In August 2023 and February 2024, Cascadia Research Collective (CRC) conducted small boat-based satellite tagging of odontocetes at the Pacific Missile Range Facility (PMRF), with acoustic support from Naval Information Warfare Center (NIWC) Pacific and Naval Undersea Warfare Center (NUWC) Newport, directing the tagging boat towards locations of acoustic detections on the range. Seventeen days of tagging effort were conducted over the two years during the biannual Submarine Command Course (SCC) training events. In total 19 odontocetes were tagged: 14 short-finned pilot whales (Globicephala macrorhynchus), 3 common bottlenose dolphins (Tursiops truncatus), 1 pantropical spotted dolphin (Stenella attenuata), and 1 melon-headed whale (Peponocephala electra). Additionally, 3 humpback whales (Megaptera noveangliae) were tagged in concert with this effort to test new tags, and that data was also analyzed herein.
The resulting tag tracks were smoothed and interpolated with positions every 5 mins using crawl in R, while dive profiles were modeled using a custom-built program in Matlab based on the output of the dive behavior log files. Received levels were estimated in 3D using a parabolic propagation modeling equation for every transmission from three sources producing mid-frequency active sonar (MFAS): hull-mounted MFAS from surface ships, active sonobuoys, and helicopter-dipping MFAS. The resulting received levels were binned by 5-mins, corresponding to the 5-min track positions, with the highest median received level (plus/minus 2 standard deviations) reported for each bin, along with an overall cumulative sound exposure level (cSEL) for each animal resulting from their total cumulated exposures.
Dive behavior was statistically analyzed across diel period (dawn, daytime, dusk, and nighttime) and SCC phase (Before, Phase A, Interphase, Phase B, After), when there was enough dive data across periods for analysis. Movement behavior in response to MFAS was assessed qualitatively. Resulting assessments indicated that there were some statistically significant differences in dive depth and dive duration for some individual pilot whales across different diel or SCC phases, but these differences varied by group or individual, with no consistent differences for any metric across any period. Dive rates and the percentage of time spent on the surface did not differ significantly for any individual across any period, and dive depths and durations did not differ significantly for any other species. No large scale or obvious horizontal movement was observed for any of the individuals, with several pilot whales and the melon-headed whale transiting back and forth across the range and relatively close to the areas of training activity throughout bouts of MFAS. However, the melon-headed whale did move off the range after their first, highest received level bout of exposures, which could have been a short distance, short duration avoidance behavior.
These results are discussed in the context of the residency status of individuals and species with all pilot whales being from resident, island-associated communities, and all three bottlenose dolphins also being from a resident, island-associated population. The melon-headed whale and spotted dolphin were not known individuals, but melon-headed whales have been increasingly observed in the Hawaiian Islands in the last eight years and therefore may be more frequently exposed to MFAS than they were a decade ago. These data will be added to the growing dataset of tagged odontocetes exposed to MFAS at PMRF. These aggregated data can be analyzed using more sophisticated modeling techniques to quantitatively assess behavior in response to MFAS, and to examine potential changes in response over time to look for changes in behavioral response patterns.
Citation:
Henderson, E.E., R.W. Baird, C. Martin, A.E. Harnish, M.A. Kratofil, S. Martin, C.J. Cornforth, and R.D. Andrews. 2025. Received Levels of Odontocetes Tagged During Submarine Command Courses at the Pacific Missile Range Facility in 2023 and 2024. Naval Information Warfare Center Pacific.
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