Yoko Mitani
Kyoto University, Wildlife Research Center, Faculty Member
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We report the first case of conspecific calf-directed aggression in Pacific white-sided dolphins (Lagenorhynchus obliquidens) as a possible infanticide attempt in Mutsu Bay, Japan. Our observation of a 75-minute-long persistent attack on... more
We report the first case of conspecific calf-directed aggression in Pacific white-sided dolphins (Lagenorhynchus obliquidens) as a possible infanticide attempt in Mutsu Bay, Japan. Our observation of a 75-minute-long persistent attack on a neonate was performed by 10 attackers (4 adult males, 1 possible male, and 5 of unknown sex) and left the neonate with visible injuries. Only one individual was recorded for the entirety of the event and was regarded as the possible mother, displaying protective behaviours towards the neonate as well as being the target of coercive guarding and sexual behaviours, such as mounting, by the attackers. The observation featured a distinct group composition change in which, after 50 minutes, the attack was taken over by a new group of attackers. There was a brief overlap between the groups in which some dolphins from the first group surfaced with the second. Excluding the mother and calf, only two individuals that were observed towards the end of the fi...
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To understand the environmental factors affecting the density of foraging seabirds across the cold-water belt in the southwestern Okhotsk Sea, we conducted a 1-day (180-km transect length) shipboard seabird survey off the northeastern... more
To understand the environmental factors affecting the density of foraging seabirds across the cold-water belt in the southwestern Okhotsk Sea, we conducted a 1-day (180-km transect length) shipboard seabird survey off the northeastern coast of Hokkaido during summer in 2019, along with acoustic observations of potential prey (zooplankton and fish) biomass, thermosalinograph measurements, and CTD observations. Planktivorous short-tailed shearwaters Ardenna tenuirostris (66% of total seabirds) and piscivorous rhinoceros auklets Cerorhinca monocerata (28%) were predominant, but foraged in contrasting habitats. A large foraging flock of shearwaters was observed in the cold-water belt zone, including its front with coastal Soya Warm Current Water and the offshore Fresh Surface Okhotsk Sea Water, where surface chlorophyll a concentrations were the highest but not related to their prey (zooplankton) biomass at any spatial scale between 4.6 and 9.2 km. In contrast, the density of auklets was high in the coastal Soya Warm Current Water, where the acoustically determined fish biomass was large, and showed a positive relationship with the fish biomass especially in the lower layer (29–104 m depth) at any spatial scale. This species-specific difference in response to prey biomass might be related to prey-searching behaviors; i.e., rhinoceros auklets search prey underwater visually, but short-tailed shearwater can use both visual and olfactory cues to locate zooplankton patches from the air.
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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... more
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.
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Abstract. In this study, we examined a genetic variation of killer whales, Orcinus orca, from off the coast of Hokkaido, Japan, by sequencing the D-loop and cytochrome b (Cyt-b) regions of the mitochondrial genome. Three D-loop and two... more
Abstract. In this study, we examined a genetic variation of killer whales, Orcinus orca, from off the coast of Hokkaido, Japan, by sequencing the D-loop and cytochrome b (Cyt-b) regions of the mitochondrial genome. Three D-loop and two Cyt-b haplotypes were identified from eight skin biopsies. These five haplotypes had been previously deposited at GenBank and the International Nucleotide Sequence Database Collaboration (INSDC). Two D-loop and one Cyt-b haplotypes were consistent with the marine mammal-eating “Transient” ecotype previously reported in Japanese waters. One D-loop and one Cyt-b haplotypes were identified as the fish-eating “Resident” or “Offshore” ecotype that is the first record of this ecotype in Japanese waters. Our study showed that different ecotypes exist in Japanese waters, contributing to the conservation and management of killer whales.
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Recent studies on diving and foraging behavior of three species of toothed whales: the sperm whale, Cuvier's beaked whale and Blainville's beaked whale, are introduced. Their characteristic diving behaviors are summarized,... more
Recent studies on diving and foraging behavior of three species of toothed whales: the sperm whale, Cuvier's beaked whale and Blainville's beaked whale, are introduced. Their characteristic diving behaviors are summarized, compared and discussed. Despite a smaller physiological capacity of diving, Cuvier's beaked whales and Blainville's beaked whales forage smaller prey items at higher frequencies (28.9/dive and 27.8/dive) in deeper waters, whereas sperm whales forage larger prey, mostly squids, at lower frequency in shallower waters than the two beaked whales. The two species of beaked whales regularly exceeded their calculated ADL in their deep foraging dives, but sperm whales dived within their calculated ADL. The obvious differences in foraging depth and prey size of these three species indicate possible changes in mesopelagic prey fauna with depth. Introduction It is widely confirmed that many marine endotherms dive deep and long (Table 1). Since some birds can ...
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... more
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 behaviou...
