Diving marine mammals take deep prey plunges to heart

Weddell seals (Leptonychotes weddellii) and bottlenosed dolphins (Tursiops truncates) might be expert divers. But their hearts don’t stay steady at depth, instead beating irregularly when the animals plunge underwater to chase prey.

Researchers outfitted the animals with sensors to measure their heart rates while diving more than 200 meters beneath the ocean surface. Because these marine mammals have evolved for diving, scientists expected to see the animals’ heart rates drop to conserve oxygen. Instead, the seals and dolphins developed irregular heartbeats — often alternating fast and slow rhythms — in 73 percent of dives.

Separate neural circuits govern the heart’s response to depth and exertion, and mixed messages may drive the animals’ weird heart rates. The findings, published January 16 in Nature Communications, could give clues to what’s happening to human triathletes’ hearts when the racers hit the water.