A new study has found a more reliable way to estimate how much energy dolphins burn while they swim, which could have important implications for understanding dolphin physiology and how human disturbance impacts them.
A dolphin's survival often hinges on whether it can crank up the speed - whether foraging for prey or evading predators and ship strikes.
But if their manoeuvres regularly burn more kilojoules than they take, they can deplete reserves vital for growth, health, and reproduction.
Being able to estimate these energy costs of locomotion (COL) to determine where that tipping point may be is essential for understanding dolphin physiology and ecology and the impacts of human disturbance on them.
But measuring this in the wild is extremely difficult and has previously been estimated based on the number of fluke (tail) strokes per minute, which is an imprecise measure of swimming effort, since not all fluke strokes are the same size.
Now, researchers have found that they can use movement tags to determine their overall dynamic body acceleration (ODBA) - an integrated measure of all motions a dolphin makes during swimming - to get a much more reliable measure of how hard dolphins are actually working.
"Researchers have used movement tags to measure ODBA in other species, but this is the first published study calibrating ODBA with energy expenditure in multiple dolphins," said first author Dr Austin Allen, from Nicholas School of the Environment at Duke University in the U.S.
Published in Journal of Experimental Biology, the team conducted swim trials with six trained bottlenose dolphins at Dolphin Quest (a facility on Oahu, Hawaii) using the delightfully named pneumotachometer - a non-invasive device placed over the blow hole to measure the flow rate of gases during breathing - to measure oxygen consumption.
Researchers measured each dolphin while at rest and then immediately after swimming an 80-metre lap across a lagoon, all while non-invasive bio-logging tags were also recording their three-dimensional body movements.
By analysing this data in combination, a pattern began to emerge: when the dolphin accelerated, their oxygen consumption increased too.
"There was some individual variation, but, overall, the results showed significant correlation between oxygen consumption and body acceleration, which suggests ODBA can be a reliable proxy for COL," says Allen.
"Working with dolphins in zoos or aquariums is allowing us to use data we've already collected using these tags in the field to evaluate the COL in wild populations."
The researchers suggest that similar approaches could also be applied to other air-breathing aquatic mammals, like whales.
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