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Diving behaviour of sei whales and vertical distribution of their prey were recorded simultaneously in 2013 JARPNII to study their feeding behaviour at micro scale. This was the first attempt of this kind of observation targeting on this... more
Diving behaviour of sei whales and vertical distribution of their prey were recorded simultaneously in 2013 JARPNII to study their feeding behaviour at micro scale. This was the first attempt of this kind of observation targeting on this species. Small acoustic time depth transmitters (pingers) were attached to two sei whales and their behaviours were recorded for 10.2 and 32.0 hours, respectively. Vertical distributions and densities (volume backscattering strength, SV) of their prey were recorded by an echosounder following swimming path of the individuals. The diving behaviour deeper than 10 m was classified into two shapes (U-shape, V-shape). It was assumed that U-shape was related to feeding behaviour, especially lunge feeding, while V-shape was related to prey searching dive. Sei whales showed diel patterns in mean diving depth (day: 19 ± 14 m and 16 ± 10 m, night: 12 ± 5 m and 10 ± 5 m). Dense scattering layers (presumably zooplankton) were observed around 40 m during the day...
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Animal-borne electronic instruments (tags) are valuable tools for collecting information on cetacean physiology, behaviour and ecology, and forenhancing conservation and management policies for cetacean populations. Tags allow researchers... more
Animal-borne electronic instruments (tags) are valuable tools for collecting information on cetacean physiology, behaviour and ecology, and forenhancing conservation and management policies for cetacean populations. Tags allow researchers to track the movement patterns, habitat use andother aspects of the behaviour of animals that are otherwise difficult to observe. They can even be used to monitor the physiology of a taggedanimal within its changing environment. Such tags are ideal for identifying and predicting responses to anthropogenic threats, thus facilitating thedevelopment of robust mitigation measures. With the increasing need for data best provided by tagging and the increasing availability of tags, suchresearch is becoming more common. Tagging can, however, pose risks to the health and welfare of cetaceans and to personnel involved in taggingoperations. Here we provide ‘best practice’ recommendations for cetacean tag design, deployment and follow-up assessment of tagged i...
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Abstract Gray whales (Eschrichtius robustus) are distributed within the productive neritic and estuarine waters of the North Pacific Ocean, the Bering Sea, and adjacent waters of the Arctic Ocean. They migrate to high-latitude feeding... more
Abstract Gray whales (Eschrichtius robustus) are distributed within the productive neritic and estuarine waters of the North Pacific Ocean, the Bering Sea, and adjacent waters of the Arctic Ocean. They migrate to high-latitude feeding grounds each spring. Their main feeding grounds in the Arctic include the Chirikov Basin, the northeastern Chukchi Sea from Pt. Hope to Cape Lisburne and Pt. Lay to Pt. Barrow, and the northwestern Chukchi Sea along the Chukotka coast. Although sightings are rare in the Canadian Beaufort Sea, we observed three gray whales in two groups in this area in September 2014. A mud plume was observed near one of the whales, suggesting the animal had been feeding. In the Alaskan Beaufort Sea, large-scale monitoring of the distributions of marine mammals has been continuously conducted since 1979; however, there has been less monitoring in the Canadian Beaufort Sea. Therefore, it is necessary to record opportunistic sightings, such as those described here.
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Vocalizations of ice-breeding ribbon seals Histriophoca fasciata were recorded using underwater passive acoustic methods from November 2012 to March 2014 off the Nemuro Strait, Japan. Seal presence in the strait was examined in relation... more
Vocalizations of ice-breeding ribbon seals Histriophoca fasciata were recorded using underwater passive acoustic methods from November 2012 to March 2014 off the Nemuro Strait, Japan. Seal presence in the strait was examined in relation to the sea ice extent in the Okhotsk Sea. Ribbon seal downsweeps were only detected when sea ice was present in the strait (February and March), with more detections in March leading up to the spring breeding season. Since ribbon seals require ice for breeding, underwater communication for breeding could be needed during the sea ice presence in this strait. Northeasterly winds were another indirect driver of ribbon seal occurrence, since winds from this direction likely transport sea ice from the central Okhotsk Sea into the Nemuro Strait. Downsweep detections decreased in the middle of the day, which is consistent with observations that seals hauled out on the ice during this time, and thus were producing fewer underwater vocalizations. Our results suggest that a decrease...
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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... more
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 Oc...
