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Comparative physiology has developed a rich understanding of the physiological adaptations of organisms, from microbes to megafauna. Despite extreme differences in size and a diversity of habitats, general patterns are observed in their physiological adaptations. Yet, many organisms deviate from the general patterns, providing an opportunity to understand the importance of ecology in determining the evolution of unusual adaptations. Aquatic air-breathing vertebrates provide unique study systems in which the interplay between ecology, physiology and behavior is most evident. They must perform breath-hold dives to obtain food underwater, which imposes a physiological constraint on their foraging time as they must resurface to breathe. This separation of two critical resources has led researchers to investigate these organisms' physiological adaptations and trade-offs. Addressing such questions on large marine animals is best done in the field, given the difficulty of replicating the environment of these animals in the lab. This Review examines the long history of research on diving physiology and behavior. We show how innovative technology and the careful selection of research animals have provided a holistic understanding of diving mammals' physiology, behavior and ecology. We explore the role of the aerobic diving limit, body size, oxygen stores, prey distribution and metabolism. We then identify gaps in our knowledge and suggest areas for future research, pointing out how this research will help conserve these unique animals., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Among pinnipeds, southern elephant seals (SESs, Mirounga leonina) are extreme divers that dive deeply and continuously along foraging trips to restore their body stores after fasting on land during breeding or moulting. Their replenishment of body stores influences their energy expenditure during dives and their oxygen (O2) reserves (via muscular mass), yet how they manage their O2 stores during their dives is not fully understood. In this study, 63 female SESs from Kerguelen Island were equipped with accelerometers and time-depth recorders to investigate changes in diving parameters through their foraging trips. Two categories of dive behaviour were identified and related to the body size of individuals, with smaller SESs performing shallower and shorter dives requiring greater mean stroke amplitude compared with larger individuals. In relation to body size, the larger seals had lower estimated oxygen consumption levels for a given buoyancy (i.e. body density) compared with smaller individuals. However, both groups were estimated to have the same oxygen consumption of 0.079±0.001 ml O2 stroke-1 kg-1 for a given dive duration and at neutral buoyancy when the cost of transport was minimal. Based on these relationships, we built two models that estimate changes in oxygen consumption according to dive duration and body density. The study highlights that replenishing body stores improves SES foraging efficiency, as indicated by increased time spent at the bottom of the ocean. Thus, prey-capture attempts increase as SES buoyancy approaches the neutral buoyancy point., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Allometry predicts that the 12-17-g American water shrew ( Sorex palustris )-the world's smallest mammalian diver-will have the highest diving metabolic rate coupled with the lowest total body oxygen storage capacity, skeletal muscle buffering capacity, and glycolytic potential of any endothermic diver. Consistent with expectations, and potentially owing to their low thermal inertia, water shrews had a significantly higher diving metabolic rate in 10°C water (8.77 mL O 2 g -1 h -1 ) compared with 30°C water (6.57 mL O 2 g -1 h -1 ). Unlike larger-bodied divers, muscle myoglobin contributed minimally (7.7%-12.4%) to total onboard O 2 stores of juvenile and adult water shrews, respectively, but was offset by high blood O 2 carrying capacities (26.4%-26.9% v/v). Diving was predominantly aerobic, as only 1.2%-2.3% of dives in 10°C and 30°C water, respectively, exceeded the calculated aerobic dive limits at these temperatures (10.8-14.4 s). The mean voluntary dive time of water shrews during 20-min trials in 3°C-30°C water was 5.0 ± 0.1 s ( N = 25 , n = 1,628 ), with a mean maximum dive time of 10.1 ± 0.4 s. However, the average dive duration ( 6.9 ± 0.2 s, n = 257 ) of radio-telemetered shrews exclusively foraging in a simulated riparian environment (3°C water) for 12-28 h suggests that mean (but not maximum) dive times of water shrews in the wild may be longer. Mean dive duration, duration of the longest dive, and total time in water all decreased significantly as water temperature declined, suggesting that shrews employed behavioral thermoregulation to defend against immersion hypothermia. Additionally, free-diving shrews in the 24-h trials consistently elevated core body temperature by ∼1°C immediately before initiating aquatic foraging bouts and ended these bouts when body temperature was still at or above normal resting levels (∼37.8°C). We suggest that this observed predive hyperthermia aids to heighten the impressive somatosensory physiology, and hence foraging efficiency, of this diminutive predator while submerged.

