Dear MARMAM community,

We are pleased to announce the publication of our new article entitled “BW90: The Highest Frequency Clicks Ever Recorded for a Beaked Whale.”

The article is open access at the following link:
https://onlinelibrary.wiley.com/doi/10.1111/mms.70161

Rodrigues-Soares, N., R. B. Machado, Y. Viana, and A. Andriolo. 2026. “BW90: The Highest Frequency Clicks Ever Recorded for a Beaked Whale.” Marine Mammal Science 42(2): e70161. https://doi.org/10.1111/mms.70161.

Abstract:
Beaked whales are deep-diving odontocetes with cryptic behavior, which makes their detection through visual surveys challenging. Passive Acoustic Monitoring (PAM) is essential for studying this group, as many species emit species-specific frequency-modulated (FM) pulses that enable acoustic discrimination. In the Southwest Atlantic Ocean (SWAO), knowledge of beaked whale diversity and acoustic repertoires remains limited. In this study, we describe a new type of FM pulse attributed to a beaked whale, recorded during two passive acoustic monitoring surveys conducted in deep offshore waters off northeastern Brazil in 2020 and 2025. Recordings were obtained using a 300 m linear array composed of four omnidirectional hydrophones (sensitivity of −205 dB re 1 V/µPa) operating at a sampling rate of 500 kHz, and were analyzed using PAMGuard and Raven software, as well as custom routines developed in R and Python. A total of 378 FM pulses were detected (313 in 2020 and 65 in 2025), along with a small number of non-modulated echolocation clicks recorded during the first detection. Principal Component Analysis (PCA) revealed substantial overlap among detections, suggesting a single acoustic signal type, designated BW90. The FM pulses exhibited peak frequencies around 90 kHz, higher than those reported for any known beaked whale species, and showed distinct temporal and spectral characteristics. Using published data, we examined the relationship between peak frequency and body length across beaked whale species and found a strong inverse relationship (R² = 0.79; p < 0.001), suggesting that the species producing BW90 is likely small-bodied, with an estimated body length of approximately 3.2 m—smaller than any described beaked whale species.These results indicate that BW90 may be associated with a beaked whale species that has not yet been acoustically classified or formally described, highlighting PAM as a powerful tool for detecting cryptic biodiversity in poorly studied oceanic regions.

Best regards,
Raphael Machado