Hearing in the Australian sea lion ( Neophoca cinerea ): First audiogram predictions from CT-based finite element analysis

Anthropogenic noise from seismic surveys, offshore wind, and shipping poses a growing threat to pinnipeds, including the Endangered Australian sea lion (Neophoca cinerea). Despite their vulnerability, little is known about their auditory capabilities due to the challenges of conducting direct hearing measurements. Understanding their hearing sensitivity is essential for assessing the risks associated with increasing ocean noise across their habitat. In this study, specimens from different age groups were collected to build computed tomography (CT) imaging-based finite element models of sound reception. These models were used to predict in-air and underwater audiograms for Australian sea lions across a broad frequency range (100 Hz–20 kHz in air and 100 Hz–40 kHz underwater), providing the first quantitative estimates of their auditory sensitivity. The predicted audiograms closely align with those of the California sea lion (Zalophus californianus), suggesting that California sea lion hearing data may serve as a reference for environmental impact assessments. This work demonstrates a promising approach for investigating hearing in other inaccessible marine mammals. Beyond Australian sea lions, this method establishes a novel framework for predicting auditory sensitivity in species where direct hearing assessments are not feasible. The results provide critical data for assessing noise impacts, informing mitigation strategies, and enhancing conservation efforts for pinnipeds and other marine mammals.