Seasonal trends in acoustic detection of ribbon seal (Histriophoca fasciata) vocalizations in the Bering Sea

The seasonal presence of ribbon seals (Histriophoca fasciata) on the central and southeastern Bering Sea shelf was determined from vocalizations recorded with a Passive Aquatic Listening (PAL) recorder at two sites along the 70-m isobath from 2007 to 2010. Ribbon seal vocalizations were identified as intense, stereotyped downsweeps, roars, and grunts. Acoustic detections were sea-sonal, with peak acoustic activity occurring in April at the southeastern site and May at the cen-tral shelf location. Ribbon seal acoustic presence was tightly coupled to sea ice presence, and onset of detection was associated with thicker, more extensive ice cover compared to the other Arctic pinnipeds (bearded seals [Erignathus barbatus] and walrus [Odobenus rosmarus]) detected in the region. Ribbon seal vocalizations were detected only when ice cover in the area exceeded 80%, suggesting that this species has a habitat prefer-ence or requirement for a more stable ice platform for some activities during the winter breeding season.