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Quantifying the Behavior of Humpback Whales (Megaptera novaeangliae) and Potential Responses to Sonar
Abstract: Thirteen humpback whales (Megaptera novaeangliae) were tagged with LIMPET-configured SPLASH tags off Kaua‘i, Hawai‘i, near the Pacific Missile Range Facility (PMRF) in 2017 and 2018. The movement and dive behavior of the seven animals tagged in 2017 provided a baseline against which to compare the data from five of the six tagged whales in 2018 that remained in proximity of an active Navy training event occurring on PMRF. Although some extreme travel speeds (up to 18 km/h) were estimated for the whales in 2018, they did not co-occur with periods of mid-frequency active sonar (MFAS) and, in fact, travel speeds were reduced in two animals during periods of MFAS. The tagging effort took place at different points in the breeding season across years and in slightly different locations (offshore vs nearshore) and, therefore, some of the behavioral differences could have been due to targeting different sectors of the breeding population. One animal did have significant changes to their dive behavior during one period of sonar, with steep, deep dives occurring while the animal moved away from the location of the sonar activity and received levels up to 158 dB re 1 µPa. Thus, some behavioral response may have occurred in the presence of MFAS, but this appears to have been relatively limited, with the whales likely focused on breeding behavior. Further monitoring is necessary to address these confounding factors and to ensure that any temporary behavioral responses do not have long-term consequences to the population.
Key Words: humpback whales, Megaptera novaeangliae, satellite tagging, sonar, behavioral response
Page Numbers: 612-631