Visual deprivation induces a stronger dive response in a harbor porpoise.

The dive response allows marine mammals to perform prolonged breath-hold dives to access rich marine prey resources. Via dynamic adjustments of peripheral vasoconstriction and bradycardia, oxygen consumption can be tailored to breath-hold duration, depth, exercise, and even expectations during dives. By investigating the heart rate of a trained harbor porpoise during a two-alternative forced choice task, where the animal is either acoustically masked or blindfolded, we test the hypothesis that sensory deprivation will lead to a stronger dive response to conserve oxygen when facing a more uncertain and smaller sensory umwelt. We show that the porpoise halves its diving heart rate (from 55 to 25 bpm) when blindfolded but presents no change in heart rate during masking of its echolocation. Therefore, visual stimuli may matter more to echolocating toothed whales than previously assumed, and sensory deprivation can be a major driver of the dive response, possibly as an anti-predator measure.