Diving ectothermic vertebrates are an important component of many aquatic ecosystems, but the threat of climate warming is particularly salient to this group. Dive durations typically decrease as water temperatures rise; yet, we lack an understanding of whether this trend is apparent in all diving ectotherms and how this group will fare under climate warming. We compiled data from 27 studies on 20 ectothermic vertebrate species to quantify the effect of temperature on dive durations. Using meta-analytic approaches, we show that, on average, dive durations decreased by 11% with every 1°C increase in water temperature. Larger increases in temperature (e.g. +3°C versus +8-9°C) exerted stronger effects on dive durations. Although species that respire bimodally are projected to be more resilient to the effects of temperature on dive durations than purely aerial breathers, we found no significant difference between these groups. Body mass had a weak impact on mean dive durations, with smaller divers being impacted by temperature more strongly. Few studies have examined thermal phenotypic plasticity ( N =4) in diving ectotherms, and all report limited plasticity. Average water temperatures in marine and freshwater habitats are projected to increase between 1.5 and 4°C in the next century, and our data suggest that this magnitude of warming could translate to substantial decreases in dive durations, by approximately 16-44%. Together, these data shed light on an overlooked threat to diving ectothermic vertebrates and suggest that time available for underwater activities, such as predator avoidance and foraging, may be shortened under future warming., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

Survival of air-breathing, diving ectotherms is dependent on their capacity to optimise the time available for obligate underwater activities, such as predator avoidance. Submergence times are thermally sensitive, with dive durations significantly reduced by increases in water temperature, deeming these animals particularly vulnerable to the effects of climate change. The physiological mechanisms underlying this compromised performance are unclear but are hypothesised to be linked to increased oxygen demand and a reduced capacity for metabolic depression at elevated temperatures. Here, we investigated how water temperature (both acute and chronic exposures) affected the physiology of juvenile estuarine crocodiles ( Crocodylus porosus ) performing predator avoidance dives (i.e. fright-dives). Diving oxygen consumption, 'fright' bradycardia, haematocrit and haemoglobin (indicators of blood oxygen carrying capacity) were assessed at two test temperatures, reflective of different climate change scenarios (i.e. current summer water temperatures, 28°C, and 'high' climate warming, 34°C). Diving oxygen consumption rate increased threefold between 28 and 34°C ( Q 10 =7.4). The capacity to depress oxygen demand was reduced at elevated temperatures, with animals lowering oxygen demand from surface levels by 52.9±27.8% and 27.8±16.5% (means±s.e.m.) at 28°C and 34°C, respectively. Resting and post-fright-dive haematocrit and haemoglobin were thermally insensitive. Together these findings suggest decrements in fright-dive performance at elevated temperatures stem from increased oxygen demand coupled with a reduced capacity for metabolic depression., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2017. Published by The Company of Biologists Ltd.)

