Temporary threshold shifts in the Eastern painted turtle (Chrysemys picta picta) in response to narrowband underwater noise exposures.

Abstract

Sound is important to many turtle species, emphasizing the need for data-driven predictive models of acoustic impacts of noise pollution. Freshwater turtles experience temporary threshold shifts (TTSs) and data of the specific frequencies and duration inducing hearing loss are critical for TTS modeling. Three adult female Eastern painted turtles (Chrysemys picta pica) were exposed to 1/6-octave-narrowband noise centered at 200 or 400 Hz at varying durations and amplitudes (received sound exposure levels, 136-174 dB re 1 μPa2 s). Underwater auditory thresholds were measured at each band's center frequency and 1/2 octave above these frequencies using auditory evoked potential methodology. A comparison of post-exposure to control thresholds revealed that all turtles experienced TTS at all four test frequencies. Turtles showed greater susceptibility to the 400-Hz centered narrowband, a frequency of higher auditory sensitivity. Greater TTS and a lower TTS onset was observed at 570 Hz compared to 400 Hz, revealing an upward frequency shift in TTS compared to the exposure frequencies. Auditory sensitivity recovered within <1 h or by two days post-exposure, but one turtle showed TTS lasting multiple weeks. Narrowband TTS growth aligned with broadband empirical models, suggesting TTS predictions may be similar for these two noise types.