Dolphins can slow down their heartbeat before diving, and they do it “consciously”, depending on how long and deep dive is planned.
A team of scientists led by Andreas Fahlman of the Spanish Oceanographic Foundation conducted experiments with three captive bottlenose bottlenose dolphins. The animals were taught in advance to hold their breath: depending on the command of the person, they stopped breathing for a short (for themselves) time, or for a long time, or for an arbitrary interval of their choice. After giving the command, the authors tracked their breathing and heartbeat.
It was found that just before the dolphins stopped breathing, or together with the very stop, their heart rate slowed down. Moreover, the deceleration of the rhythm occurred faster and stronger when the dolphins prepared for a long air retention. “Dolphins can vary their heart rate in the same way you and I can control our breathing,” says Andreas Fahlman. “This allows oxygen to be retained longer and reduces many of the dive-related risks, such as developing decompression.”
Male with ECG sensors attached / © Mirage, Siegfried and Roy’s Secret Garden and Dolphin Habitat
Details of the work are given in an article published in the journal Frontiers in Physiology. Fahlman himself adds that in recent years, decompression and similar problems have been found in free-range dolphins with an alarming frequency. They are associated with human economic activity, which fills the oceans with “acoustic debris”. Perhaps this eternal and loud (for them) noise interferes with the ability of dolphins to “plan” their dives and slow down their heart rate in advance.