Investigating bottlenose dolphin physiology using near-infrared spectroscopy

Cetaceans spend considerable periods of time underwater, but much about the physiological response of these animals during a dive remains unknown. We present an approach that combines near-infrared spectroscopy (NIRS) with kinematic measurements to investigate bottlenose dolphin hemodynamics in managed settings during voluntary breathing at the surface, diving to a submerged target, and free swimming. For all conditions, oxygenated hemoglobin (HbO) initially increased following respiration as oxygen saturation increased and then decreased until the following breath. Deoxygenated hemoglobin (HbR) remained relatively steady during shorter respiration periods (near surface and swimming dives) but declined during the longer breath-holds and swimming dives. This was also seen in the calculated tissue saturation index (TSI), with up to an 8.9% decrease during extended breath-holds. The approach presented here provides new insights into the physiological responses of free-swimming animals and is an important step towards making these measurements from animals in the wild.