Pacific walrus vocal repertoire in the northeastern Chukchi Sea: Call type description and relative proportion in time and space

Abstract

Pacific walrus are present in the northeastern Chukchi Sea (NCS) from June to October. The study of their sounds has been largely restricted to the knock and bell sounds produced by males during the breeding season and in-air grunts and barks from mother and pups. A passive acoustic monitoring program conducted in the NCS since July 2006 has brought strong evidence that the underwater vocal repertoire of walrus is more diverse. Nine call types (including knocks and bells) and their variants identified over four years of acoustic monitoring will be described. Spectral measurements along with estimates of variability for high signal-to-noise ratio calls will be provided. The relative proportion of each call type across the study area and throughout the season is currently analyzed based on the identification of all calls in samples recorded multiple times per day in 2009 and 2010. Preliminary results suggest that the vocal repertoire of walrus is dominated by grunt-type calls, which is consistent with the NCS herds being mainly composed of females, pups and juveniles. The recurrent presence of knocking sounds indicates that either adult males routinely occur in the study area or that other age and sex classes also produce this call type.