Localization of Beaked Whales Offshore Guam

These results were presented at the International Bioacoustics Congress (IBAC) 2023.

This collaborative project aimed to characterize Cuvier’s beaked whale (Ziphius cavirostris) abundance with a hydrophone array deployed offshore Guam. Beaked whales, a family of cetaceans comprising about two dozen species, are seldom seen due to their elusive deep-diving behavior. Historically, beaked whale strandings were rare; however, stranding rates have increased greatly since the 1960s, with over a hundred mass stranding events reported between 1960 and 2004. Furthermore, such events have repeatedly coincided with nearby naval exercises — specifically, with the use of mid-frequency active sonar (MFAS) — raising concern about the damaging impact of sonar on beaked whales and underscoring the need for ecologically-informed protective measures. While beaked whales are difficult to observe visually, they emit echolocation clicks during foraging, enabling the use of acoustics as a proxy for presence.

From June to November of 2022, five Rockhopper hydrophones recorded continuously offshore western Guam, the site of a major base of the US Navy. Using PAMGUARD, our collaborators automatically detected and classified echolocation clicks for Cuvier’s beaked whale over the six-month deployment. Using pingers associated with each unit, I quantified clock drift, measured empirical travel times, and synchronized the five channels for intervals containing beaked whale detections. Next, I implemented time-difference-of-arrival-based likelihood-surface localization, obtained a relative spatial distribution of beaked whale activity, and calculated a detection function for use in distance sampling.