Marine geophysical surveys use high-powered acoustic sources to image subsurface features. Traditional compressed airgun sources produce intense impulsive broadband noise, though only frequencies below ~200 Hz are of practical use. Given demand for reduced-impact alternative imaging sources, offshore energy industry partners launched efforts to operationalize marine vibrators (MV) that concentrate output energy at these low frequencies and have lower rise time and peak pressures. These parameters likely reduce or eliminate potential impacts on marine species that hear and/or utilize higher frequencies. However, key questions remain for species that make and rely on low frequency sounds, notably large baleen whales. We conducted controlled exposure experiments to obtain novel baseline behavior and behavioral response data for ESA-listed, very low frequency whales to a full-scale operational MV source in realistic field conditions. The study occurred in the Southern California Bight and focused on blue (Balaenoptera musculus) and fin (Balaenoptera physalus) whales. A strategic multi-scale tagging approach utilized both longer duration (weeks) dart-attached depth and movement sensing and shorterterm (days) suction-cup attached high-resolution depth, movement, and acoustic tags. Tag data was augmented with passive acoustic monitoring of MV exposure and calling behavior, individual focal follows, photo identification, and body condition measurements made from uncrewed aerial systems. The MV source was an operational, full-scale prototype that produced repeated signals during 30-minute exposure periods with the following source parameters: 5–100 Hz linear FM sweeps, 5-second signal duration, 50% duty cycle, and up to 190 dB re: 1μPa RMS sound pressure level across the band. Two pilot studies using lower power sound sources simulating operational MV signals were conducted in 2022 and 2023. During the primary effort in 2024 with the operational MV source, a total of 33 tags were deployed (32 blue whales and 1 fin whale), yielding nearly 2500 hours of behavioral data. Eight 90-minute experiments (30-min phases before, during, post-exposure) were conducted (six with operational MV signals and two no-noise “control”). Results from pilot studies with simulated MV playbacks indicated mild and temporary avoidance responses by blue whales that were either traveling or feeding in areas of lower prey density. Field observations and initial analyses of the tests with the operational MV source, however, did not indicate broadscale avoidances or strong changes for whales feeding intensely in locations of concentrated prey.
Citation:
Southall, B.L., J. Fahlbusch, C. Casey, S. Fregosi, H. Clayton, J. Barkowski, R. Jones, & J. Calambokidis. 2026. A Behavioral Response Study with an Operational Marine Vibrator and Very Low Frequency Whales. Pages 1-13 in The Effects of Noise on Aquatic Life IV. Edited by A.N. Popper. Springer Nature. doi: 10.1007/978-3-031-94229-7_131-1
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