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Long-term acoustic monitoring of nonstereotyped blue whale calls in the southern Indian Ocean
Monitoring the presence of blue whale (Balaenoptera musculus ssp.) stereotyped calls has been a widely used method to assess the different populations' distribution worldwide. All blue whale populations also produce nonstereotyped vocalizations, or D-calls. Here, we monitored the presence of D-calls in long-term records from a large hydrophone array located in the open southern Indian Ocean, using an automated detection method and manual validation of the detections. D-calls were detected at all sites of the array, which extends from 24°S to 56°S, but the majority of them were detected at the two southernmost sites. We observed a latitudinal shift in their seasonal occurrence, with more D-calls in the north during austral autumn and winter and more in the south during austral spring. The geographical occurrence of D-calls compared to that of songs indicates that blue whale acoustic behavior switches from a song-intensive and sparse-D-call emission in the north to song-moderate and more intensive D-call emissions in the south. These findings support the hypothesis that both call types are used for different purposes, as D-calls are mainly detected around foraging grounds and songs in wintering grounds. Monitoring both call types might therefore be a relevant acoustic indicator of blue whale behavior.
Keyword(s)
Antarctic blue whale, Balaenoptera musculus, D-calls, passive acoustic monitoring, pygmy blue whale, southern Indian Ocean
Full Text
File | Pages | Size | Access | |
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Publisher's official version | 17 | 7 Mo | ||
FIGURE S1: Weekly proportion of files with airgun signals for every year of recording. Black crosses indicate weeks with no available recordings. | 1 | 602 Ko | ||
FIGURE S2: Weekly number of D-calls detected, normalized by the corrected week duration. Black crosses indicate weeks with no available recordings. Season are color coded as follow: summer: green; ... | 1 | 1 Mo | ||
Author's final draft | 33 | 2 Mo |