Communication sounds of wild narrow-ridged finless porpoises (Neophocaena asiaeorientalis) in Ise Bay, Japan

Captive condition sometimes evokes behaviors that are not observed in animals in the wild. A confirmation of the behaviors in the wild is needed to exclude the possibility of captivity-specific behaviors. Narrow-ridged finless porpoises are reported to produce two sound types for communication: "packet sound", which is a series of pulses with repeated pulse packets (a sound series consisting of a few pulses with irregular, short inter-pulse intervals), and "burst pulses", which are a pulse train with significantly shorter inter-pulse intervals compared to packet sound. Burst pulses were reported from wild narrow-ridged finless porpoises of Seto Inland Sea-Hibiki Nada population in Japan, while the packet sound was only recorded in captive conditions. Here, we report the packet sound as well as burst pulses from wild narrow-ridged finless porpoises of Ise-Mikawa Bays population in Japan. We found six packet sounds and six burst pulses out of 5 h recording of a self-contained underwater sound recorder, at a frequency of 0.020 times/min for each sound type. It is suggested that packet sound is produced by not only captive but wild narrow-ridged finless porpoises. Future studies should focus on the behavioral state when producing communication sounds.