Auditory biology of bearded seals ( Erignathus barbatus )
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ORIGINAL PAPER
Auditory biology of bearded seals (Erignathus barbatus) Jillian M. Sills1 · Colleen Reichmuth1,2 · Brandon L. Southall1,3 · Alex Whiting4 · John Goodwin4 Received: 8 November 2019 / Revised: 13 August 2020 / Accepted: 18 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Bearded seals (Erignathus barbatus) have a circumpolar Arctic distribution and are closely associated with unstable pack ice, spending nearly all of their lives in remote habitats. As a result, their biology and behavior remain largely unknown. With respect to sensory biology, bearded seals—like other marine mammals—rely on acoustic cues to support a range of vital behaviors. Acoustic monitoring from moored instrumentation has revealed a rich repertoire of underwater calls associated with the breeding season. However, the ability of bearded seals to perceive sound has never been investigated. In this study, species-typical auditory profiles were obtained from two young male bearded seals trained to cooperate in a go/no-go sound detection paradigm. Hearing thresholds were measured for underwater tonal sounds at frequencies between 0.1 and 61 kHz, in quiet conditions and in the presence of octave-band masking noise. The bearded seals displayed sensitive underwater hearing with peak sensitivity near 50 dB re 1 µPa and a broad frequency range of best hearing extending from approximately 0.3 to 45 kHz. Additionally, the two seals performed particularly well compared to other mammals when detecting target signals embedded within background noise; critical ratios ranged from 12 to 30 dB between 0.1 and 25.6 kHz. These findings improve understanding of the acoustic ecology of bearded seals, inform best management practices related to anthropogenic noise in Arctic habitats, and provide insight into comparative auditory capabilities within the lineage of phocid seals. Keywords Bearded seal · Acoustic ecology · Audiogram · Hearing · Arctic · Noise
Introduction True seals (family Phocidae) are amphibious carnivores comprising 18 extant species. Within the Phocidae lineage, the Phocinae subfamily includes 10 species inhabiting the North Pacific, North Atlantic, and circumpolar seas of the northern hemisphere, as well as some freshwater regions. The largest of these ‘northern’ phocids is the bearded seal (Erignathus barbatus, Erxleben 1777), which—as the earliest diverging lineage in the Phocinae subfamily—is sister Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00300-020-02736-w) contains supplementary material, which is available to authorized users. * Jillian M. Sills [email protected] 1
Long Marine Laboratory, Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, CA, USA
2
Alaska SeaLife Center, Seward, AK, USA
3
SEA, Inc., Aptos, CA, USA
4
Native Village of Kotzebue, Kotzebue, AK, USA
to the remaining nine northern seals and is separated from these related species by 11 to 17 million years (Árnason et al. 2006;
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