AFSC/MML: Acoustics short-term passive monitoring using sonobuoys in the Gulf of Alaska, Bering, Chukchi, and Western Beaufort Seas, Summer 2007-2018

The Marine Mammal Laboratory (MML) has conducted passive acoustic monitoring in the Gulf of Alaska, Bering, Chukchi, and Western Beaufort Seas to determine spatio-temporal distribution of marine mammals as well as environmental and anthropogenic noise. Species and sounds detected on sonobuoys include fin, blue, bowhead, humpback, killer, gray, minke, sperm, beluga, sei, and North Pacific right whales, walrus, ribbon and bearded seals, fish, and seismic airguns. This short-term passive acoustic monitoring was also used to locate vocalizing species of interest for photo-identification, tagging, and behavioral studies. Recordings are available since 2007 in the Bering Sea, since 2010 in the Chukchi and Beaufort Seas, and in 2013 and 2015 in the Gulf of Alaska. Both omnidirectional and DiFAR sonobuoys have been used. In one year (2009), sonobuoys were deployed opportunistically from an aerial survey plane. All sonobuoys were provided by the United States Navy (Naval Operational Logistics Support Center, Naval Surface Warfare Center, Crane Division, and the Office of the Assistant Secretary of the Navy).

The purpose of these sonobuoy deployments is to assess short-term presence, distribution, and relative abundance of marine mammals in the Gulf of Alaska, Bering, Chukchi, and Beaufort Seas, and also to locate vocalizing species of interest for photo-identification, tagging, and behavioral studies.

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Excel and Matlab files

In previous years, some information was not always recorded including specific sonobuoy information (e.g. Manufacturer, Year, Settings, etc.) or deployment information (e.g. time, water depth, channel settings, etc.).

Not applicable.

Sonobuoy recordings are reviewed upon returning from the survey. Questionable acoustic detections are analyzed, and if necessary, clips are sent to colleagues for confirmation or identification.

IT Security and Contingency Plan for the system establishes procedures and applies to the functions, operations, and resources necessary to recover and restore data as hosted in the Western Regional Support Center in Seattle, Washington, following a disruption.

A sonobuoy is a free-floating, expendable, short-term passive acoustic listening device that transmits signals in real time via VHF radio waves to a receiver on a vessel or aircraft. The hydrophone is suspended down from the surface float at a programmable depth. For the majority of deployments, modifications were made by tying or taping sections of the sonobuoy housing to prevent the main wire spool from deploying; the resulting deployment depth was then 24 m. Additional modifications involved replacement of the display battery. Three types of sonobuoys were used: omnidirectional only, DiFAR only, and programmable DiFAR/Omnidirectional. DiFAR (Directional Frequency Analysis and Recording) capable sonobuoys transmit signal bearing information along with the acoustic signal. If two or more DiFAR sonobuoys are deployed, cross-fixes can be obtained on a calling animal to determine its location. When in DiFAR mode, the maximum frequency is limited to 2.5 kHz; the omni-directional sonobuoys were deployed occasionally in omnidirectional mode to achieve full bandwidth when bearing information was not needed. The methods that follow apply from 2009 on; prior to 2009 a variety of equipment and methods were used (see www.data.boem.gov/PI/PDFImages/ESPIS/5/5243.pdf for further details). The signals transmitted from the sonobuoys were received by one of two antennas, an omnidirectional and a directional (Yagi) antenna. Both antennas were placed in the crow’s nest of the vessel with the directional antenna facing astern. The directional antenna was used primarily during transit when the sonobuoy behind the vessel, and the omnidirectional antenna was used for monitoring multiple sonobuoys simultaneously, or when the boat was idling at station. A switch located in the bridge next to the acoustic station was used to alternate between antennas depending on the direction of travel. The signals received by the shipboard antennas were pre-amplified (15dB; PV160VDA, Advanced Receiver Research, Burlington, VT), before being sent via cabling to three G39WSBe WinRadio sonobuoy receivers, then inputted into a MOTU brand Ultralite mk3 multi-channel external soundcard. The soundcard digitized the signal at a sampling rate of 48 kHz. The external soundcard was connected to a laptop computer where the recordings were monitored in real-time and simultaneously recorded to an external hard drive using ISHMAEL (Mellinger 2001) software. Directional bearing information of calls was obtained using DiFAR demultiplexing software and a custom MATLAB interface (Greeneridge Sciences, Inc. and Mark McDonald, Whale Acoustics). A GPS feed into the computer provided the ship’s position every minute, as well as the sonobuoy deployment location information, and time. A custom tracking and plotting program implemented in MATLAB (Catherine Berchok, MML) allowed for real-time plotting of the vessel and sonobuoy locations, as well as bearing and location coordinates of calling whales. Monitoring occurred in real time 24/7, with the majority of sonobuoys deployed every three hours during ship transits. Analysis of sonobuoy data was undertaken primarily during the cruise. An acoustic technician monitored the scrolling spectrograms of the recordings from each sonobuoy aurally as well as visually, and noted the species detected during its deployment, these are included in the data as detected (1), not-detected (0), or possibly detected (2). Further information can be obtained via the following publications: Crance et al. 2017, and Rone et al. 2012.