Dive characteristics of Cross Seamount beaked whales from long-term passive acoustic monitoring at the Pacific Missile Range Facility, Kaua'i

Beaked whale foraging pulses were detected on the Pacific Missile Range Facility (PMRF) off Kaua'i, Hawaii, via long term passive acoustic monitoring. The unidentified pulses do not match foraging pulses of known species on the range but are similar to the unidentified beaked whale first detected at Cross Seamount, Hawaii. Although there has not been a visual confirmation of the unidentified beaked whale species, analysis of data collected from 2007 to 2019 has identified beaked whale foraging dive characteristics from echolocation pulses. From the 13 years of data, the most distinct patterns were that all foraging dives occurred at night and the nighttime foraging dive rate was Oil group vocal periods (GVP) per hour, with most detections on shallow hydrophones (625-1,000 m deep) over steep bathymetric slopes. Data collected during U.S. Navy training events were used to compare dive behavior during midfrequency active sonar (MFAS) activity against baseline periods; it was determined that the whales reduced GVPs during sonar and these remained low for at least 3 days after the training events. These results are the first longterm record of acoustic signals from the Cross Seamount beaked whale and provide important insights into their habitat use and occurrence patterns.

Automated summary

Long-term passive acoustic monitoring detected beaked whale foraging pulses off Kaua'i, Hawaii. The species of these unidentified pulses is still unknown, but their foraging dive characteristics were identified through data analysis. The study also found that the whales reduced their vocalizations during sonar activity.