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Dolphins lower their heart rate before diving to conserve oxygen

In a new study published by Frontiers, experts have found that dolphins can slow down their heart rate before diving to conserve oxygen and prevent issues associated with pressure. The research indicates that dolphins and other marine mammals consciously lower their heart rate to match the duration of an upcoming dive. 

“Dolphins have the capacity to vary their reduction in heart rate as much as you and I are able to reduce how fast we breathe,” said Dr. Andreas Fahlman of the Fundación Oceanogràfic in Spain. “This allows them to conserve oxygen during their dives, and may also be key to avoiding diving-related problems such as decompression sickness, known as ‘the bends.'”

The findings provide unprecedented insight into how marine mammals conserve oxygen and adjust to pressure while diving.

The study was focused on three male bottlenose dolphins that were trained to hold their breath for different lengths of time upon instruction. 

“We trained the dolphins for a long breath-hold, a short one, and one where they could do whatever they wanted,” explained Dr. Fahlman. “When asked to hold their breath, their heart rates lowered before or immediately as they began the breath-hold. We also observed that the dolphins reduced their heart rates faster and further when preparing for the long breath-hold, compared to the other holds.”

It is important for experts to understand how marine mammals are able to dive safely for long periods of time in order to help prevent health risks associated with human-caused sound disturbances. 

“Man-made sounds, such as underwater blasts during oil exploration, are linked to problems such as the bends in these animals,” said Dr. Fahlman.

“If this ability to regulate heart rate is important to avoid decompression sickness, and sudden exposure to an unusual sound causes this mechanism to fail, we should avoid sudden loud disturbances and instead slowly increase the noise level over time to cause minimal stress. In other words, our research may provide very simple mitigation methods to allow humans and animals to safely share the ocean.”

It has been difficult for scientists to analyze changes in dolphin physiology during dives due to the practical challenges of measuring relevant functions such as heart rate and breathing.

“We worked with a small sample size of three trained male dolphins housed in professional care,” said Dr. Fahlman. “We used custom-made equipment to measure the lung function of the animals, and attached electrocardiogram (ECG) sensors to measure their heart rates.”

Andy Jabas is a dolphin care specialist at Siegfried & Roy’s Secret Garden and Dolphin Habitat at the Mirage, Las Vegas, which is the home of the dolphins observed for this study.

“The close relationship between the trainers and animals is hugely important when training dolphins to participate in scientific studies,” said Jabas.

“This bond of trust enabled us to have a safe environment for the dolphins to become familiar with the specialized equipment and to learn to perform the breath-holds in a fun and stimulating training environment. The dolphins all participated willingly in the study and were able to leave at any time.”

The research is published in the journal Frontiers in Physiology.

By Chrissy Sexton, Staff Writer

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