Minke whales (Balaenoptera acutorostrata) respond to navy training

Minke whales (Balaenoptera acutorostrata) were acoustically detected and localized via their boing calls using 766 h of recorded data from 24 hydrophones at the U.S. Navy's Pacific Missile Range Facility located off Kauai, Hawaii. Data were collected before, during, and after naval undersea warfare training events, which occurred in February over three consecutive years (2011–2013). Data collection in the during periods were further categorized as phase A and phase B with the latter being the only period with naval surface ship activities (e.g., frigate and destroyer maneuvers including the use of mid-frequency active sonar). Minimum minke whale densities were estimated for all data periods based upon the numbers of whales acoustically localized within the 3780 km² study area. The 2011 minimum densities in the study area were: 3.64 whales [confidence interval (CI) 3.31–4.01] before the training activity, 2.81 whales (CI 2.31–3.42) for phase A, 0.69 whales (CI 0.27–1.8) for phase B and 4.44 whales (CI 4.04–4.88) after. The minimum densities for the phase B periods were highly statistically significantly lower (p < 0.001) from all other periods within each year, suggesting a clear response to the phase B training. The phase A period results were mixed when compared to other non-training periods.