Presenter: Andria Salas (Woods Hole Oceanographic Institution)

Description:
Anthropogenic noise is a primary feature of coastal and pelagic soundscapes, creating an additional stressor that can compromise individual survival and fitness. Understanding how this stressor affects marine taxa is vital given increasing offshore energy development and other activities producing substantial sound. One acoustic impact is a reduction in hearing sensitivity. Temporary threshold shifts (TTS) after noise exposure have been measured in some fishes and marine mammals, and data on sound exposure levels (SELs) that induce TTS are needed to estimate potential impacts and support development of noise criteria guidelines to manage this stressor. The absence of TTS studies in Testudines has led to a stark data gap for endangered sea turtles, and aquatic turtles more generally. We conducted underwater TTS experiments on two species of freshwater turtles (Trachemys scripta elegans and Chrysemys picta), providing an initial baseline to estimate TTS onset in sea turtles. We first established individual underwater hearing sensitivity using auditory evoked potentials, and both species had lowest thresholds to tones 400–⁠600 Hz. We next measured hearing thresholds at 400 or 600 Hz after control conditions and after exposure to broadband noise (50–⁠1000 Hz) that varied in duration and amplitude. We tested the occurrence of TTS after exposure to SELs ranging 152–⁠193 dB re 1 µPa²s across both species, providing data to generate a predictive model of TTS occurrence. We observed clear evidence of TTS in both species, with shifts up to 40 dB re 1 µPa. Hearing thresholds always returned to initial sensitivity following a recovery period. Preliminary analyses show TTS onset for both species occurring much lower than criteria currently used to predict TTS in sea turtles (200 dB re 1 µPa²s). These results provide the first evidence of underwater noise-induced hearing loss in Testudines, and suggest turtles may be more sensitive to sound than previously understood.