Comparable auditory sound pressure level (SPL) and sound intensity level(SIL) threshold curves were determined in air and under water in Ranacatesbeiana. Threshold curves were determined using chronic metal electrodeimplants which detected multi-unit responses of the torus semicircularis toincident sound. In terms of SPL, hearing thresholds in water and air aresimilar below 0.2 kHz. Above 0.2 kHz, the sensitivity under water falls of fat about 16 dB/octave to reach an average loss of about 30 dB above 0.4 kHz. In terms of SIL, the organism is about 30 dB more sensitive under water than in air below 0.2 kHz and equally sensitive in air and water above 0.4 kHz.The relative merits of the two measures are discussed and an attempt is made to relate the results to morphology of the middle and inner ears. This report is the first to compare aerial and underwater hearing abilities in any organism using electrode implants.
Underwater hearing and communication in the endangered Hawaiian monk seal Neomonachus schauinslandi
