in the phytoplankton community to a more diverse smaller size class community in July and equilibrating in August. This annual summer bloom could be an important contributor to the energy and nutrient inputs at the base of the regional marine food web.

Sea otters represent an interesting model for studies of mammalian feeding evolution. Although they are marine mammals, sea otters returned to the sea relatively recently and feed at the surface. Therefore, they represent a transitional stage of aquatic adaptation. Currently no feeding performance studies of sea otters have been conducted. The main objective of this study was to characterize the feeding kinematic profile in sea otters. It was hypothesized that sea otters would exhibit a terrestrial feeding behavior and that they forcefully crush hard prey at large gapes. As a result, biting kinematics would be congruent with biting behavior reported for their terrestrial ancestors, thus providing additional evidence that raptorial biting is a conserved behavior even in recently aquatic mammals. Sea otters consistently used a durophagous raptorial biting mode characterized by large gapes, large gape angles and lack of lateral gape occlusion. The shorter skulls and mandibles of sea otters, along with increased mechanical advantages of the masseter and increased bite force, form a repertoire of functional traits for durophagy. Here we consider durophagy to be a specialized raptorial biting feeding mode. A comparison of feeding kinematics of wild versus captive sea otters showed no significant differences in lateral kinematic profiles, and only minor differences in three frontal kinematic profiles, which included a slower maximum opening gape velocity, a slower maximum gape opening velocity, and a slower maximum closing gape velocity in captive sea otters. Data indicate functional innovations for producing large bite forces at wide gape and gape angles.

The behavior of sea otters ( Enhydra lutris kenyoni ) with dependent pups was observed between May and August of 2005–2010 in Simpson Bay, Alaska using focal follows and instantaneous sampling. Six behaviors (foraging, grooming, resting, swimming, swimming slowly and interacting) were recorded during four, 6-h time periods (dawn [05:00–11:00], day [11:00–17:00], dusk [17:00–23:00] and night [23:00–05:00]) to create a 24-h activity budget. Overall, 1190 focal follows were conducted for a total of 595 h. Females with dependent pups spent the greatest percentage of the day resting (42%), about equal percentages foraging (18%), grooming (15%), swimming (15%), swimming slowly (8%) and interacting (2%). Field Metabolic Rate (FMR) was estimated by using the oxygen consumption (ml O 2 min − 1 kg − 1 ) for each behavior for captive otters (Yeates et al., 2007). The estimated FMR for females with a dependent pup was 12.69 MJ day − 1 with the following absolute and percentage allocations for each behavior: foraging 2.38 (19%), grooming 2.70 (21%), resting 3.42 (27%), swimming 2.64 (21%), swimming slowly 1.25 (10%) and interacting 0.3 (2%). The estimated weight specific FMR was 601 kJ day − 1 kg − 1 , similar to that reported for territorial males in the same area. The sea otter population in Simpson Bay has been stable for at least the last 12 years. It would follow then that the time spent foraging might be similar to other areas where the population is stable, but this is not the case. In Simpson Bay, the time spent foraging is more similar to areas that have been recently occupied. The relatively small amount of time spent foraging may indicate that geographic differences (structure of the near-shore community: substrate, water depth, kelp canopy, prey assemblage, and competitors) may play a greater role in determining the amount of time spent foraging than population status.

Little is known about the tactics northern elephant seals (NES) use to capture prey due to the difficulties in observing these animals underwater. NES forage on vertically migrating prey at depths >500 m during day and at night where light levels are negligible. Although NES have increased visual sensitivity in deep water, vision is likely a limited sensory modality. Still images of NES foraging show that the mystacial vibrissae are protracted before prey capture. As a representative phocid, harbor seals can follow hydrodynamic trails using their vibrissae, and are highly sensitive to water velocity changes. In lieu of performance data, vibrissal innervation can be used as a proxy for sensitivity. Although comparative data are few, seals average 1,000 to 1,600 axons per vibrissa (five to eight times more than terrestrial mammals). To test the hypothesis that NES have increased innervation as other pinnipeds, vibrissae from the ventral-caudal mystacial field from nine individuals were sectioned and stained for microstructure (trichrome) and innervation (Bodian silver stain). Follicles were tripartite and consisted of lower and upper cavernous sinuses separated by a ring sinus containing an asymmetrical ringwulst. The deep vibrissal nerve penetrated the follicular capsule at the base, branched into several bundles, and coursed through the lower cavernous sinus to the ring sinus. Axons in the ring sinus terminated in the ringwulst and along the inner conical body. NES averaged 1,584 axons per vibrissa. The results add to the growing body of evidence that phocids, and perhaps all pinnipeds, possess highly sensitive mystacial vibrissae that detect prey.

Weddell seals are polar predators that must partition their time between many behaviours, including hunting prey at depth and breathing at the surface. Although they have been well studied, little is known about how foraging behaviour changes when access to breathing holes is restricted, such as in the isolated-hole paradigm. The current study took advantage of previously gathered data for seals diving at an isolated hole to compare with foraging behaviour of free-ranging seals that had access to multiple holes. We examined dive structure, hunting tactics, and allocation of time, locomotor activity and energy based on three-dimensional dive profiles and video imagery of prey encounters for two free-ranging and six isolated-hole seals. Midsummer foraging dives of free-ranging seals were remarkably similar to those of seals diving at an isolated hole, but there were differences in two behavioural states and the frequency of several behavioural transitions. Results indicate that seals employ an energetically more conservative foraging strategy when access to breathing holes is limited and prey are less abundant. These results highlight the importance of understanding the complex interactions between breathing hole access, prey abundance and other factors that may result in different Weddell seal foraging strategies under changing future conditions.

