Critical bandwidth measurements in pinnipedsa)

Auditory masking occurs when one sound interferes with the detection of another. While knowledge of this sensory phenomenon is growing, much of our understanding remains theoretical or based on terrestrial models. Empirical data become especially important when considering hearing in marine mammals that rely heavily on acoustic cues for foraging, communicating, and avoiding predation. To better understand how anthropogenic noise can influence hearing in otariid, odobenid, and phocid pinnipeds, detection thresholds for tonal sounds were measured for a trained California sea lion, Pacific walrus, bearded seal, and spotted seal within noise of progressively constrained spectral content. The frequency bandwidth of noise that contributed to the masking of a given tone (the "critical bandwidth") was identified at up to six frequencies between 100 and 16 000 Hz. Absolute critical bandwidth values increased with increasing frequency in all four species, although taxon-level trends were apparent. The sea lion and walrus showed similar auditory adaptation to noise, with critical bandwidths ranging from 16%-35% and 21%-43% of center frequency, respectively. Critical bandwidths were narrower in both phocids, ranging from 14%-29% of center frequency across tested frequencies; particularly narrow bandwidths at 500 Hz and below suggest additional auditory specialization for seals at lower frequencies.