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Trumpet sounds emitted by male sperm whales in the Mediterranean Sea.

ABSTRACT: Sperm whale trumpets are sounds only occasionally documented, with a well recognisable and stereotyped acoustic arrangement. This study investigated the acoustic features of the trumpets and the context in which these sounds were recorded, using acoustic data collected over 22 years, in the Pelagos Sanctuary area (North-Western Mediterranean Sea). Analysed trumpets (n?=?230), recorded at the beginning of a dive after the whale fluke-up, comprised a series of acoustic units organized in short sequences. Acoustic parameters were derived for the entire trumpet and for each distinguishable unit in a trumpet. Overall, trumpet durations and their initial frequencies were higher in recordings collected when multiple whales were visually or acoustically detected in the observation area. The identity of 68 whales was assessed through photo-identification, with 29 individuals producing trumpets within and between years. The variability of the acoustic parameters appeared to be higher within the same individuals rather than between different individuals, suggesting an individual plasticity in composing and arranging units in a trumpet. Different click patterns were observed before and after the trumpets, with more complex sequences when (1) other whales were visually/acoustically detected, and (2) individuals were in suitable foraging sites (i.e., canyon areas). Trumpets were commonly followed or preceded by click patterns suited for communication, such as codas and/or slow clicks. Significant relations between the trumpet emission and the male-only long-range communication click pattern (i.e. slow clicks) emerged, supporting the hypothesis that a trumpet is a sound emitted by maturing/mature males in feeding grounds. This study provides the first evidence that trumpets were conserved in the sperm whale acoustic repertoire at the decadal timescale, persisting across years and individuals in the same area. This persistence may be functionally specific to foraging activities performed by males in a well-established feeding area.

SUBMITTER: Pace DS

PROVIDER: S-EPMC7955081 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe Mediterranean subpopulation of fin whale Balaenoptera physalus (Linnaeus, 1758) has recently been listed as Vulnerable by the IUCN Red List of threatened species. The species is also listed as species in need of strict protection under the Habitat Directive and is one of the indicators for the assessment of Good Environmental Status under the MSFD. Reference values on population abundance and trends are needed in order to set the threshold values and to assess the conservation status of the population.MethodsYearly summer monitoring using ferries as platform of opportunity was performed since 2008 within the framework of the FLT Med Network. Data were collected along several fixed transects crossing the Western Mediterranean basin and the Adriatic and Ionian region. Species presence, expressed by density recorded along the sampled transects, was inspected for assessing interannual variability together with group size. Generalized Additive Models were used to describe density trends over a 11 years' period (2008-2018). A spatial multi-scale approach was used to highlight intra-basin differences in species presence and distribution during the years.ResultsSummer presence of fin whales in the western Mediterranean area showed a strong interannual variability, characterized by the alternance of rich and poor years. Small and large groups of fin whales were sighted only during rich years, confirming the favorable feeding condition influencing species presence. Trends highlighted by the GAM can be summarized as positive from 2008 to 2013, and slightly negative from 2014 to 2018. The sub-areas analysis showed a similar pattern, but with a more stable trend during the second period in the Pelagos Sanctuary sub-area, and a negative one in the other two sub-areas. Our findings further confirm the need for an integrated approach foreseeing both, large scale surveys and yearly monitoring at different spatial scales to correct and interpret the basin wide abundance estimates, and to correlate spatial and temporal trends with the ecological and anthropogenic drivers.

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Trumpet sounds emitted by male sperm whales in the Mediterranean Sea.

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