Heart Rate Regulation in the Killer Whale

Abstract

Heart rate responses and gas exchange ultimately underlie the diving capacity/foraging ecology of cetaceans, and may well contribute to the morbidity/mortality of whales stranded after exposure to naval sonar. In order to examine cardiac responses in mid‐sized whales, and eventually measure cetacean heart rates in the wild, we applied a digital electrocardiogram (ECG) recorder with a suction cup attachment technique to a 3868 kg killer whale, Orcinus orca. Heart rate during 10‐min spontaneous, voluntary rest periods ( both apneic and eupneic heart rate) ranged from 21 to 82 beats min−1 between eupnea and apnea, was variable during apnea, and averaged 50 ± 3 SD beats min−1, 1.6 × the resting heart rate predicted by Stahl's allometric equation. During trained, stationary submersions of two to three‐min duration, and during one‐min duration, leisurely underwater swims at 0.5 Hz fluke stroke rate, heart rate was 34 ± 5 SD, and 59 ± 4 SD, respectively. Large oscillations in heart rate with rapid return to baseline occasionally occurred under all conditions. The “resting” heart rate of this killer whale was appropriate for its body mass, but probably elevated due to study conditions (non‐fasting). Sub‐surface swimming elicited an increase in heart rate, and voluntary, trained submersions resulted in a dive response with a variable bradycardia. This approach shows promise to further investigate heart regulation in mid‐sized cetaceans and eventually record heart rates of free‐diving whales.Support or Funding InformationONR Award No N000141410404

Standardization of Dolphin Cardiac Auscultation and Characterization of Heart Murmurs in Managed and Free-Ranging Bottlenose Dolphins (Tursiops truncatus)

“…In recent years, initial steps have been taken to develop antemortem diagnostic cardiac tools in an effort to better understand dolphin cardiology. ECG techniques were first described in dolphins in 1970 (40), and comprehensive findings in putatively healthy dolphins were described by Harms et al (41), with additional reports in managed and free-ranging dolphins and other cetaceans in the last two decades (42)(43)(44)(45)(46). Continued research and investigation have laid the foundation for echocardiographic assessment in managed dolphin populations.…”