In this Review, we focus on the functional properties of the respiratory system of pinnipeds and cetaceans, and briefly summarize the underlying anatomy; in doing so, we provide an overview of what is currently known about their respiratory physiology and mechanics. While exposure to high pressure is a common challenge among breath-hold divers, there is a large variation in respiratory anatomy, function and capacity between species -how are these traits adapted to allow the animals to withstand the physiological challenges faced during dives? The ultra-deep diving feats of some marine mammals defy our current understanding of respiratory physiology and lung mechanics. These animals cope daily with lung compression, alveolar collapse, transient hyperoxia and extreme hypoxia. By improving our understanding of respiratory physiology under these conditions, we will be better able to define the physiological constraints imposed on these animals, and how these limitations may affect the survival of marine mammals in a changing environment. Many of the respiratory traits to survive exposure to an extreme environment may inspire novel treatments for a variety of respiratory problems in humans.

Hydrostatic lung compression in diving marine mammals, with collapsing alveoli blocking gas exchange at depth, has been the main theoretical basis for limiting N2 uptake and avoiding gas emboli (GE) as they ascend. However, studies of beached and bycaught cetaceans and sea turtles imply that air-breathing marine vertebrates may, under unusual circumstances, develop GE that result in decompression sickness (DCS) symptoms. Theoretical modelling of tissue and blood gas dynamics of breath-hold divers suggests that changes in perfusion and blood flow distribution may also play a significant role. The results from the modelling work suggest that our current understanding of diving physiology in many species is poor, as the models predict blood and tissue N2 levels that would result in severe DCS symptoms (chokes, paralysis and death) in a large fraction of natural dive profiles. In this review, we combine published results from marine mammals and turtles to propose alternative mechanisms for how marine vertebrates control gas exchange in the lung, through management of the pulmonary distribution of alveolar ventilation () and cardiac output/lung perfusion (), varying the level of in different regions of the lung. Man-made disturbances, causing stress, could alter the mismatch level in the lung, resulting in an abnormally elevated uptake of N2, increasing the risk for GE. Our hypothesis provides avenues for new areas of research, offers an explanation for how sonar exposure may alter physiology causing GE and provides a new mechanism for how air-breathing marine vertebrates usually avoid the diving-related problems observed in human divers.

Incidental capture, or ‘bycatch’ in fishing gear is a major global threat to sea turtle populations. A recent study showed that underwater entrapment in fishing gear followed by rapid decompression may cause gas bubble formation within the blood stream (embolism) and tissues leading to organ injury, impairment, and even mortality in some bycaught individuals. We analyzed data from 128 capture events using logistic and ordinal regression to examine risk factors associated with gas embolism in sea turtles captured in trawls and gillnets. Likelihood of fatal decompression increases with increasing depth of gear deployment. A direct relationship was found between depth, risk and severity of embolism, which has not been previously demonstrated in any breath-hold diving species. For the trawl fishery in this study, an average trawl depth of 65 m was estimated to result in 50% mortality in by-caught turtles throughout the year. This finding is critical for a more accurate estimation of sea turtle mortality rates resulting from different fisheries and for devising efforts to avoid or minimize the harmful effects of capture.

Heart-rate ( f H ) changes during diving and exercise are well documented for marine mammals, but changes in stroke volume (SV) and cardiac output (CO) are much less known. We hypothesized that both SV and CO are also modified following intense exercise. Using transthoracic ultrasound Doppler at the level of the aortic valve, we compared blood flow velocities in the left ventricle and cardiac frequencies during rest and at 1, 3 and 4 min after a bout of exercise in 13 adult bottlenose dolphins (Tursiops truncatus, six male and seven female, body mass range 143-212 kg). Aortic cross-sectional area and ventricle blood velocity at the aortic valve were used to calculate SV, which together with f H provided estimates of left CO at rest and following exercise. f H and SV stabilized approximately 4-7 s following the post-respiratory tachycardia, so only data after the f H had stabilized were used for analysis and comparison. There were significant increases in f H , SV and CO associated with each breath. At rest, f H , SV and CO were uncorrelated with body mass, and averaged 41±9 beats min , respectively. One minute following high intensity exercise, the cardiac variables had increased by 104±43%, 63±11% and 234±84%, respectively. All variables remained significantly elevated in all animals for at least 4 min after the exercise. These baseline values provide the first data on SV and CO in awake and unrestrained cetaceans in water.

