Acoustic detection, localization, and tracking of vocalizing humpback whales on the U.S. Navy's Pacific Missile Range Facility

Abstract

A subset of the 41 deep water broadband hydrophones on the U.S. Navy's Pacific Missile Range Facility (PMRF) to the northwest of Kauai, Hawaii was used to acoustically detect, localize, and track vocalizing humpback whales as they transited through this offshore range. The focus study area covers 960 square kilometers of water (water depths greater than 300 m and more than 20 km offshore). Because multiple animals vocalize simultaneously, novel techniques were developed for performing call association in order to localize and track individual animals. Several dozen whale track lines can be estimated over varying seasons and years from the hundreds of thousands of recorded vocalizations. An acoustic model was used to estimate the transmission loss between the animal and PMRF hydrophones so that source levels could be accurately estimated. Evidence suggests a Lombard effect: the average source level of humpback vocalizations changes with changes in background noise level. Additionally, song bout duration, cue (call) rates, swim speeds, and movement patterns of singing humpback whales can be readily extracted from the track estimates. [This work was supported by Commander U.S. Pacific Fleet, the Office of Naval Research, and Living Marine Resources.]