Underwater hearing thresholds in pinnipeds measured over a 6-year period

Abstract

While absolute hearing thresholds have been obtained for some marine mammals, few published data are available on how measurements of individual auditory sensitivity may change over relatively long periods of time. Studies that have investigated temporal changes in sensitivity have typically focused on animals in which differences in hearing are anticipated (age-related hearing loss). This study investigated the replicability of underwater hearing thresholds in prime-aged individuals of three pinniped species over a 6-year period. Aside from their age and experience with behavioral signal detection tasks, test subjects were of similar physical condition throughout this experiment. They were tested in the same enclosure at similar test frequencies (0.1–6.4 kHz) using identical methodology and criteria. Underwater hearing thresholds obtained throughout this testing period were not significantly different. These data indicate that underwater hearing sensitivity may remain relatively stable over long periods in nonsenescent marine mammals, including those regularly exposed to noise. Further, our results suggest that variability in testing equipment and experimental personnel may have little impact on behavioral hearing data, as long as similar testing methodologies and subject response bias are carefully maintained.