Our understanding of how air-breathing marine predators cope with environmental variability is limited by our inadequate knowledge of their ecological and physiological parameters. Because of their wide distribution along both coasts of the sub-continent, South American sea lions (Otaria byronia) provide a valuable opportunity to study the behavioral and physiological plasticity of a marine predator in different environments. We measured the oxygen stores and diving behavior of South American sea lions throughout most of its range, allowing us to demonstrate that diving ability and behavior vary across its range. We found no significant differences in mass-specific blood volumes of sea lions among field sites and a negative relationship between mass-specific oxygen storage and size, which suggests that exposure to different habitats and geographical locations better explains oxygen storage capacities and diving capability in South American sea lions than body size alone. The largest animals in our study (individuals from Uruguay) were the shallowest and shortest duration divers, and had the lowest mass-specific total body oxygen stores, while the deepest and longest duration divers (individuals from southern Chile) had significantly larger mass-specific oxygen stores, despite being much smaller animals. Our study suggests that the physiology of air-breathing diving predators is not fixed, but that it can be adjusted, to a certain extent, depending on the ecological setting and or habitat. These adjustments can be thought of as a 'training effect': as the animal continues to push its physiological capacity through greater hypoxic exposure, its breath-holding capacity increases., (© 2016. Published by The Company of Biologists Ltd.)

Physiological constraints dictate animals' ability to exploit habitats. For marine mammals, it is important to quantify physiological limits that influence diving and their ability to alter foraging behaviors. We characterized age-specific dive limits of walruses by measuring anaerobic (acid-buffering capacity) and aerobic (myoglobin content) capacities of the muscles that power hind (longissimus dorsi) and fore (supraspinatus) flipper propulsion. Mean buffering capacities were similar across muscles and age classes (a fetus, five neonatal calves, a 3 month old and 20 adults), ranging from 41.31 to 54.14 slykes and 42.00 to 46.93 slykes in the longissimus and supraspinatus, respectively. Mean myoglobin in the fetus and neonatal calves fell within a narrow range (longissimus: 0.92-1.68 g 100 g(-1) wet muscle mass; supraspinatus: 0.88-1.64 g 100 g(-1) wet muscle mass). By 3 months post-partum, myoglobin in the longissimus increased by 79%, but levels in the supraspinatus remained unaltered. From 3 months post-partum to adulthood, myoglobin increased by an additional 26% in the longissimus and increased by 126% in the supraspinatus; myoglobin remained greater in the longissimus compared with the supraspinatus. Walruses are unique among marine mammals because they are born with a mature muscle acid-buffering capacity and attain mature myoglobin content early in life. Despite rapid physiological development, small body size limits the diving capacity of immature walruses and extreme sexual dimorphism reduces the diving capacity of adult females compared with adult males. Thus, free-ranging immature walruses likely exhibit the shortest foraging dives while adult males are capable of the longest foraging dives., (© 2015. Published by The Company of Biologists Ltd.)

Most marine mammals are hypothesized to routinely dive within their aerobic dive limit (ADL). Mammals that regularly perform deep, long-duration dives have locomotor muscles with elevated myoglobin concentrations that are composed of predominantly large, slow-twitch (Type I) fibers with low mitochondrial volume densities (V(mt)). These features contribute to extending ADL by increasing oxygen stores and decreasing metabolic rate. Recent tagging studies, however, have challenged the view that two groups of extreme deep-diving cetaceans dive within their ADLs. Beaked whales (including Ziphius cavirostris and Mesoplodon densirostris) routinely perform the deepest and longest average dives of any air-breathing vertebrate, and short-finned pilot whales (Globicephala macrorhynchus) perform high-speed sprints at depth. We investigated the locomotor muscle morphology and estimated total body oxygen stores of several species within these two groups of cetaceans to determine whether they (1) shared muscle design features with other deep divers and (2) performed dives within their calculated ADLs. Muscle of both cetaceans displayed high myoglobin concentrations and large fibers, as predicted, but novel fiber profiles for diving mammals. Beaked whales possessed a sprinter's fiber-type profile, composed of ~80% fast-twitch (Type II) fibers with low V(mt). Approximately one-third of the muscle fibers of short-finned pilot whales were slow-twitch, oxidative, glycolytic fibers, a rare fiber type for any mammal. The muscle morphology of beaked whales likely decreases the energetic cost of diving, while that of short-finned pilot whales supports high activity events. Calculated ADLs indicate that, at low metabolic rates, both beaked and short-finned pilot whales carry sufficient onboard oxygen to aerobically support their dives.

