Simultaneous operation of mobile acoustic recording systems off the Washington coast for cetacean studies

Acoustic monitoring of cetaceans was conducted using two buoyancy-driven AUVs in a deep-water canyon north of the Navy's QUTR range off the Washington coast in April 2015. The two AUVs operated were the acoustically-equipped QUEphone, which is an APEXTM-based acoustic profiler float from Teledyne Webb, and the SeagliderTM from Kongsberg. A passive acoustic monitoring device, WISPR, from Embedded Ocean Systems (EOS) was installed on both AUVs. With one 512GB CF card and level-2 Free Lossless Audio Codec (FLAC), WISPR recorded sound continuously for 12 days at a 125 kHz sampling rate with 16-bit resolution. The Sealider's record showed high levels of flow noise below 100 Hz during ascent, 16 dB higher than during the descent. The Seaglider's CTD generated 1-sec long line noise at 53.37 kHz at 5 to 10 sec intervals, while the Seaglider's mass shifter generated 3-sec long band-limited noise below 10 kHz. The QUEphone's acoustic record was generally quieter than the Seaglider primarily due to the fact that it is nearly stationary platform with less mechanical and electrical components to generate system noise. Despite higher system noise levels, the Seaglider detected twice as many calls/clicks resulting from its ability to actively stay in the target area where the population density of marine mammals was higher, while the QUEphone drifted away from the target area with the prevailing ocean currents.