Reactions of the Porpoise to Ultrasonic Frequencies

Abstract

Porpoises produce a wide range of sounds, possess well-developed sound receptors, lack an olfactory sense (yet successfully hunt their prey under water), and have tremendously developed cerebral temporal lobes. Some implications arising from these facts were studied on 10 bottle-nosed dolphins (Tursiops truncatus) and 2 long-snouted dolphins (Stenella plagiodon) under controlled conditions in large tanks. U. S. naval equipment, capable of producing 20-200,000 cps, at a minimum underwater sound pressure of 4.03 dynes/cm.2 at 4 m. from the transducer, was used to test the porpoises. The range of reaction, as indicated by sudden speed-up in swimming, lies between 100 and 80,000 cps. Frequencies between 100-400 cps. seem particularly irritating to the animals. It is suggested that if porpoises can produced supersonic sounds (a matter as yet uninvestigated) they may navigate and hunt by ecolocation, as do bats.