Animals that hunt for food underwater and return to the surface for air ('divers') are limited by their ability to store oxygen. The aerobic dive limit (ADL) is the dive duration at which all the possible oxygen stores have been used. It has been claimed that models of optimal diving predict that divers will be close to this limit and that the data do not match this prediction. I characterize closeness to the ADL by the fraction ψ of the maximum amount of stored oxygen that is used during a dive. At the ADL this fraction is 1. I show that an optimal diver does not necessarily have a ψ close to 1 and point out that the key feature predicted by the model is that the diver should have no oxygen stores left when it returns to the surface. The data cited against optimal diving do not address this issue. • Animals that dive for food and return to surface for air are limited by oxygen stores. • Models claim that optimal divers should use nearly all their maximum oxygen stores. • I develop a measure of oxygen use for divers and illustrate it with data from whales. • I show that optimal diving does not predict that the maximum amount of oxygen is used. • I argue that the data cited against optimal diving do not address this issue. [ABSTRACT FROM AUTHOR]

Adult Weddell seals (Leptonychotes weddellii) haul-out on the ice in October/November (austral spring) for the breeding season and reduce foraging activities for ~4 months until their molt in the austral fall (January/February). After these periods, animals are at their leanest and resume actively foraging for the austral winter. In mammals, decreased exercise and hypoxia exposure typically lead to decreased production of O2-carrying proteins and muscle wasting, while endurance training increases aerobic potential. To test whether similar effects were present in marine mammals, this study compared the physiology of 53 post-molt female Weddell seals in the austral fall to 47 pre-breeding females during the spring in McMurdo Sound, Antarctica. Once body mass and condition (lipid) were controlled for, there were no seasonal changes in total body oxygen (TBO2) stores. Within each season, hematocrit and hemoglobin values were negatively correlated with animal size, and larger animals had lower mass-specific TBO2 stores. But because larger seals had lower mass-specific metabolic rates, their calculated aerobic dive limit was similar to smaller seals. Indicators of muscular efficiency, myosin heavy chain composition, myoglobin concentrations, and aerobic enzyme activities (citrate synthase and β-hydroxyacyl CoA dehydrogenase) were likewise maintained across the year. The preservation of aerobic capacity is likely critical to foraging capabilities, so that following the molt Weddell seals can rapidly regain body mass at the start of winter foraging. In contrast, muscle lactate dehydrogenase activity, a marker of anaerobic metabolism, exhibited seasonal plasticity in this diving top predator and was lowest after the summer period of reduced activity.

Understanding the diving behavior of semiaquatic mammals, particularly in relation to estimated aerobic dive limits and diet, is important to understand their adaptability and potential vulnerability to changes in prey type and distribution. The diving behavior of African clawless otters, Aonyx capensis , and spotted-necked otters, Hydrictis maculicollis , is poorly known, and no estimates of their dive performance in relation to targeted prey and calculated dive limits have been reported previously for freshwater environments. We investigated the diving behavior of both these otter species in freshwater environments within South Africa through video recordings of direct observations and subsequent video analyses where dive and recovery durations and dive function were recorded. African clawless otters were found to perform longer dives (mean ± SD = 26.9 ± 12.2 s), compared to spotted-necked otters (8.5 ± 7.6 s). African clawless otters showed substantial variation in dive durations, with the shortest dives sometimes lasting < 5 s, and the longest recorded dive being 70 s. The majority of spotted-necked otter dives lasted < 10 s, with the shortest recorded dive lasting 0.66 s and the longest recorded dive lasting 50.9 s. Spotted-necked otters performed different dive types that were evidently dependent on prey targeted, with dives targeting crabs (16.10 ± 1.91 s) being longer than dives targeting rainbow trout, Oncorhynchus mykiss (5.58 ± 0.17 s). The theoretical dive durations of African clawless otters were exceeded during play dives, while spotted-necked otters sometimes exceeded their theoretical dive durations when performing successful foraging dives. The results of this study suggest that spotted-necked otters can vary behavior in relation to prey and exceed theoretical dive duration during successful foraging dives to maximize the net rate of energy gain. Furthermore, when considering known individual-level dietary specialization and plasticity in these species, it may be predicted that dive behaviors are likely to vary substantially among individuals, and in relation to prey availability and localized habitat conditions. [ABSTRACT FROM AUTHOR]

