Extended aquarium opening hours during tourist rush season cause temporary threshold shifts in an Indo-Pacific humpback dolphin

Aquariums worldwide have undergone substantial growth in both scale and number in recent decades. However, the issue of anthropogenic underwater noise pollution within these facilities and its impact on cetaceans has been largely neglected. Here, we examined underwater sound levels in an aquarium during both the tourist rush season and the off-season, alongside the corresponding audiogram, of an Indo-Pacific humpback dolphin. Results indicated that sound exposure levels during the aquarium’s opening hours were significantly higher than during non-opening hours. Likewise, the daily cumulative auditory-weighted sound exposure level (SEL cw ) during the tourist rush season (180 dB) exceeded the threshold for the onset of temporary threshold shifts (TTS) in humpback dolphins (178 dB). By contrast, the daily SEL cw during the tourist off-season (173 dB) remained below the threshold for the onset of TTS in humpback dolphins. The dolphin audiogram obtained during the tourist rush season revealed an elevated level of 14 ± 11 dB compared to levels observed during the tourist off-season. Approximately 41% of the dolphin’s auditory thresholds exhibited an elevation exceeding 20 dB. The increased frequency of openings, resulting in extended cumulative opening hours during the tourist rush season, led to elevated sound exposure, which induced TTS in the dolphins. The findings underscore the critical need for meticulous control measures, such as tracking cumulative operating hours, and are essential for informing the development of appropriate welfare standards for animals in both captivity and the wild.