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Passive acoustics suggest two different feeding mechanisms in the Atlantic walrus (Odobenus rosmarus rosmarus)

Abstract

The vocal repertoire of walruses has been widely described in the bioacoustic literature. These marine mammals produce several distinct types of vocalizations for intraspecific communication during the breeding season. In this study, we provide the first evidence of walrus-generated sounds during foraging dives when they feed on bivalves. We recorded two types of sounds that we associated to different feeding mechanisms. The first sound type was brief and low in frequency that we relate to the suction of soft parts from the bivalves’ shells through the use of walrus powerful tongues, which is the common feeding behavior reported in the walrus literature. We also recorded a second sound type composed of multiple broadband pulse trains. We hypothesize the latter were associated with bivalve shell cracking by walruses, which would represent a new feeding mechanism in the walrus literature. This new feeding mechanism is either related to bivalves’ ecology or to walruses removing the sediment when searching for food. During this study, we observed bivalves lying on the seafloor instead of being buried in the sediment in walrus feeding areas while scuba diving. As a result, walruses cannot use suction to feed on soft body part of bivalves and have to use another strategy, mastication. Our findings provide a first step towards using passive acoustics to quantify walrus behavior and feeding ecology.

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Sound files may be requested by email to the corresponding author.

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MATLAB scripts may be requested by email to the corresponding author.

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Acknowledgements

We thank Xavier Mouy for his scientific expertise on walrus vocalizations. We would like to acknowledge the support of the MarineBasis program (part of the Greenland Ecosystem Monitoring) and Zackenberg staff during the surveys in Young Sound, especially Egon Frandsen and Henrik Spanggaard Munch. Special thanks to Jérôme Mars for his help in leading the GAAP project. We thank the Editor Piepenburg and four anonymous reviewers for their comments that greatly improved the manuscript. Funding was provided by the Institut Polaire Français Paul-Emile Victor (IPEV – PRIVARC project), CNRS Ec2co (Slecrarctic project), the European H2020 INTAROS program, the Agence Nationale de la Recherche (ANR GAAP). This study is an international collaboration between the BeBEST International Laboratory (UBO, UQAR, CNRS, and MNHN) and the Aarhus University.

Funding

Funding was provided by the Institut Polaire Français Paul-Emile Victor (IPEV – PRIVARC project), CNRS Ec2co (Slecrarctic project), the European H2020 INTAROS program, the Agence Nationale de la Recherche (ANR GAAP).

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Correspondence to Youenn Jézéquel.

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Jézéquel, Y., Mathias, D., Olivier, F. et al. Passive acoustics suggest two different feeding mechanisms in the Atlantic walrus (Odobenus rosmarus rosmarus). Polar Biol (2022). https://doi.org/10.1007/s00300-022-03055-y

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  • DOI: https://doi.org/10.1007/s00300-022-03055-y

Keywords

  • Bioacoustics
  • Bivalves
  • Feeding behavior
  • Marine mammal
  • Young Sound fjord