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RATE: Respiratory Acoustics To estimate Energy in wild cetaceans

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Reliable breath measurements of wild dolphins

Cetaceans such as dolphins play a major role in the marine ecosystem due to their position as top predators at the head of the food chain. The impact of these roles must be quantified by measuring their energy use in the wild, but this is difficult in such highly mobile animals.

Food and Natural Resources
Fundamental Research

Current techniques for estimating energy use in free-swimming dolphins overestimate measured values by over 200 %. Furthermore, they integrate energy expenditure over time scales that are too long, making it difficult to detect responses to specific events or conditions. This has huge implications for how scientists estimate energy requirements in cetaceans and understand how they respond to stressors like man-made sounds. The EU-funded RATE project produced the first reliable estimates of energy expenditure in managed and free-swimming cetaceans by applying techniques from human medicine to obtain information from respiratory sounds. This research was undertaken with the support of the Marie Skłodowska-Curie Actions programme. Lung function tested when swimming In laboratory-type environments, researchers can measure different parameters of the respiratory system, but there have been few to no measurements of breath volume in free-ranging animals. “We wanted to develop a technique to estimate how much air wild dolphins exchange when swimming freely,” says Marie Curie research fellow Dr Julie van der Hoop. The project aimed to relate measured respiratory airflow and volume, and recorded sound to estimate the breath volumes of wild dolphins swimming in their natural environment. “This method estimates volume to within 18 % of measured values; compared to humans, where the validity is 15 %,” explains Dr van der Hoop. Researchers combined two state-of-the art technologies. The first being a flow-meter known as a pneumotachometer, which is normally used to test human lung function. An earlier challenge was to adapt it to dolphins as they can exhale 14 times faster than humans. The second technology involved specialised bio-logging tags that record sound and movement, which attach to dolphins right behind the blowhole by suction cups. The project achieved simultaneous respiratory measurements and acoustic recordings of each breath by placing a custom-built pneumotachometer over the blowhole of bottlenose dolphins to record respiratory flow rates and gases. Digital acoustic recording tags (DTAGs) recorded the sound of exhalation and inhalation. Unexpected result Scientists calibrated respiratory flow rates from breath sounds recorded in dolphins and applied them to free-swimming wild dolphins using the DTAGs. This approach provided reliable estimates of airflow and energy use, and researchers assessed changes in respiratory conditions in response to specific events and behaviours. “We have overcome existing limitations for measuring respiratory physiology in free-swimming animals and have improved the resolution of field-metabolic rate estimates from days to seconds. This really revolutionises how energy turnover can be measured in wild marine mammals,” explains Dr van der Hoop. Results revealed how respiratory volume varies with activity and over time, and that on average, volume is not as high as previously assumed. “These findings will have major repercussions for estimating energy turnover by wild cetaceans and for evaluating the costs of human disturbances and the resulting risk of whales developing decompression sickness,” comments project coordinator Prof. Madsen. RATE also shows that science has come a long way from the whaling-era approach to research. “Now we can measure critical physiological parameters for these wild animals in a non-invasive way. We don’t have to kill whales to study them,” Prof. Madsen concludes.

Keywords

RATE, dolphins, energy, cetacean, digital acoustic recording tags (DTAGs), energy expenditure, pneumotachometer, bio-logging

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