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ABSTRACT Two closely related baleen whale species, sei and Bryde's whales, in the western North Pacific were studied to identify differences in habitat use. Data were obtained from May to August 2004 and 2005. This study examined... more
ABSTRACT Two closely related baleen whale species, sei and Bryde's whales, in the western North Pacific were studied to identify differences in habitat use. Data were obtained from May to August 2004 and 2005. This study examined the relationship between oceanographic features derived from satellite data and the distribution of sei and Bryde's whales using basic statistics. We investigated oceanographic features including sea surface temperature (SST), sea surface chlorophyll a (Chl-a), sea surface height anomalies (SSHAs), and depth of the habitat. These two whale species used habitats with different SST, Chl-a, and SSHA ranges. The 0.25 mg m−3 Chl-a contour (similar to the definition of the Transition Zone Chlorophyll Front) was a good indicator that separated the habitats of sei and Bryde's whales. Then generalized linear models were used to model the probabilities that the whale species would be present in a habitat and to estimate their habitat distribution throughout the study area as a function of environmental variables. The potential habitats of the two species were clearly divided, and the boundary moved north with seasonal progression. The habitat partitioning results indicated that SST contributed to the patterns of habitat-use and might reflect differences in prey species between the two whales. This study showed that the habitats of the sei and Bryde's whales were clearly divided and their potential habitat-use changed seasonally.
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ABSTRACT Page 1. Aquatic Mammals 2013, 39(4), 378-384, DOI 10.1578 / AM . 39.4 . 2013.378 Detection of Grooming Behaviours with an Acceleration Data Logger in a Captive Northern Fur Seal (Callorhinus ursinus) Takashi Iwata,1 Shiroh... more
ABSTRACT Page 1. Aquatic Mammals 2013, 39(4), 378-384, DOI 10.1578 / AM . 39.4 . 2013.378 Detection of Grooming Behaviours with an Acceleration Data Logger in a Captive Northern Fur Seal (Callorhinus ursinus) Takashi Iwata,1 Shiroh Yonezaki,2 Kaoru Kohyama,3 and Yoko Mitani4 ...
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Spatial niche partitioning of marine mammals is thought to be caused by dietary differences. However, due to the difficulty involved with conducting simultaneous marine predator and prey distribution surveys at the same scale, marine... more
Spatial niche partitioning of marine mammals is thought to be caused by dietary differences. However, due to the difficulty involved with conducting simultaneous marine predator and prey distribution surveys at the same scale, marine mammals have not been studied alongside their prey distribution. To understand the spatial niche overlap between 3 small cetaceans observed in the eastern coastal waters of Hokkaido, Japan (Pacific white-sided dolphin Lagenorhynchus obliquidens, Dall’s porpoise Phocoenoides dalli, and harbor porpoise Phocoena phocoena), and the mechanisms behind the differences in their distributions, visual and hydroacoustic surveys using a quantitative echosounder were concurrently conducted. A clear spatial niche overlap was observed between the Pacific white-sided dolphin and Dall’s porpoise, whereas the spatial overlap was moderate between the harbor porpoise and the other 2 species. In areas where Pacific white-sided dolphins were observed, potential prey was abun...
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The distribution and abundance of marine debris were investigated by visual survey and a neuston net in the North Pacific and Bering Sea during the T/S Oshoro Maru cruise from June to August 2012. The observed debris included pieces of... more
The distribution and abundance of marine debris were investigated by visual survey and a neuston net in the North Pacific and Bering Sea during the T/S Oshoro Maru cruise from June to August 2012. The observed debris included pieces of plastic, plastic and glass bottles, metallic objects, glass, and fishing gear. The concentrations of plastic sampled by a neuston net were higher in the Transition Zone than those in the Subarctic North Pacific and Bering Sea. The abundance and weight of these small plastic pieces collected by a neuston net did not significantly increase from 1980s. Long-term monitoring and information sharing are important in concert with related countries and organizations.
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Antarctic minke whales (Balaenoptera bonaerensis) are migratory capital breeders that experience intensive summer feeding on Antarctic krill (Euphausia superba) in the Southern Ocean and winter breeding at lower latitudes, but their prey... more
Antarctic minke whales (Balaenoptera bonaerensis) are migratory capital breeders that experience intensive summer feeding on Antarctic krill (Euphausia superba) in the Southern Ocean and winter breeding at lower latitudes, but their prey outside of the Antarctic is unknown. Stable isotope analyses were conducted on δ13C and δ15N from the baleen plates of ten pregnant Antarctic minke whales to understand the growth rate of the baleen plate and their diet in lower latitudes. Two to three oscillations along the length of the edge of the baleen plate were observed in δ15N, and the annual growth rate was estimated to be 75.2 ± 20.4 mm, with a small amplitude (0.97 ± 0.21 ‰). Bayesian stable isotope mixing models were used to understand the dominant prey that contributed to the isotopic component of the baleen plate using Antarctic krill from the stomach contents and reported values of Antarctic coastal krill (Euphausia crystallorophias), Antarctic silver fish (Pleuragramma antarcticum), ...
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Diving Costs and Prey Availability of Weddell Seals: Comparisons of Three-Dimensional Dive Paths and Image Data between Two Breeding Colonies (Open Symposium for Public on New Marine Biology Using Micro-Biologging Methods, PROCEEDING OF THE 74^< TH> ANNUAL MEETING OF THE ZOOLOGICAL SOCIETY OF JAPAN)more