Noise-induced temporary threshold shifts following intermittent underwater sound exposure in the aquatic Eastern painted turtle ( Chrysemys picta picta )

Aquatic turtles can incur underwater hearing loss—or temporary thresholds shifts (TTSs)—upon exposure to continuous broadband and narrowband sound; a key question is how the turtle ear responds to intermittent sound sources. We exposed three Eastern painted turtles (Chrysemys pica pica) to 20 min of underwater 400 Hz 1/6-octave narrowband noise at 4 duty cycles (25–75% intermittent; 100% continuous) and two exposure amplitudes [cumulative sound exposure levels (SELcum): 156–172 dB re 1 μPa2s]. Underwater auditory evoked potential measurements at 570 Hz demonstrated significant shifts ranging 6.4–27.4 dB, with lower TTS after intermittent exposures, compared to continuous. Although turtles experienced TTS at all duty cycles tested, recovery intervals within the intermittent exposures appeared to limit TTS growth, as observed in mammals. Thresholds shifts for intermittent noise were lower than shifts observed and predicted for 100% duty cycle exposures of the same SELcum, suggesting SELcum may overestimate TTS in aquatic turtles. Faster recovery rates occurred after 75% and 100% duty cycle exposures, compared to 25% and 50%, likely because of the greater TTS induced. We illustrate observed shifts may have significant impacts on detection distances of biologically relevant sounds, highlighting the importance of noise management for this threatened taxon.