We Go Signaling Into the Night: Describing an Echolocation Signal of an Unknown Beaked Whale (Cetacea; Ziphiidae) off West Africa

Abstract

Beaked whales (Cetacea; Ziphiidae), one of the most diverse families of cetaceans, can be identified by species-specific, frequency-modulated echolocation signals. Of the 24 known species of beaked whales, over half have been assigned a unique signal type. A novel echolocation pulse belonging to an unknown beaked whale species was recorded off West Africa (Beaked Whale of West Africa, BWWA), along the coast of the Democratic Republic of São Tomé and Príncipe. Bottom-mounted autonomous acoustic recorders (sampling rate of 375 kHz) were deployed from October 2018 to August 2019 (294 recording days) at depths of 450–600 m. An automated detector-classifier created to identify BWWA (per file Precision of 1.00; Recall of 1.00)-guided manual validation. BWWA was present in all recording months and detected during local nighttime hours (98% of detections occurred during fully dark periods). BWWA had a 52.5 kHz median peak frequency, 55.4 kHz center frequency, 29.0 kHz −10 dB bandwidth, 843 μs duration, and 86 ms inter-pulse interval (IPI). While species identification remains unsolved for BWWA, spectral similarities to unidentified signals in the Pacific Ocean, BWC, and in the Gulf of Mexico, BWG, find that all three signals can be characterized by longer pulse durations and shorter IPIs.