The underwater sound localization acuity of a swimming harbor seal was measured in the horizontal plane. The stimulus was either a double sound (two 6-kHz pure tones lasting 0.5 s separated by an interval of 0.2 s) or a single continuous sound of 1.2 s. Testing was conducted in a 10-m-diameter underwater half-circle with hidden loudspeakers. The animal was trained to swim along the diameter of the half-circle and to change its course towards the sound source right after the signal was given. The seal indicated the sound source by touching its assumed position at the half-circle. The deviation of the seal’s choice from the actual sound source was measured by means of video analysis. In trials with the double sound the seal localized the sound sources with a mean deviation of 2.8° and in trials with the single sound with a mean deviation of 4.5°. In a second experiment minimum audible angles of the animal were determined as a function of frequency (2, 4, 6, 8, and 16 kHz resulting in MAAs of 9.4°, 9.6°, 9.8°, 13.0°, and 13.5°, respectively). Intraspecific differences of the MAA will be presented for five additional harbor seals.
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