ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01377

ABSTRACT: We presently have an incomplete understanding of hearing in Hawaiian monk seals Neomonachus schauinslandi. Their auditory biology is important from a conservation perspective and is especially intriguing given their long evolutionary isolation from related seal species. Available audiometric data for 2 individuals are conflicting but suggest that monk seals have limited aquatic and terrestrial hearing abilities compared to the more well-studied species in the Phocinae subfamily of seals. To resolve representative amphibious hearing profiles for Hawaiian monk seals, we describe auditory sensitivity for 1 additional seal trained to participate in a psychophysical task while submerged and on land. Detection thresholds were measured for narrowband signals across the frequency range of hearing under water and at select frequencies in air. This individual demonstrated poor sensitivity in both media, with notable insensitivity to high-frequency waterborne sounds and an overall decreased ability to detect airborne sounds. The range of functional hearing was wider in water (<0.1–40 kHz) than in air (0.1–33 kHz), with peak sensitivities of 73 dB re 1 µPa (at 18 kHz) and 42 dB re 20 µPa (at 3.2 kHz), respectively. These data confirm recently published behavioral audiograms as typical for the species. When considered with the limited available data for related species, these findings suggest that hearing within the Monachinae subfamily of seals differs from that of the highly sensitive Phocinae seals. This study advances knowledge of the evolution of hearing in amphibious marine mammals and supports conservation and management decisions for the endangered Hawaiian monk seal.