Estimating received levels for acoustically tracked whales from Navy mid-frequency active sonar

Abstract

Multi-channel passive acoustic data were collected from bottom-mounted hydrophones off the coast of Kauai, HI at the U.S. Navy Pacific Missile Range Facility’s instrumented range. In February 2017, data were recorded during the Submarine Command Course (SCC) training event that included mid-frequency active sonar (MFAS). Data were post-processed for minke whale (Balaenoptera acutorostrata) vocalizations and MFAS with automated detection, classification, and localization algorithms. Semi-automated processes were used to perform spatio-temporal associations of whale localizations to create individual whale tracks and to associate localized MFAS transmissions with positional data from multiple ships. For each whale track, the received level from each MFAS transmission was estimated using a parabolic equation propagation model that statistically represented the uncertainty of whale location and depth. Exposures were accumulated over the duration of each whale track to estimate the cumulative sound exposure level (cSEL; dB re: 1μPa2s). Twenty-three minke whales were exposed to MFAS during the SCC; the maximum exposure was 169.8 dB cSEL, and the minimum distance to a ship transmitting MFAS was 4.8 km. Currently, statistical analyses of track kinematics and call characteristics are being conducted to quantify any significant changes between animal track kinematics with and without MFAS training presence.