Acoustic presence data on Antarctic blue whales (Balaenoptera musculus intermedia) were obtained from passive acoustic monitoring (PAM) data collected at five different positions in the Weddell Sea and along the Greenwich meridian between March 2008 and November 2013. Passive acoustic recorders used were of type Sono.Vault (manufactured by develogic GmbH, Hamburg, Germany) or type AURAL (Autonomous Underwater Recorder for Acoustic Listening (AURAL; Model 2, Multi-Électronique). The acoustic recorders were attached to oceanographic deep-sea moorings of the Hybrid Antarctic Float Observation System (HAFOS) and a total of 10 acoustic recorders was deployed during three consecutive periods of recorder deployment: March 2008-December 2010; December 2010-December 2012; and December 2012-December 2014. Recorders were moored at depths between ca. 200 m and 1000 m. Sono.Vault recorders were scheduled to record continuously at sample rates of 5,333 Hz. AURAL recorders were scheduled to record on duty cycles of 4.5 min per 3 hours or 5 min per 4 hours at sample rates of 32.768 Hz. After recovery, the passive acoustic data were prepared for further analysis following the Standard Operating Procedures (SOP) for PAM data collected by the Ocean Acoustics Group of AWI according to Thomisch et al. (2023a, regarding definitions and terminology) and Thomisch et al. (2023b, with regard to data preparation procedures).
Daily acoustic presence of Antarctic blue whales was assessed based on automated detections of Z-call vocalizations by spectrogram cross-correlation using a pre-defined spectrogram template in a frequency band from 17.5 to 29 Hz. Received levels were obtained for each detected Z-call, as sound pressure level SPLrms [dB re: 1μPa] within the 25–29 Hz band of each detected Z-call event, for details on automated detection please refer to Thomisch et al. (2016). To avoid a spatial mismatch between the actual position of calling animals and the recorders, ABW detections were filtered to only keep detections that originated from within a ~10 km radius from the recorders. Assuming a source level of 189 dB re: 1μPa over 25–29 Hz and a spherical transmission loss TL[dB] = 20log₁₀(r), approximate distances between vocalizing Antarctic blue whales and the respective recording site locations were estimated for each detected Z-call. Daily acoustic presences were estimated as days with at least one detection event within a ~10 km radius of the respective recording sites; i.e., Z-calls with calculated received levels of ≥109 dB, considering a nominal TL of 80 dB. Data presented in this current publication series were used together in presence-only species distribution models (SDMs) to predict the year-round habitat suitability of Antarctic blue whales in the Weddell Sea (El-Gabbas et al. 2023). Data contain information on the detection time and the estimated received level SPLrms [dB re: 1μPa] for each Antarctic blue whale vocalization within a ~10 km radius from the respective recorders.
