Threshold of hearing for swimming Bluefin tuna (Thunnus orientalis)

Abstract

Hearing thresholds for three pairs of 1 m long Pacific bluefin tuna (Thunnus orientalis) were measured utilizing operant conditioning procedure with a food reward and a staircase psychophysical technique. Fish, swimming at 1–4 m/s, quickly learned to approach the feed when they heard a sound. Measurements were made at the Tuna Research and Conservation Center (Stanford University) in a 9.14 m diameter, 1.65 m deep indoor cylindrical tank. The acoustic stimulus was produced by radially oriented piezoelectric line sources centered at the bottom of the tank, which produced a circumferentially uniform sound field. The acoustics of the tank was thoroughly characterized for both acoustic pressure and particle motion using hydrophones and two neutrally buoyant accelerometers with response axes oriented in the radial and vertical directions. Thresholds, expressed in terms of pressure and particle acceleration, were obtained at six sinusoidal frequencies between 325 Hz and 800 Hz, a range that was limited by source and tank acoustics. The lowest mean threshold for the three fish pairs, expressed in terms of acoustic pressure, was 83 dB re 1 µPa at 500 Hz. [Work supported in part by ONR/CNR Challenge Grant: “Mitigation of flow noise effects by fish.”]