Northern fur seal ( Callorhinus ursinus; NFS) populations have been declining, perhaps due to limited foraging ability of pups. Because a marine mammal's proficiency at exploiting underwater prey resources is based on the ability to store large amounts of oxygen (O) and to utilize these reserves efficiently, this study was designed to determine if NFS pups had lower blood, muscle, and total body O stores than adults. Pups (<1-month old) had a calculated aerobic dive limit only ~40% of adult females due to lower blood and, to a much greater extent, muscle O stores. Development of the Pectoralis ( Pec) and Longissimus dorsi ( LD) skeletal muscles was further examined by determining their myosin heavy chain (MHC) composition and enzyme activities. In all animals, the slow MHC I and fast-twitch IIA proteins typical of oxidative fiber types were dominant, but adult muscles contained more ( Pec ~50%; LD ~250% higher) fast-twitch MHC IID/X protein characteristic of glycolytic muscle fibers, than pup muscles. This suggests that adults have greater ability to generate muscle power rapidly and/or under anaerobic conditions. Pup muscles also had lower aerobic and anaerobic ATP production potential, as indicated by lower metabolically scaled citrate synthase, β-hydroxyacyl CoA dehydrogenase, and lactate dehydrogenase activities (all P values ≤0.001). In combination, these findings indicate that pups are biochemically and physiologically limited in their diving capabilities relative to adults. This may contribute to lower NFS first year survival. [ABSTRACT FROM AUTHOR]

The physiological basis of the aerobic dive limit (ADL), the dive duration associated with the onset of post-dive blood lactate elevation, is hypothesized to be depletion of the muscle oxygen (O2) store. A duel wavelength near-infrared spectrophotometer was developed and used to measure myoglobin (Mb) O2 saturation levels in the locomotory muscle during dives of emperor penguins (Aptenodytes forsteri). Two distinct patterns of muscle O2 depletion were observed. Type A dives had a monotonic decline, and, in dives near the ADL, the muscle O2 store was almost completely depleted. This pattern of Mb desaturation was consistent with lack of muscle blood flow and supports the hypothesis that the onset of post-dive blood lactate accumulation is secondary to muscle O2 depletion during dives. The mean type A Mb desaturation rate allowed for calculation of a mean muscle O2 consumption of 12.4 ml O2kg-1 muscle min-1, based on a Mb concentration of 6.4g 100g-1 muscle. Type B desaturation patterns demonstrated a more gradual decline, often reaching a mid-dive plateau in Mb desaturation. This mid-dive plateau suggests maintenance of some muscle perfusion during these dives. At the end of type B dives, Mb desaturation rate increased and, in dives beyond the ADL, Mb saturation often reached near 0%. Thus, although different physiological strategies may be used during emperor penguin diving, both Mb desaturation patterns support the hypothesis that the onset of post-dive lactate accumulation is secondary to muscle O2 store depletion [ABSTRACT FROM AUTHOR]

