Humpback whale: Yes/no? Challenges with passive acoustic monitoring of this well-described species

Abstract

Humpback whales sing song and produce non-song sounds. Dozens of research articles have described their acoustic repertoire—even if only considering Australian waters. While song structure changes slowly over seasons, individual notes may exhibit multi-decadal stability. Irrespectively, automatically detecting humpback whale vocalizations remains an ongoing development activity while manual validation of automated detections continues to be problematic. While analysing archival recordings from Australian waters using the NOAA/Google convolutional neural network pretrained for humpback whale song [https://tfhub.dev/google/humpbackwhale/1], we found numerous instances of a particular type of sound with spectrographic features resembling those of humpback whale vocalizations. These sounds lacked the context of a song and occurred in chorus-like patterns, withthe same sound recorded at varying received levels and overlapping in time—indicative of many animals simultaneously producing nothing but this specific call. To investigate these phenomena further, we (1) built a custom detector for these specific calls, (2) ran the detector on archival recordings from North-western Australia, and (3) compared geographic and seasonal presences and absences to known patterns of humpback whale occurrence. The likelihood of these scenarios being humpback whales is discussed.