Abstract
An array of four hydrophones spaced over 200 m near the shore of San Juan Island, WA, has been used to localize the underwater vocalizations of Southern Resident orca whales. The hydrophones (ITC) have home-built pre-amps and amplifiers and signals are digitized simultaneously by two computers. The system has been calibrated with an underwater speaker (J-9). Automatic call detection is used to activate data logging on one computer and real-time localization on a second that directs a video camera to record the water’s surface at the predicted source location. The system requires about 1 s to detect a call, locate it and redirect the video camera. This is the first report of source levels of social vocalizations of free-ranging Southern Resident orcas. To date (July 2004), 160 orca calls have been localized within 200 m of the center of the array. The average acoustic intensity of these calls is 145 dB re 1 μPa@1 m. The range of intensities is from 137 to 157 dB re 1 μPa@1 m. Complete results including intensity angular distributions with respect to the probable direction of whale travel will be presented. [Work supported by 32 undergraduate researchers over 5 years and the Colorado College Physics Department.]
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