Yoko Mitani | Kyoto University (original) (raw)

Papers by Yoko Mitani

Polar Biology

The number of migrating fin whales (Balaenoptera physalus) appears to be increasing in the Pacifi... more The number of migrating fin whales (Balaenoptera physalus) appears to be increasing in the Pacific Arctic after changes in the marine ecosystem and recovering from depletion by commercial whaling. Fin whale songs are sequences of sounds produced repeatedly, and they may be used for population structure assessments. However, little is known about song types and population structures in the Pacific Arctic. We recorded fin whale songs using a fixed passive acoustic monitoring system from July 2012 to June 2015 in the southern Chukchi Sea. We randomly selected one hour of data from each week of the study period and measured the inter-pulse intervals (IPIs) of the songs. Songs were detected from August to November 2012-2014. All 1✉ 1 2 1 2 songs had a sequence of doublets with two IPIs (10.5 and 19.6 s), and they were similar to previously reported songs of whales from the eastern North Pacific in 2001-2013 but differed from those of whales from the Bering Sea and northeastern Chukchi Sea in 2007-2010. These results suggest that one group of fin whales migrated to the southern Chukchi Sea from the eastern North Pacific in 2012-2014, or the song changed. Comparing songs from different areas of the Pacific Arctic during the same years will reveal whether this group dispersed in this area.

Aquatic Mammals

We report the first case of conspecific calf-directed aggression in Pacific white-sided dolphins ... 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...

Fisheries Science, 2022

To understand the environmental factors affecting the density of foraging seabirds across the col... 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.

2016 Techno-Ocean (Techno-Ocean), 2016

Environmental changes are considered to affect the migration and distribution of baleen whales in... 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.

Mammal Study, 2021

Abstract. In this study, we examined a genetic variation of killer whales, Orcinus orca, from off... 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.

Recent studies on diving and foraging behavior of three species of toothed whales: the sperm whal... 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 ...

2016 Techno-Ocean (Techno-Ocean), 2016

A number of marine mammal species travel off Rausu, Shiretoko as feeding and breeding habitats, p... 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...

Diving behaviour of sei whales and vertical distribution of their prey were recorded simultaneous... 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...

IWC Journal of Cetacean Research and Management, 2019

Animal-borne electronic instruments (tags) are valuable tools for collecting information on cetac... 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...

Mammal Research, 2021

Competition between Kuril harbor seals (Phoca vitulina stejnegeri) and salmon set-net fishing ind... more Competition between Kuril harbor seals (Phoca vitulina stejnegeri) and salmon set-net fishing industries has become a serious problem with the recent increase in the number of seals in Erimo, Hokkaido, Japan. We aimed to understand the detailed dietary structure of Kuril harbor seals focusing on intraspecific differences and verify whether "problem seals" who habitually use salmon set-nets could be characterized by intrinsic factors such as sex and maturity. We estimated the diet of Kuril harbor seals in two fishing seasons using DNA barcoding diet analysis on colon contents and verified intraspecific differences in their diet. In spring, their diets showed different tendencies between maturity stage; each adult seal fed on different prey items, suggesting that they avoid the intra-species competition over food during the breeding season. Additionally, it was implied that some adult females habitually stole from salmon set-nets. Our dietary analysis showed dietary changes of Kuril harbor seals with different tendencies depending on maturity or sex, suggesting that problem individuals who habitually use set-nets can be characterized by intrinsic factors. This detailed dietary information can offer an accurate assessment of seal predation effects on fishing targets and the selective management of Kuril harbor seals, especially in mitigating seal-commercial fishery conflicts.

Polar Biology, 2019

The seasonal habitat use of bearded seals is important information in terms of conservation of th... more The seasonal habitat use of bearded seals is important information in terms of conservation of this species. However, their distribution outside the breeding season has not been well documented. We investigated seasonal variations in the call occurrence of bearded seals by using passive acoustic monitoring in the southern Chukchi Sea, which has some of the greatest benthic biomass in the Pacific sector of the Arctic Ocean. Underwater sounds were recorded between 2012 and 2015. Calls of bearded seals were detected from mid-September or early October to the end of each recording period (mid-May 2013, early March 2014, and mid-June 2015). Two peaks in call occurrence were noted; the first peak occurred during the open-water periods in November, and the second peak occurred during icecovered periods. This suggest that bearded seals utilize the southern Chukchi Sea not only for the breeding site but also for the autumn foraging site. We could complement the information about the southward autumn migration pattern of bearded seals, and the southern Chukchi Sea was suggested as the south limit of bearded seals' autumn distribution. Additionally, their vocal activity during autumn in this site was suggested to have some role in social interaction. Our results indicated that the southern Chukchi Sea would be an important monitoring site for understanding the habitat use and the vocal activity of bearded seals especially outside the breeding season.

