MARINE MAMMAL
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The Davis Aerodrome Project (DAP) collected a range of environmental survey data over several field seasons to support a comprehensive environmental assessment of the proposed aerodrome. This data includes flora, fauna, soils, lake ecosystem, nearshore, marine, air quality and meteorological information which has been collected by a number of different methods, and extends across the current Davis Station, proposed aerodrome and supporting infrastructure footprint (Ridge Site), previous sites considered for the aerodrome (Heidemann Valley, Adams Flat), as well as locations across the Vestfold Hills away from any of the proposed developments. This dataset contains long-term underwater acoustic recordings made for the Australian Antarctic Division’s Davis Aerodrome Project 5097 environmental assessments. Calibrated measurements of sound pressure were made at two sites in the vicinity of Davis Research station (approx. 5km west of the station and one in Long Fjord to the north of station). The attached data was downloaded from the instrument deployed west of Davis Station. Data was recorded over 7 months using a custom moored Autonomous Multichannel Acoustic Recorder (AMAR G4) designed and manufactured by JASCO Applied Science following specifications provided by the Australian Antarctic Division. These moored acoustic recorders were designed to operate for year-long, near shore, Antarctic deployments. The moorings were deployed through the ice during the 2021 winter and one retrieved during the 2021/22 summer when the seaice was clear of the surface. The Autonomous Multichannel Acoustic Recorder is a fully autonomous underwater sound and data recorder. The acoustic recorder included a factory calibrated M36-100 hydrophone, data acquisition electronics and solid state digital storage (SDHC) to reduce power consumption and mechanical self-noise (e.g. from hard-drives with motors and rotating disks). Batteries, SDHC cards and electronics were placed in watertight pressure sealed PVC housing rated to a depth of 250 m. The moorings were secured to the seafloor by weights and suspended up into the water column by a string of floats attached to the top of the structure to separate the recorder and hydrophone from sea-bed. The hydrophone was securely mounted to the base of the AMAR housing. All connections between mooring components where taped with protective coverings to reduce mechanical self-noise from movement of the structure. The target noise floor of each recorder was below that expected for a quiet ocean at sea state zero. The data for each recording site comprise folders of 24-bit WAV audio files recorded on a duty cycle with two different sample rates. The duty cycle recorded for 60 s at a sample-rate of 512 kHz, followed immediately by a 580 s at a sample-rate of 32 kHz, and then 280 s off before repeating. The names of each WAV file correspond to instrument serial number followed by the start time (in UTC) of the file as determined by the AMAR’s real-time clock e.g. AMAR897.20210722T061621Z.wav would correspond to a wav from AMAR serial number 897 that starts at 06:16:21 on 22 July 2021 (UTC).
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Data Acquisition: DIFAR (DIrectional Fixing And Ranging) 53D sonobuoys were deployed every 30 minutes of longitude during each of the north-south sampling transects as part of the acoustic survey for marine mammals. Sonobuoys were also deployed opportunistically when large numbers of whales (in particular minke whales) were sighted. Additionally, on the initial E-W transect (#12) sonobouys were deployed prior to the majority of CTD stations. The VHF receiving system for the sonobuoys aboard the ship began with a 6 element YAGI antenna mounted atop the ship's mast. The sonobuoy's VHF signal output from the YAGI was amplified through an Advanced Receiver Research VHF amplifier and received on ICOM PCR-1000 VHF receivers modified to improve low frequency audio output. The audio signal passed through a low pass anti-alias filter (National Instruments analogue bessel SCXI module) and was recorded onto a laptop through a National Instruments E-series (model 6062E) sound card at a sampling rate of 48kHz. Difar sonobuoys have an effective audio response up to 2.5kHz before the low-pass filter roll-off starts. DIFAR bearing information is carried on 7.5 and 15kHz carrier frequencies. Once sonobuoys were deployed, recordings were made for at least 70 minutes unless the sonobuoy failed or the signal was lost. During recordings at CTD stations, recordings were typically made for the length of time it took to complete the CTD (4 or more hours). Data Processing: Signals were monitored in real-time during acquisition using Ishmael software (Dave Mellinger, http://www.bioacoustics.us/ishmael.html). A scrolling spectrogram (FFT size: 16384 samples, overlap: 50%, frequency range displayed: 0-1000 Hz, time scaling: 5 sec/cm) was monitored in real-time. Sounds of interest were clipped and the time and description were logged in the sonobuoy deployment data logs. Bearings to sounds were attained with a modified version of DiFarV (Mark McDonald, http://www.whaleacoustics.com ). Note that bearings to the ship noise given by DifarV are ~180 degrees off for an as yet undetermined reason (potentially deep cold water propagation effects), but the bearings to whale sounds and other sounds of interest are thought to be correct. This appears to be the case with a series of light bulb calibration tests I did, suggesting that bearings to other sounds are in fact, correct. After acquisition, recordings were also post-processed in Ishmael with two further passes, one examining 0-2.5kHz, and another monitoring 0-1kHz again, to ensure as many marine mammal sounds as possible were identified. Clips were also re-examined when necessary to ensure species were correctly identified. In instances when apparently multiple whales were calling, calculated bearings were used to determine whether the sounds came from different bearings, and hence, different whales. Dataset Format: The dataset description is in an excel workbook, with a summary sheet at the front. The summary sheet has a single line summarising each sonobuoy deployment. The sonobuoy deployment data log sheets are separated by days when the deployment began. Each is marked by date - eg 01.10 is the 10th of January. Each deployment has an initial entry and the following rows are a running log of the sonobuoy recording session. The data sheets and the summary sheet are in the following format with column headers from left to right: Observer(real time/post-processing)Summary of the sounds that occurred within the sample (70 minutes) Total recording length (in minutes) Date UTC time of deployment Initial latitude (decimal degrees) Initial Longitude (decimal degrees) Depth setting of sonobuoy hydrophone (90, 120, or 300m) National Instruments sound card gain (0, 5, or 10 times) Ship heading (true degrees) Ship speed (knots) Distance of deployment from CTD location (if applicable) UTC time of events (applies mainly to log of events in sonobuoy deployment data log) Species or sound description (applies mainly to sonobuoy deployment data log) Comments Sonobuoy type Raw data files are stored on a series of external hard drives. This work was completed as part of ASAC projects 2655 and 2679 (ASAC_2655, ASAC_2679).