Scientists have detected high frequency irregular heartbeats or heart arrhythmias in bottlenose dolphins and Weddell seals during their deepest dives.

This shows that exercising while holding their breath remains a physiological challenge for marine mammals despite their remarkable adaptations to aquatic life.

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"The heart is receiving conflicting signals when the animals exercise intensely at depth, which often happens when they are starting their ascent. We're not seeing lethal arrhythmias, but it is putting the heart in an unsteady state that could make it vulnerable to problems," said lead author Terrie Williams, professor of ecology and evolutionary biology at University of California-Santa Cruz.

Researchers discovered that heart rates of diving animals varied with both depth and exercise intensity. Heart rates alternate rapidly between periods of bradycardia and tachycardia. Cardiac arrhythmias occurred in more than 70 percent of deep dives.

In conducting the new study, experts developed a monitoring device to record heart rate, swimming stroke frequency, depth, and time throughout the dives of trained bottlenose dolphins diving in pools or open water, as well as free-ranging Weddell seals swimming beneath the ice in McMurdo Sound, Antarctica.

The new research has implications for better understanding stranding events involving deep-diving marine mammals like beaked whales.

Researchers noted the behaviors related with cardiac anomalies (increased physical exertion and rapid ascent from depth, among others) are similar to those involved in the flight response of beaked whales and blue whales exposed to shipping noise and mid-frequency sonars.

The study also stated these findings are important to humans. The mammalian dive response or dive reflex also occurs in humans and other terrestrial animals and is triggered when the face contacts cold water.

Details of the study were published in Nature Communications.

Tagsbottlenose dolphins, marine mammal, irregular heartbeat, arrhythmias