Marine Mammal Active Sonar Test 2004 (MAST 2004)

Abstract

The Marine Mammal Active Sonar Test was conducted in January 2004 off the central California coast during the gray whale migration. The purpose of the test was to collect data to significantly advance active sonar detection, classification, and tracking of marine mammals out to ranges of 1 mile. The R/V New Horizon was moored in the migration path. Two different sonar systems operating between 210 and 220 dB were deployed off the vessel, the IMAPS phased array sonar system that operates from 20–30 kHz and the MAST mechanical system that uses rotating parabolic transducers operating from 30 to 40 kHz. Marine mammal observers were deployed on the bluffs overlooking the experiment and aboard the New Horizon. The observers tracked the whales using electronic theodelites, providing ground truth for the sonar systems. They also looked for any severe reactions from the animals, and called for a shutdown if any marine mammals were observed within 100 m of the sonar. Here, we discuss the experiment and the results to date, including any reaction of the whales to the sonar system. We will also touch on the legal battle to conduct the experiment, and lessons learned.