Samaran Flore

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Samaran
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Flore
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  • Article
    Broad-scale study of the seasonal and geographic occurrence of blue and fin whales in the Southern Indian Ocean
    (Inter-Research, 2018-12-13) Leroy, Emmanuelle C. ; Samaran, Flore ; Stafford, Kathleen M. ; Bonnel, Julien ; Royer, Jean-Yves
    The southern Indian Ocean is believed to be a natural territory for blue and fin whales. However, decades after commercial and illegal whaling decimated these populations, little is known about their current status, seasonal habitat or movements. Recent passive acoustic studies have described the presence of 4 acoustic populations of blue whales (Antarctic and 3 ‘pygmy’ types), but are generally limited temporally and geographically. Here, we examine up to 7 yr of continuous acoustic recordings (2010−2016) from a hydrophone network of 6 widely spaced sites in the southern Indian Ocean, looking for the presence of Antarctic and pygmy blue and fin whales. Power spectral density analyses of characteristic and distinct frequency bands of these species show seasonal and geographic differences among the different populations, and the overall patterns for each display interannual consistencies in timing and occurrence. Antarctic blue and fin whales are recorded across the hydrophone network, mainly from austral autumn to spring, with peak intensity in winter. Pygmy blue whales show spatial variation: Madagascan pygmy blue whales are mainly present in the west of the network, while the Australian call type is heard at the eastern sites. Both populations share a common seasonality, with a presence from January to June. Finally, the Sri Lankan call type is recorded only on a single site in the northeast. These results confirm the importance of the southern Indian Ocean for several populations of endangered large whales and present the first long-term assessment of fin whales in the southern Indian Ocean.
  • Article
    Long-term and seasonal changes of large whale call frequency in the Southern Indian Ocean
    (American Geophysical Union, 2018-11-27) Leroy, Emmanuelle C. ; Royer, Jean-Yves ; Bonnel, Julien ; Samaran, Flore
    In the past decades, in the context of a changing ocean submitted to an increasing human activity, a progressive decrease in the frequencies (pitch) of blue whale vocalizations has been observed worldwide. Its causes, of natural or anthropogenic nature, are still unclear. Based on 7 years of continuous acoustic recordings at widespread sites in the southern Indian Ocean, we show that this observation stands for five populations of large whales. The frequency of selected units of vocalizations of fin, Antarctic, and pygmy blue whales has steadily decreased at a rate of a few tenths of hertz per year since 2002. In addition to this interannual frequency decrease, blue whale vocalizations display seasonal frequency shifts. We show that these intra‐annual shifts correlate with seasonal changes in the ambient noise near their call frequency. This ambient noise level, in turn, shows a strong correlation with the seasonal presence of icebergs, which are one of the main sources of oceanic noise in the Southern Hemisphere. Although cause‐and‐effect relationships are difficult to ascertain, wide‐ranging changes in the acoustic environment seem to have a strong impact on the vocal behavior of large baleen whales. Seasonal frequency shifts may be due to short‐term changes in the ambient noise, and the interannual frequency decline to long‐term changes in the acoustic properties of the ocean and/or in postwhaling changes in whale abundances.