Characterizing the acoustic behavior of free-ranging Risso’s dolphins (Grampus griseus) in Monterey Bay, California

Abstract

Risso’s dolphins (Grampus griseus) are a common, highly vocal odontocete species found in Monterey Bay, California, that is relatively understudied acoustically. Although several studies have focused on Risso’s echolocation, there is little research on the other social sound types for this species. Apart from echolocation clicks, the two most common sound types in Risso’s dolphin repertoires are whistles and whistle + burst pulse (whistle BP) vocalizations. In summer 2017, single C57 omnidirectional hydrophone (Cetacean Research Technology) deployments were conducted in Monterey Bay to record Risso’s sound production during periods of slow travel and social interaction at the surface. Group composition information and surface behavioral events were also recorded to provide behavioral context. Average group sizes consisted of approximately 30 animals. We completed a total of 62 h on effort and 75 deployments. Of the 5 total hours of recordings, 43% contained vocalizations. We will describe the acoustic parameters of recorded whistle and whistle BP vocalizations of Monterey Bay Risso’s dolphins, evaluate sound production rate in relationship to surface active behavior, and compare vocalizations with those of geographically isolated populations as well as sympatric odontocete species in the Bay.