High heart rates in hunting porpoises

The impressive breath-hold capabilities of marine mammals are facilitated by both enhanced O2 stores and reductions in the rate of O2 consumption via peripheral vasoconstriction and bradycardia, coined the dive response. Many studies have focused on the extreme role of the dive response in maximizing dive duration in marine mammals, but few have addressed how these adjustments may compromise the capability to hunt, digest and thermoregulate during routine dives. Here we use DTAGs which record heart rate together with foraging and movement behaviour to investigate how O2 management is balanced between the need to dive and forage in five wild harbour porpoises that hunt thousands of small prey daily during continuous shallow diving. Dive heart rate was moderate (median minimum 47-69 bpm) and relatively stable across dive types, dive duration (0.5-3.3 min), and activity. A moderate dive response, allowing for some perfusion of peripheral tissues, may be essential for fuelling the high fiel...