In recent decades, biologists have sought to tag animals with various sensors to study aspects of their behavior otherwise inaccessible from controlled laboratory experiments. Despite this, chemical information, both environmental and physiological, remains challenging to collect despite its tremendous potential to elucidate a wide range of animal behaviors. In this work, we explore the design, feasibility, and data collection constraints of implantable, near-infrared fluorescent nanosensors based on DNA-wrapped single-wall carbon nanotubes (SWNT) embedded within a biocompatible poly(ethylene glycol) diacrylate (PEGDA) hydrogel. These sensors are enabled by Corona Phase Molecular Recognition (CoPhMoRe) to provide selective chemical detection for marine organism biologging. Riboflavin, a key nutrient in oxidative phosphorylation, is utilized as a model analyte in in vitro and ex vivo tissue measurements. Nine species of bony fish, sharks, eels, and turtles were utilized on site atOceanografc in Valencia, Spain to investigate sensor design parameters, including implantation depth, sensor imaging and detection limits, fluence, and stability, as well as acute and long-term biocompatibility. Hydrogels were implanted subcutaneously and imaged using a customized, field-portable Raspberry Pi camera system. Hydrogels could be detected up to depths of 7 mm in the skin and muscle tissue of deceased teleost fish (Sparus aurata and Stenotomus chrysops) and a deceased catshark (Galeus melastomus). The

There is growing concern about the spreading of human microorganisms in relatively untouched ecosystems such as the Antarctic region. For this reason, three pinniped species (Leptonychotes weddellii, Mirounga leonina and Arctocephalus gazella) from the west coast of the Antartic Peninsula were analysed for the presence of Escherichia spp. with the recovery of 158 E. coli and three E. albertii isolates. From those, 23 harboured different eae variants (α1, β1, β2, ε1, θ1, κ, ο), including a bfpA-positive isolate (O49:H10-A-ST206, eae-k) classified as typical enteropathogenic E. coli. Noteworthy, 62 of the 158 E. coli isolates (39.2%) exhibited the ExPEC status and 27 (17.1%) belonged to sequence types (ST) frequently occurring among urinary/bacteremia ExPEC clones: ST12, ST73, ST95, ST131 and ST141. We found similarities >85% within the PFGE-macrorrestriction profiles of pinniped and human clinic O2:H6-B2-ST141 and O16:H5/O25b:H4-B2-ST131 isolates. The in silico analysis of ST131 Cplx genomes from the three pinnipeds (five O25:H4-ST131/PST43-fimH22-virotype D; one O16:H5-ST131/PST506-fimH41; one O25:H4-ST6252/PST9-fimH22-virotype D1) identified IncF and IncI1 plasmids and revealed high core-genome similarities between pinniped and human isolates (H22 and H41 subclones). This is the first study to demonstrate the worrisome presence of human-associated E. coli clonal groups, including ST131, in Antarctic pinnipeds.

In dolphinaria, dolphins and their trainers build relationships and bonds due to the nature, closeness and repeatability of their interactions, hence training sessions are deemed appropriate to evaluate dolphin welfare. Qualitative Behavioural Assessments (QBAs) have been used to study human–animal relationships and are included in several animal welfare assessments. We introduce here the first QBA aiming to analyse dolphin–trainer interactions during training sessions in terms of dolphin welfare. Our results show that “Willingness to Participate” (WtP) was significantly associated to six other parameters: high-speed approach, high level of excitement, high number of positive responses to trainers’ signals, rare refusal to perform certain behaviours, rare spontaneous departure behaviours and fast approach once the trainer entered into the pool. Therefore, we suggest using WtP and those “alerting factors” when assessing dolphin–trainer interactions under professional care. The evaluation should also consider the time of day, the dolphin’s age, trainer experience level, the nature of the training sessions and to a lesser extent the sex of the dolphins, as contributing and modulating factors. The factor eye contact has been used in various HARs studies and has been proven to be a valid indicator in welfare research works, hence potentially deserving further research. These results demonstrate the pertinence and feasibility of this approach, the ease of use of this methodology by professionals in zoo/aquarium settings and the appropriateness of the obtained results within the holistic frame of animal welfare.

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