Onset, growth, and recovery of in-air temporary threshold shift in a California sea lion (Zalophus californianus)

TitleOnset, growth, and recovery of in-air temporary threshold shift in a California sea lion (Zalophus californianus)
Publication TypeJournal Article
Year of Publication2007
AuthorsKastak, D., Reichmuth C., Holt M. M., Mulsow J., Southall B. L., and Schusterman R. J.
JournalJournal of the Acoustical Society of America
Volume122
Pagination2916-2924
ISBN Number0001-4966
EndNote Rec Number922
Keywordsbehavioural responses, dolphins tursiops-truncatus, duration, hearing thresholds, noise exposure, pinnipeds, single underwater impulses, tones, whales
Abstract

A California sea lion (Zalophus californianus) was tested in a behavioural procedure to assess noise-induced temporary threshold shift (TTS) in air. Octave band fatiguing noise was varied in both duration (1.5-50min) and level (94-133dB re 20mu Pa) to generate a variety of equal sound exposure level conditions. Hearing thresholds were measured at the centre frequency of the noise (2500Hz) before, immediately after, and 24h following exposure. Threshold shifts generated from 192 exposures ranged up to 30dB. Estimates of TTS onset [159dB re (20)mu Pa)(2) s] and growth (2.5dB of TTS per dB of noise increase) were determined using an exponential function. Recovery for threshold shifts greater than 20 dB followed an 8.8 dB per log(min) linear function. Repeated testing indicated possible permanent threshold shift at the test frequency, but a later audiogram revealed no shift at this frequency or higher. Sea lions appear to be equally susceptible to noise in air and in water, provided that the noise exposure levels are referenced to absolute sound detection thresholds in both media. These data provide a framework within which to consider effects arising from more intense and/or sustained exposures. (c) 2007 Acoustical Society of America.