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Ice-breeding seals use vocal communication mainly during breeding season. The vocal function of aquatic mating, ice-associated ribbon seals (Histriophoca fasciata) has been unknown since they produce sounds in both breeding and non-breeding seasons. We examined the timing of their vocal presence in relation to environmental factors to infer the function of their calls in the Nemuro Strait, northern Japan, since this area is the possible southern limit of their breeding range. Vocalizations of ribbon seals were irregularly sampled from November 2012 to March 2014 in the Nemuro Strait and were compared with sea ice presence, time of day, and tidal currents. Ribbon seal downsweeps were detected in February 2013 and March 2014 only when sea ice was present along the Shiretoko Peninsula in the strait, with more detections in March leading up to the spring breeding season. Downsweep detections decreased in the middle of the day, indicating that ribbon seals were likely to be hauled out during this time. Vocalizing at night and early morning would probably reflect the increased opportunity for attracting females underwater. Our study suggests that the seal vocalizations in concurrence with sea ice presence in the Nemuro Strait could function as underwater communication for breeding.

Fin whales (Balaenoptera physalus) undergo seasonal migration in the Arctic Sea. Because their migration and distribution is likely affected by changes in global climate, we aimed to examine the migration timing of fin whales, and the relationship with prey availability within the oceanographic environment of the Arctic Sea, using passive and active acoustic monitoring methods. Automatic Underwater Sound Monitoring Systems were deployed in the southern Chukchi Sea from July 2012 to 2014 to determine the acoustic presence of fin whales. Furthermore, water temperature and salinity were recorded by a fixed data logger. An Acoustic Zooplankton Fish Profiler was additionally deployed to estimate prey abundance through backscattering strength. Sea ice concentrations were obtained by remote sensing data. Fin whale calls were automatically detected using a custom-made software, and the per cent of half-hours containing calls were counted. Fin whale calls were detected from 4 August to 20 October 2012 (78 d) and 25 July to 1 November 2013 (100 d). The extended period of acoustic presence of fin whales during 2013 when compared with 2012 is likely related to a longer ice-free period during 2013. Furthermore, generalized linear model analyses showed that half-hour periods containing calls increased with a rise in water temperature and zooplankton abundance during the initial call presence period, while they decreased with a decrease in water temperature and salinity during the end of the call presence period. Our results suggest that the rise in water temperature and zooplankton abundance affect the timing of migration of fin whales in a way that is consistent with the expansion of their suitable habitats and the extension of their presence in the Arctic Sea.

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.

Environmental changes are considered to affect the migration and distribution of baleen whales in the Arctic region. We examined the seasonal acoustic presence of fin whales (Balaenoptera physalus) and the relationships between acoustics and oceanographic environments in the southern Chukchi Sea from July 2012 to October 2015. Fin whale calls were detected from 4 August to 20 October 2012, from 25 July to 1 November 2013, from 26 July to 14 November 2014, and 7 June 2015, only in the ice-free (sea ice concentration = 0%) periods. In addition, from the recordings in 2012 and 2013, fin whale calls were present in the periods of high prey abundance, and there were significant positive correlations among their call presence, prey abundance, water temperature and salinity. Furthermore, the result that the calls were detected in 7 June 2015 suggests that fin whales arrive much earlier at the southern Chukchi Sea than previously reported. Our study provide valuable information to assess the impact on marine ecosystem in the Arctic region by environmental changes.