Diversity of marine mammal vocalizations off Rausu, Shiretoko, northern Japan

A number of marine mammal species travel off Rausu, Shiretoko as feeding and breeding habitats, providing resources for tourism. However, seasonal sea ice and severe weather conditions have restricted visual observations of marine mammals off Rausu except for daytime observations between spring and fall. To compensate for this lack of information, fixed passive acoustic recording devices were deployed to monitor the presence of marine mammals during November 2012–March 2014. Pacific white-sided dolphin (Lagenorhynchus obliquidens) burst pulsed calls in July, November, and December; ribbon seal (Histriophoca fasciata) downsweeps in February and March; killer whale (Orcinus orca) pulsed calls from April to August; and sperm whale (Physeter macrocephalus) clicks in July and August were detected. Cetacean species were possibly involved in foraging since their pulsed calls or clicks were often detected during foraging. In contrast, ribbon seals were possibly involved in breeding behaviours as seal vocalizations are likely related to breeding activities. This passive acoustic monitoring will provide new insights into the ecology of diverse marine mammals off Rausu.