The ontogeny of diving and foraging behavior of northern fur seal pups from a stable population on Bering Island, Russia, was recorded with animal-borne instruments during their first few months at sea, a critical period during their first year at sea. Thirty-five pups were instrumented with satellite-linked time-depth recorders and stomach temperature pills. Diving occurred predominantly at night with deeper and longer dives as the pups matured. Mean dive depths were correlated with lunar illumination, whereas mean dive durations were also correlated with time of day and sex. Foraging success did not differ between sexes, and there was no relationship between meal size (as indicated by feeding event duration and minimum stomach temperature) and lunar illumination fraction or maximum foraging depth. Although most pups were able to successfully forage within 3 days of starting their migration, the number of feeding events recorded each day remained low (mean 1.6 events day−1). There was no indication of an appreciable increase in meal size after the first 2 weeks of the migration despite an increase in dive frequency and depth. The results are consistent with observations that pups do not gain mass during their first year and emphasize the risk of starvation from infrequent foraging in cold water.

The stocks of Southern sea lions (Otaria flavescens, SSL) and South American fur seals (SAFS) that breed on coastal islands of Uruguay constitute the most important focal concentration of pinnipeds in South America, with a significant increase in SAFS and a steady decrease of SSL over the past decades. Because females are a key element of population dynamics and no information exists on the post-breeding pup rearing period, we studied the foraging patterns of SSL females in the La Plata River Estuary (LPRE) during mid and late lactation (late austral autumn and winter), analyzing the foraging performance, geographic coverage and ontogenetic differences in foraging strategies for a period of 1-5 months. At-sea movements of 22 SSL females (6 subadults and 16 adults) from Isla de Lobos (IL, 35°01'28"S-54°52'59"W, Uruguay) were monitored using satellite transmitters (SPOT4, SPOT5 and STDR-S16, Wildlife Computers) in 2007 and 2010. An algorithm [McConnell, B.J., Chambers, C., Fedak, M.A., 1992. Foraging ecology of southern elephant seals in relation to the bathymetry and productivity of the Southern Ocean. Antarct. Sci. 4, 393-398.] with a maximum transit speed of 3ms-1 was applied to the Argos information, resulting in a total of 2522 filtered locations. A daily mean of 3.5±1.74 filtered locations per animal was received. One hundred and eighty three foraging trips (FT) were recorded with no significant differences (p

The goal of this study was to classify free-ranging (FR) dives of Weddell seals (Leptonychotes weddellii) and to compare them to isolated hole (IH) dives. Classification and comparisons were based on 58 descriptors for three-dimensional dive paths computed from data obtained by attaching video and data recorders to the backs of 12 adult Weddell seals that were free-ranging in eastern McMurdo Sound, Antarctica. We then inferred behavioral functions for the dive classes based on video-recorded observations. Three of the four dive types previously identified from seals diving at an IH occurred in FR seals. Although there were differences associated with location, Types 1, 2 and 3 dives clustered in a similar pattern in the discriminant analysis for FR and IH dives. Most prey (79%) captures occurred during Type 1 dives, and the primary (99%) prey was Antarctic silverfish (Pleuragramma antarcticum). Type 1 dives were the deepest (mean maximum depth 324–378 m), longest in duration (15.0–27.0 min), covered the greatest total distance (1470–2197 m), and had the steepest dive angles (descents: −30°; ascents: +27°). Types 2 and 3 dives formed a continuum from short duration (3.6–7.5 min), shallow (mean maximum depth 30–66 m) dives that were close to the ice hole (farpoint distance 75–130 m) and often involved aggressive interactions with other seals for breathing opportunities (Type 2) to progressively longer (7.9–17.2 min), deeper (mean maximum depth 81–143 m) dives that covered greater total distances (878–1194 m) and were associated with transiting between holes, exploring and occasionally foraging (Type 3). Very long distance Type 4 exploratory dives that were identified in the IH study were completely absent in FR seals.

Sea otters represent an interesting model for studies of mammalian feeding evolution. Although they are marine mammals, sea otters returned to the sea relatively recently and feed at the surface. Therefore, they represent a transitional stage of aquatic adaptation. Currently no feeding performance studies of sea otters have been conducted. The main objective of this study was to characterize the feeding kinematic profile in sea otters. It was hypothesized that sea otters would exhibit a terrestrial feeding behavior and that they forcefully crush hard prey at large gapes. As a result, biting kinematics would be congruent with biting behavior reported for their terrestrial ancestors, thus providing additional evidence that raptorial biting is a conserved behavior even in recently aquatic mammals. Sea otters consistently used a durophagous raptorial biting mode characterized by large gapes, large gape angles, and lack of lateral gape occlusion. The shorter skulls and mandibles of sea otters, along with increased mechanical advantages of the masseter and increased bite force, form a repertoire of functional traits for durophagy. Here we consider durophagy to be a specialized raptorial biting feeding mode. A comparison of feeding kinematics of wild vs captive sea otters showed no significant differences in lateral kinematic profiles and only minor differences in three frontal kinematic profiles, which included a slower maximum opening gape velocity, a slower maximum gape opening velocity, and a slower maximum closing gape velocity in captive sea otters. Data indicate functional innovations for producing large bite forces at wide gape and gape angles.