Source levels of Western Australian Omura's whale (Balaenoptera omurai) sound

The Omura's whale (Balaenoptera omurai), a species inhabiting the tropical waters off of Western Australia, was identified as a new species in 2003 and has been classified as "data deficient" to date. One way of studying whale species is passive acoustic monitoring (PAM). At least one type of Omura's whale vocalization has been attributed to this species by simultaneous visual and acoustic observations. Although the spectral features of Omura's whale sound have been described, the source level (SL) remains undetermined. Knowledge of the SLs of acoustic vocalizations by whales is needed to estimate detection ranges for PAM to better understand whale acoustic behavior and assess the effects of surrounding noise. In this study, the SL of Omura's whale sound was estimated from passive acoustic recordings produced with four autonomous recorders deployed in a tracking array configuration. Acoustic detections were used to localize individual whales and estimate the source sound level after correction for propagation loss. A total of 29 calls were localized, resulting in the estimated mean SL of Omura's whale sound varying from about 180 dB to nearly 190 dB re 1 μPa m.