Hearing thresholds of swimming Pacific bluefin tuna Thunnus orientalis
Pacific bluefin tuna (Thunnus orientalis) is a highly migratory, commercially valuable species potentially vulnerable to acoustic noise generated from human activities which could impact behavior and fitness. Although significant efforts have been made to understand hearing abilities of fishes, the large size and need to continuously swim for respiration have hindered investigations with tuna and other large pelagic species. In this study, Pacific bluefin tuna were trained to respond to a pure tone sound stimulus ranging 325–800 Hz and their hearing abilities quantified using a staircase psychophysical technique. Hearing was most sensitive from 400 to 500 Hz in terms of particle motion (radial acceleration −88 dB re 1 m s−2; vertical acceleration −86 dB re 1 m s−2) and sound pressure (83 dB re 1 μPa). Compared to yellowfin tuna (Thunnus albacares) and kawakawa (Euthynnus affinis), Pacific bluefin tuna has a similar bandwidth of hearing and best frequency, but greater sensitivity overall. Careful calibration of the sound stimulus and experimental tank environment, as well as the adoption of behavioral methodology, demonstrates an experimental approach highly effective for the study of large fish species in the laboratory.