Evoked-potential audiogram variability in a group of wild Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis).

Abstract

Hearing is considered the primary sensory modality of cetaceans and enables their vital life functions. Information on the hearing sensitivity variability within a species obtained in a biologically relevant wild context is fundamental to evaluating potential noise impact and population-relevant management. Here, non-invasive auditory evoked-potential methods were adopted to describe the audiograms (11.2-152kHz) of a group of four wild Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis) during a capture-and-release health assessment project in Poyang Lake, China. All audiograms presented a U shape, generally similar to those of other delphinids and phocoenids. The lowest auditory threshold (51-55dB re 1 µPa) was identified at a test frequency of 76kHz, which was higher than that observed in aquarium porpoises (54kHz). The good hearing range (within 20dB of the best hearing sensitivity) was from approximately 20 to 145kHz, and the low- and high-frequency hearing cut-offs (threshold > 120dB re l μPa) were 5.6 and 170kHz, respectively. Compared with aquarium porpoises, wild porpoises have significantly better hearing sensitivity at 32 and 76kHz and worse sensitivity at 54, 108 and 140kHz. The audiograms of this group can provide a basis for better understanding the potential impact of anthropogenic noise.