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ORIGINAL RESEARCH article

Front. Mar. Sci.
Sec. Marine Megafauna
Volume 11 - 2024 | doi: 10.3389/fmars.2024.1378524
This article is part of the Research Topic The ACCOBAMS Survey Initiative (ASI): Implementing Large Scale Surveys for Marine Megafauna in the Mediterranean and Black Seas View all 12 articles

Temporal patterns in dolphin foraging activity in the Mediterranean Sea: insights from vocalisations recorded during the ACCOBAMS Survey Initiative

Provisionally accepted
Morgane Sol Morgane Sol 1*Camille Ollier Camille Ollier 1,2Oliver Boisseau Oliver Boisseau 3Vincent Ridoux Vincent Ridoux 1,2Auriane Virgili Auriane Virgili 4
  • 1 UAR 3462 Observatoire Pelagis, La Rochelle Université/CNRS, La Rochelle, France
  • 2 UMR7372 Centre d'études biologiques de Chizé (CEBC), Villiers En Bois, Poitou-Charentes, France
  • 3 Marine Conservation Research International, Kelvedon, United Kingdom
  • 4 Share the Ocean, Larmor Baden, France

The final, formatted version of the article will be published soon.

    Marine organisms continually adapt their physiology and behaviour to temporal variations in their environment, resulting in diurnal rhythmic behaviour, particularly when foraging. In delphinids, these rhythms can be studied by recording echolocation clicks, which can provide indicators of foraging activity. The foraging rhythms of delphinids and their relationship to environmental parameters are poorly documented and most studies so far have used moored passive acoustic systems. The present study provides, for the first time, information on the activity rhythms of delphinids investigated in relation with temporal variables at a basin scale from a moving platform, in the western and central Mediterranean Sea. We used passive acoustic recordings collected by hydrophones towed along transect lines during the ACCOBAMS Survey Initiative in the summer 2018. We extracted variables that may influence daily and monthly rhythms, including time of day, lunar cycle, lunar illumination and sea state and fitted generalised additive models. The nycthemeral and lunar cycles were the two main factors influencing dolphin activity rhythms. Echolocation activity was predominant at night, with a maximum of 0.026 acoustic events per minute at 21:00/22:00 compared to as few as 0.0007 events per minute at 11:00. These events were also more frequent during the third quarter of the moon; 0.033 acoustic events on day 22 of the lunar cycle as opposed to 0.0008 on day 8 of the lunar cycle, corresponding to the first quarter of the moon. Variations in the echolocation activity of delphinids in the Mediterranean Sea could reflect variation in their foraging effort and be related to prey density, composition, accessibility and catchability within dolphin foraging depth range. These results should also improve interpretation of passive acoustic monitoring data.

    Keywords: foraging activity rhythms, Generalised Additive Models (GAMs), Delphinids, Echolocation clicks, Mediterranean Sea

    Received: 29 Jan 2024; Accepted: 11 Jul 2024.

    Copyright: © 2024 Sol, Ollier, Boisseau, Ridoux and Virgili. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Morgane Sol, UAR 3462 Observatoire Pelagis, La Rochelle Université/CNRS, La Rochelle, France

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