Friday, 10 August 2018

The freediving champions of the dolphin world


July 17, 2018, Frontiers
For the first time, researchers have explored the physiological adaptations that enable different populations of the same species of dolphin to vary in diving ability by almost 1000m. The research, published in two complementary studies in Frontiers in Physiology, compared the lung mechanics and metabolic rates of bottlenose dolphin populations known for their different hunting depths. Using theoretical estimates of gas management, the results support a new hypothesis that lung architecture and the management of blood flow allow the dolphins to access oxygen in the lungs while preventing uptake of nitrogen, thereby avoiding decompression sickness.

Bottlenose dolphin populations are often found close to land in shallow coastal environments, making short, shallow dives of less than 10m for their prey. However, some populations—such as the Bermudian population in this study—frequently dive to depths of up to 400m, and as deep as 1000m on occasion, spending up to 13 minutes underwater in search of food on a single breath.

"How can a single species have such extremely different life styles?" This question motivated Dr. Andreas Fahlman of the Fundación Oceanográfic in Valencia, Spain, who led both studies with his international team. "We wanted to measure what kind of differences are responsible for these huge variations. This allows us to determine how far the physiology can change within a single species and understand the threat that stressors may have on these deep diving dolphins."

Anyone who has previously scuba-dived will know about decompression sickness, commonly known as 'the bends'. This painful and potentially life-threatening condition is caused from surfacing too quickly at the end of a dive. The rapid expansion of nitrogen bubbles—which form in the bloodstream and tissues during the dive—are not given enough time to diffuse from the body naturally during the ascent.

Dolphins run the same risks when diving to great depths. The team measured the physiology of the lungs and energy consumption of several bottlenose dolphins known to make deep dives to understand how these problems are avoided.


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