A mathematical model was used to explore if elevated levels of N2, and risk of decompression sickness (DCS), could limit dive performance (duration and depth) in king penguins (Aptenodytes patagonicus). The model allowed prediction of blood and tissue (central circulation, muscle, brain and fat) N2 tensions (PN2) based on different cardiac outputs and blood flow distributions. Estimated mixed venous PN2 agreed with values observed during forced dives in a compression chamber used to validate the assumptions of the model. During bouts of foraging dives, estimated mixed venous and tissue PN2 increased as the bout progressed. Estimated mean maximum mixed venous PN2 upon return to the surface after a dive was 4.56±0.18 atmospheres absolute (ATA; range: 4.37–4.78 ATA). This is equivalent to N2 levels causing a 50% DCS incidence in terrestrial animals of similar mass. Bout termination events were not associated with extreme mixed venous N2 levels. Fat PN2 was positively correlated with bout duration and the highest estimated fat PN2 occurred at the end of a dive bout. The model suggested that short and shallow dives occurring between dive bouts help to reduce supersaturation and thereby DCS risk. Furthermore, adipose tissue could also help reduce DCS risk during the first few dives in a bout by functioning as a sink to buffer extreme levels of N2. [ABSTRACT FROM AUTHOR]

The physiological and behavioural development of diving was examined in Australian fur seal ( Arctocephalus pusillus doriferus) pups to assess whether animals at weaning are capable of exploiting the same resources as adult females. Haematocrit, haemoglobin and myoglobin contents all increased throughout pup development though total body oxygen stores reached only 71% of adult female levels just prior to weaning. Oxygen storage components, however, did not develop at the same pace. Whereas blood oxygen stores had reached adult female levels by 9 months of age, muscle oxygen stores were slower to develop, reaching only 23% of adult levels by this age. Increases in diving behaviour corresponded to the physiological changes observed. Pups spent little time (<8%) in the water prior to moulting (age 1–2 months) whereas following the moult, they spent >27% of time in the water and made mid-water dives (maximum depth 35.7 ± 2.9 m) with durations of 0.35 ± 0.03 min. By 9 months (just prior to weaning), 30.5 ± 9.3% of all dives performed were U-shaped benthic dives (maximum depth 65.0 ± 6.0 m) with mean durations of 0.87 ± 0.25 min, significantly shorter than those of adult females. These results suggest that while Australian fur seal pups approaching the age of weaning are able to reach similar depths as adult females, they do not have the physiological capacity to remain at these depths for sufficient durations to exploit them to the same efficiency. [ABSTRACT FROM AUTHOR]

Sound-and-orientation recording tags (DTAGs) were used to study 10 beaked whales of two poorly known species, Ziphius cavirostris (Zc) and Mesoplodon densirostris (Md). Acoustic behaviour in the deep foraging dives performed by both species (Zc: 28 dives by seven individuals; Md: 16 dives by three individuals) shows that they hunt by echolocation in deep water between 222 and 1885 m, attempting to capture about 30 prey/dive. This food source is so deep that the average foraging dives were deeper (Zc: 1070 m; Md: 835 m) and longer (Zc: 58 mm; Md: 47 mm) than reported for any other air-breathing species. A series of shallower dives, containing no indications of foraging, followed most deep foraging dives. The average interval between deep foraging dives was 63 mm for Zc and 92 mm for Md. This long an interval may be required for beaked whales to recover from an oxygen debt accrued in the deep foraging dives, which last about twice the estimated aerobic dive limit. Recent reports of gas emboli in beaked whales stranded during naval sonar exercises have led to the hypothesis that their deep-diving may make them especially vulnerable to decompression. Using current models of breath-hold diving, we infer that their natural diving behaviour is inconsistent with known problems of acute nitrogen supersaturation and embolism. If the assumptions of these models are correct for beaked whales, then possible decompression problems are more likely to result from an abnormal behavioural response to sonar. [ABSTRACT FROM AUTHOR]

