A Whale With No Name: Search for an unknown long-duration beaked whale (Cetacea; Ziphiidae) signal across ocean basins

Abstract

Beaked whales (Cetacea: Ziphiidae) are known for producing frequency-modulated (FM) echolocation signals that are characteristic of each species, yet several species still lack confirmed FM signal descriptions. A distinctive FM signal, long in duration, and occurring only at night, has previously been documented in the North Pacific, the western Gulf of Mexico, and the Gulf of Guinea, but its broader distribution has not been assessed. Here, carried out is a basin-wide analysis of numerous passive acoustic monitoring projects to identify additional regions where this signal is present. Our dataset comprised 19 monitoring efforts (156 total datasets) spanning latitudes from 72° N to 42° S. An automated detector-classifier (per file Precision = 1.00 and Recall = 1.00) was run on all audiofiles to identify possible detections, which were subsequently reviewed and confirmed manually. We report the presence of this FM signal in five previously unrecognized areas: along a glider transect (512 kHz) near the Canary Islands; on three bottom-mounted recorders (250–512 kHz) off Western Australia; and from a single detection on Blake’s Plateau in the southeastern United States. Across all monitoring sites, detections occurred only during local nighttime hours and were not observed at latitudes higher than 29° N or 19° S. The signal’s median centre and peak frequencies ranged from 51 to 67 kHz, its median duration from 500 to 630 μs, and its −10 dB bandwidth from 19 to 28 kHz. This FM signal remains the longest known among both identified and unidentified beaked whale FM signal types. Although the producing species has yet to be determined, the signal’s temporal and spectral features were remarkably consistent across ocean basins. These results extend the known distribution of this unique FM signal and highlight the value of broad, cross-regional acoustic collaborations in uncovering previously unrecognized regions of beaked whale vocal behaviour and biogeography.