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How do some dolphins dive deeper than others?

Scientists have been investigating how different populations of the same species of dolphin have a wide range of diving abilities. The experts have developed a new theory that lung architecture and the management of blood flow play a major role in the hunting depths of dolphins.

Bottlenose dolphin populations are typically close to land in shallow coastal environments and dive of less than 10 meters for their prey. However, other groups such as the Bermudian population dive to depths of around 400 meters, and even 1000 meters on some occasions.

Dr. Andreas Fahlman of the Fundación Oceanográfic in Spain led two separate studies to gain a better understanding of how dolphins of a single species could dive so differently.

“We wanted to measure what kind of differences are responsible for these huge variations,” said Dr. Fahlman. “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.”

In the first study, deep diving dolphins were found to have a greater oxygen storage capacity compared to bottlenose dolphins in Florida that dive in shallow water. While this capacity would enable them to dive for longer durations, there were no differences in the lung mechanics or metabolic rates between the two populations.

“This was unexpected, as past studies have suggested that compression of the lungs was the main adaptation to avoid taking up excessive nitrogen at depth and getting the bends,” said Dr. Fahlman. “The lack of differences in the lungs between the shallow and deep divers suggest that the dolphins may use other means to avoid diving related problems.”

In a second study, the team estimated how different populations may manage gas exchange according to their diving lifestyles. A model developed by the experts indicated that, when comparing known parameters of how much oxygen storage would be required, the deep diving dolphins would exceed their calculated dive limits.

“The results indicated that the deep diving population would need to keep an elevated heart rate, not only during surface intervals, but also during shallow dives in-between deep dives to allow sufficient restoration of oxygen stores,” said Dr.Fahlman.

“Keeping the blood flow elevated between deep foraging dives helps reduce time spent at the surface and enhances recovery time. On the other hand, during deep dives, the dolphins would need to direct blood flow through collapsed regions of the lung, allowing some exchange of oxygen and carbon, while preventing the exchange of nitrogen. Thus, the dolphins may have a way to manage the level of nitrogen they absorb and thereby preventing the bends.”

“This hypothesis provides new and exciting research opportunities to understand how mammals can dive to extreme breaths on a lung full of air without any of the related problems that humans experience. However, our dataset is limited, and further studies should be done on other deep diving dolphin populations to determine if there are similar physiological requirements for deep diving.”

The research is published in the journal Frontiers in Physiology.

By Chrissy Sexton, Staff Writer

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