Abstract: The original definition of aerobic dive limit (ADL) was the dive duration after which there is an increase in post-dive concentration of lactate in the blood of Weddell seals freely diving in the field. The only other species in which such measurements have been made is the emperor penguin. For all other species, aerobic dive limit has been calculated (cADL) by dividing usable oxygen stores with an estimation of the rate of oxygen consumption during diving. Unfortunately, cADL is often referred to as the aerobic dive limit, implying that it is equivalent to that determined from the measurement of post-dive blood lactate concentration. However, this is not so, as at cADL all of the usable oxygen would have been consumed, whereas Weddell seals and emperor penguins can dive for at least 2–3 times longer than their ADL. Thus, at ADL, there is still some usable oxygen remaining in the stores. It is suggested that to avoid continued confusion between these two terms, the former is called diving lactate threshold (DLT), as it is somewhat analogous to the lactate threshold in exercising terrestrial vertebrates. Possible explanations of how some species routinely dive beyond their cADL are also discussed. [Copyright &y& Elsevier]

Abstract: Diving animals offer a unique opportunity to study the importance of physiological constraint and the limitation it can impose on animal''s behaviour in nature. This paper examines the interaction between physiology and behaviour and its impact on the diving capability of five eared seal species (Family Otariidae; three sea lions and two fur seals). An important physiological component of diving marine mammals is the aerobic dive limit (ADL). The ADL of these five seal species was estimated from measurements of their total body oxygen stores, coupled with estimates of their metabolic rate while diving. The tendency of each species to exceed its calculated ADL was compared relative to its diving behaviour. Overall, our analyses reveal that seals which forage benthically (i.e. on the sea floor) have a greater tendency to approach or exceed their ADL compared to seals that forage epipelagically (i.e. near the sea surface). Furthermore, the marked differences in foraging behaviour and physiology appear to be coupled with a species demography. For example, benthic foraging species have smaller populations and lower growth rates compared to seal species that forage epipelagically. These patterns are relevant to the conservation and management of diving vertebrates. [Copyright &y& Elsevier]

The energetic cost of diving in marine mammals is a difficult value to derive given the problems of assessing metabolic rate for an animal at sea. Nevertheless, it is fundamental to our understanding of the foraging strategies of air-breathers exploiting underwater food sources. We measured the metabolic rates of eight captive grey seals, voluntarily diving in a quasi-natural setting. Oxygen consumption during post-dive surface periods was measured using open-flow respirometry, and dive behaviour of the seals was recorded using time depth recorders (TDRs). Mean diving metabolic rate (DMR) for both adults and juveniles was 1.7 times the predicted standard metabolic rate of terrestrial animals of equal size. For all animals, DMR was lower than the rate of metabolism measured whilst they were resting at the water's surface. On a dive-by-dive basis, DMR decreased with dive duration but increased with mean swim speed. Regressing the maximum 5% of DMRs against dive duration resulted in a significant negative relationship that was not significantly different from the relationship between the calculated maximum rate of aerobic metabolism and dive duration, suggesting that these seals were diving within, and up to, their aerobic limits. We developed a model that allows the prediction of DMR from information on dive behaviour of the type routinely collected in telemetry studies of wild seals. The model accurately predicts DMR using behavioural data from periods of diving with known metabolism data. This model can be used to predict the at-sea metabolic rate of wild grey seals, an important input into ecosystem models. [ABSTRACT FROM AUTHOR]

We investigated the diving behaviour, the time allocation of the dive cycle and the behavioural aerobic dive limit (ADL) of platypuses (Ornithorhynchus anatinus) living at a sub-alpine Tasmanian lake. Individual platypuses were equipped with combined data logger–transmitter packages measuring dive depth. Mean dive duration was 31.3 s with 72% of all dives lasting between 18 and 40 s. Mean surface duration was 10.1 s. Mean dive depth was 1.28 m with a maximum of 8.77 m. Platypuses performed up to 1600 dives per foraging trip with a mean of 75 dives per hour. ADL was estimated by consideration of post-dive surface intervals vs. dive durations. Only 15% of all dives were found to exceed the estimated ADL of 40 s, indicating mainly aerobic diving in the species. Foraging platypuses followed a model of optimised recovery time, the optimal breathing theory. Total bottom duration or total foraging duration per day is proposed as a useful indicator of foraging efficiency and hence habitat quality in the species. [Copyright &y& Elsevier]