DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Effects of Noise and Tonal Stimuli on Hearing in Pinnipeds

Pinnipeds (seals, sea lions, and walruses) are amphibious carnivores that are particularly susceptible to coastal anthropogenic noise impacts. The long-term goals of this effort are to improve understanding of 1) the sound detection capabilities of pinnipeds, and 2) the auditory effects of noise exposure on pinnipeds. OBJECTIVES In order to examine sound detection capabilities, well established psychoacoustic methods are applied with captive, trained animals in a laboratory setting, and electrophysiological methods are developed, applied, and optimized with anesthetized animals in a rehabilitation setting. These complementary approaches are used to obtain accurate measurements of hearing sensitivity as a function of sound amplitude, sound frequency, and, when possible, transmission medium (air or water), with the aim of establishing reasonable estimates of within- and between-subject variability in auditory performance. In order to examine the residual auditory effects of noise exposure on pinnipeds, carefully controlled laboratory experiments are conducted with highly trained animals. Hearing sensitivity is evaluated prior to and following exposure to broadband or tonal noise, and hearing thresholds are repeatedly measured over time. The specific goals of this effort are to model the onset, growth, and recovery of noise-induced temporary threshold shift (TTS) with respect to the duration, amplitude, and energy of the noise exposure; to opportunistically explore the relationship between temporary and permanent auditory threshold shifts; and to determine how hearing thresholds change permanently as a function of aging