An unknown nocturnal call type in the Mariana Archipelago

Area of Science:

• Marine bioacoustics
• Cetacean research
• Oceanography

Background:

• Marine mammal vocalizations are crucial for understanding species behavior and distribution.
• Previous acoustic surveys in the Mariana Archipelago have not identified this specific sound signature.

Purpose of the Study:

• To identify the source of a previously undocumented, low-frequency tonal call detected in the Mariana Archipelago.
• To investigate the spatiotemporal distribution and characteristics of this novel acoustic signal.

Main Methods:

• Deployment of drifting acoustic recorders in the U.S. Exclusive Economic Zones of the Mariana Archipelago during 2018 and 2021.
• Manual analysis of acoustic data to characterize call parameters (frequency, duration, temporal patterns).
• Comparison of the detected call with known vocalizations of marine fauna.

Main Results:

• A stereotypic, low-frequency (median 473-554 Hz), short-duration (median 0.596 s), tonal nocturnal call was consistently detected across the Mariana Archipelago.
• The call exhibited distinct temporal patterns and was not associated with chorusing behavior.
• The call's characteristics and co-occurrence with Bryde's whale calls suggest a potential source.

Conclusions:

• The detected 500-Hz pulsed call is hypothesized to be produced by Bryde's whales (Balaenoptera brydei).
• This finding contributes to the understanding of Bryde's whale acoustic behavior and distribution in the Pacific Islands region.
• Further research is recommended to confirm the source of this unique marine sound.