Pinniped Hearing in Complex Acoustic Environments

Abstract

Award Number: N000140610295 http://pinnipedlab.ucsc.edu LONG-TERM GOALSPinnipeds (seals, sea lions, and walruses) are amphibious marine mammals that are susceptible to coastal anthropogenic noise. The long-term goals of this effort are to improve understanding of (1) the sound detection capabilities of several pinniped species, and (2) the effects of noise exposure on the sound detection capabilities of these species. The research will show how amphibious mammals receive and perceive acoustic information in background noise. OBJECTIVESImprove understanding of hearing in pinnipeds by extending psychoacoustic profiles of sound reception obtained from simplified auditory processing tasks to those describing performance under increasingly complex acoustic conditions. Relate laboratory measurements to concurrent field studies of communication in fluctuating natural noise backgrounds. Strengthen predictive models that describe how signal structure and noise environments interact to constrain auditory performance, and develop weighting functions that can be used for species-typical acoustic risk assessments. APPROACHPsychoacoustic measurements of hearing are obtained from California sea lions, harbor seals, and northern elephant seals under highly controlled laboratory conditions. Long-term captive subjects are trained using operant conditioning procedures to report the presence or absence of auditory signals in noisy or quiet backgrounds. Testing takes place both under water (in a mapped, reverberant acoustic field) and in air (in a sound-attenuating hemi-anechoic chamber) because the sensitivity and frequency range of hearing in pinnipeds varies significantly as a function of medium. The stimuli presented during testing comprise synthetic and natural sounds that are systematically varied in spectral complexity, or in referential meaning established through explicit associative learning paradigms. The general approach is to obtain absolute detection thresholds for specific complex sounds and compare these thresholds to those previously obtained for pure-tone signals. The tasks are then repeated against a variety of synthetic and natural background masking stimuli to determine the signal-to-noise ratios that limit auditory detection, and in some cases, auditory recognition. The methods are modeled in