Acoustic differentiation and classification of wild belugas and narwhals using echolocation clicks

Marie J Zahn,Jens C Koblitz,Marianne H Rasmussen,Shannon Rankin,Kristin L Laidre,Frederick Archer,Jennifer L Mccullough

doi:10.1121/10.0007585

Abstract

Belugas (Delphinapterus leucas) and narwhals (Monodon monoceros) are highly social toothed Arctic cetaceans with large vocal repertoires and similar acoustic profiles. Passive Acoustic Monitoring (PAM) that uses multiple hydrophones over large spatiotemporal scales has been the primary method to study their populations, particularly in response to rapid climate change and increasing underwater noise. This study marks the first acoustic comparison between wild belugas and narwhals from the same location and reveals that they can be acoustically differentiated and classified solely by echolocation clicks. Acoustic recordings were made in the pack ice of Baffin Bay, West Greenland during 2013. Multivariate analyses and Random Forests classification models were applied to eighty-one single-species acoustic events comprised of numerous echolocation clicks. Results demonstrate a significant difference between species’ acoustic parameters where beluga echolocation was distinguished by higher frequency content. Classification model predictive performance was strong with an overall correct classification rate of 97.5% for the best model. The most important predictors for species assignment were defined by peaks and notches in frequency spectra. Our results provide strong support for the use of echolocation in PAM efforts to differentiate belugas and narwhals.

Highlights

Belugas (Delphinapterus leucas) and narwhals (Monodon monoceros) are highly social Arctic toothed whales with large vocal repertoires and similar acoustic profiles
Passive Acoustic Monitoring (PAM) relies on the ability to distinguish between species solely based on their characteristic sounds, which means individual or a combination of specific sonic identifiers must be known for each species
Recordings were paired with visual confirmation of species, so all echolocation clicks were labeled as originating from belugas or narwhals

Summary

Introduction

Belugas (Delphinapterus leucas) and narwhals (Monodon monoceros) are highly social Arctic toothed whales with large vocal repertoires and similar acoustic profiles. Narwhals in the Canadian Arctic and West Greenland undergo extensive annual migrations with high site fidelity from their summer ranges in fjords of Greenland and Baffin Island to their wintering grounds in Baffin Bay and northern Davis S trait[3,13,15]. Across their respective distributions, belugas and most of the world’s narwhals overlap for much of the year in the waters of the Canadian Arctic and Baffin Bay, West Greenland, during their annual migrations (Fig. 1a). Acoustic classifiers may use a single call type or multiple call types to differentiate species[31]

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