Hearing in Sea Otters (Enhydra lutris): Audible Frequencies Determined from a Controlled Exposure Approach

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The sea otter (Enhydra lutris) is an amphibious marine mammal that is vulnerable to coastal anthropogenic disturbance. Effective management of noise-generating activities within sea otter habitats requires information about hearing that is presently unavailable for this species. As an initial step toward describing the auditory capabilities of sea otters, we used a controlled exposure approach to conservatively estimate the aerial frequency range of hearing in four captive individuals. The study was designed to determine which frequencies were audible to each animal rather than to quantify auditory sensitivity. To this end, the sea otters were intermittently exposed to relatively highamplitude tones between 0.063 and 45.3 kHz— and to blank “control” events—during periods of sustained rest. Positive responses to both the sound exposure trials and the control trials were scored by experimentally blind observers and used to determine statistically reliable detections at each frequency. The widest confirmed hearing range measured for the sea otters was 0.125 to 32 kHz. Our results indicate that sea otters can detect a broad range of airborne sounds, similar to many terrestrial carnivores that have been studied. These are the first hearing measurements obtained for this species, and the results are relevant to improving understanding of sea otter acoustic communication, evolutionary biology, and behavioral ecology, as well as in supporting ongoing conservation efforts. This method can be adapted to examine the acoustic detection capabilities of species for which little data are available and for which conventional audiometry may prove challenging.