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Dolphins actively slow their heart before diving and may even adjust their heart rate depending on how long they plan to dive, a new study suggests. Posted in Frontiers in physiology, the results provide new insights into how marine mammals conserve oxygen and adapt to pressure while diving.
The authors worked with three male bottlenose dolphins (Tursiops truncatus), specially trained to hold their breath for varying lengths of time on instruction. “We trained the dolphins for a long freedive, a short one and one where they could do whatever they wanted,” says Dr Andreas Fahlman of Fundación Oceanogràfic, Valencia, Spain. “When asked to hold their breath, their heart rate dropped before or immediately upon onset of apnea. We also observed that dolphins reduced their heart rate faster and more when preparing for the long breath-hold, compared to other catches. “.
The results reveal that dolphins, and possibly other marine mammals, can consciously change their heart rate depending on the length of their planned dive. “Dolphins have the ability to vary their reduction in heart rate as much as you and I are able to reduce the speed at which we breathe,” suggests Fahlman. “This allows them to conserve oxygen during their dives and can also be essential in avoiding diving-related problems such as decompression sickness, known as ‘turns’.”
Understanding how marine mammals can safely dive for long periods of time is critical to mitigating the health effects of human-caused noise disturbance on marine mammals. “Man-made sounds, such as underwater explosions during oil exploration, are linked to problems such as ‘turns’ in these animals,” Fahlman continues. “If this ability to regulate the heart rate is important in preventing decompression sickness, and sudden exposure to unusual sound causes this mechanism to fail, we should avoid sudden loud disturbances and instead slowly increase the rate. noise level over time to cause minimal stress. In other words, our research can provide very simple mitigation methods to allow humans and animals to share the ocean safely ”.
The practical challenges of measuring a dolphin’s physiological functions, such as heart rate and breathing, have previously prevented scientists from fully understanding the changes in their physiology while diving. “We worked with a small sample of three trained male dolphins housed in professional care,” says Fahlman. “We used bespoke equipment to measure the animals’ lung function and attached electrocardiogram (ECG) sensors to measure their heart rate.”
“The close relationship between trainers and animals is extremely important when training dolphins to participate in scientific studies,” says Andy Jabas, Dolphin Care Specialist at Siegfried & Roy’s Secret Garden and Dolphin Habitat at The Mirage, Las Vegas , United States, home of the dolphins studied here. “This bond of trust has allowed us to have a safe environment for the dolphins to familiarize themselves with the specialized equipment and to learn to perform the restraints in a fun and stimulating training environment. The dolphins all voluntarily participated in the study and were able to leave at any time.
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