Pacific Science, 2017

Hydrographic, hydroacoustic, and cetacean visual surveys were conducted using a quantitative echo... more Hydrographic, hydroacoustic, and cetacean visual surveys were conducted using a quantitative echosounder to estimate environmental factors influencing migration timing and distribution of Pacific white-sided dolphins (Lagenorhynchus obliquidens) in the Tsugaru Strait (nonbreeding area) and Funka Bay (breeding area) near Hokkaido, Japan. Higher numbers of dolphins were observed in the Tsugaru Strait during May and June and in Funka Bay during June, July, and August. Potential prey were observed in the Tsugaru Strait in May, June, and August, but they may not have been of a suitable size in August, which may explain absence of the dolphins in that month. In Funka Bay, potential prey were abundant in May, but dolphins may have been absent because of small prey size and low water temperature. In a smaller-scale analysis, the relationship between dolphins and prey was different in the two areas, with dolphin distribution more closely associated with prey distribution in the Funka Bay breeding area. This difference may have resulted from mothers needing to feed more frequently during lactation. These data should serve as an important foundation for estimating environmental factors impacting small cetaceans around Japan as well as changing environmental factors during the cetacean life cycle.

Polar Science, 2016

Abstract Gray whales (Eschrichtius robustus) are distributed within the productive neritic and es... 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.

The Journal of the Acoustical Society of America, 2016

Vocalizations of ice-breeding ribbon seals Histriophoca fasciata were recorded using underwater p... 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...

Zoological Science, 2016

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

ICES Journal of Marine Science, 2016

Fin whales (Balaenoptera physalus) undergo seasonal migration in the Arctic Sea. Because their mi... 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...

Ecology and Evolution, 2017

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Polar Biology

The number of migrating fin whales (Balaenoptera physalus) appears to be increasing in the Pacifi... more The number of migrating fin whales (Balaenoptera physalus) appears to be increasing in the Pacific Arctic after changes in the marine ecosystem and recovering from depletion by commercial whaling. Fin whale songs are sequences of sounds produced repeatedly, and they may be used for population structure assessments. However, little is known about song types and population structures in the Pacific Arctic. We recorded fin whale songs using a fixed passive acoustic monitoring system from July 2012 to June 2015 in the southern Chukchi Sea. We randomly selected one hour of data from each week of the study period and measured the inter-pulse intervals (IPIs) of the songs. Songs were detected from August to November 2012-2014. All 1✉ 1 2 1 2 songs had a sequence of doublets with two IPIs (10.5 and 19.6 s), and they were similar to previously reported songs of whales from the eastern North Pacific in 2001-2013 but differed from those of whales from the Bering Sea and northeastern Chukchi Sea in 2007-2010. These results suggest that one group of fin whales migrated to the southern Chukchi Sea from the eastern North Pacific in 2012-2014, or the song changed. Comparing songs from different areas of the Pacific Arctic during the same years will reveal whether this group dispersed in this area.

Aquatic Mammals

We report the first case of conspecific calf-directed aggression in Pacific white-sided dolphins ... 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...

Fisheries Science, 2022

To understand the environmental factors affecting the density of foraging seabirds across the col... 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.

2016 Techno-Ocean (Techno-Ocean), 2016

Environmental changes are considered to affect the migration and distribution of baleen whales in... 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.

Mammal Study, 2021

Abstract. In this study, we examined a genetic variation of killer whales, Orcinus orca, from off... 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.

Recent studies on diving and foraging behavior of three species of toothed whales: the sperm whal... 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 ...

2016 Techno-Ocean (Techno-Ocean), 2016

A number of marine mammal species travel off Rausu, Shiretoko as feeding and breeding habitats, p... 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...

Diving behaviour of sei whales and vertical distribution of their prey were recorded simultaneous... 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...

IWC Journal of Cetacean Research and Management, 2019

Animal-borne electronic instruments (tags) are valuable tools for collecting information on cetac... 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...

Mammal Research, 2021

Competition between Kuril harbor seals (Phoca vitulina stejnegeri) and salmon set-net fishing ind... more Competition between Kuril harbor seals (Phoca vitulina stejnegeri) and salmon set-net fishing industries has become a serious problem with the recent increase in the number of seals in Erimo, Hokkaido, Japan. We aimed to understand the detailed dietary structure of Kuril harbor seals focusing on intraspecific differences and verify whether "problem seals" who habitually use salmon set-nets could be characterized by intrinsic factors such as sex and maturity. We estimated the diet of Kuril harbor seals in two fishing seasons using DNA barcoding diet analysis on colon contents and verified intraspecific differences in their diet. In spring, their diets showed different tendencies between maturity stage; each adult seal fed on different prey items, suggesting that they avoid the intra-species competition over food during the breeding season. Additionally, it was implied that some adult females habitually stole from salmon set-nets. Our dietary analysis showed dietary changes of Kuril harbor seals with different tendencies depending on maturity or sex, suggesting that problem individuals who habitually use set-nets can be characterized by intrinsic factors. This detailed dietary information can offer an accurate assessment of seal predation effects on fishing targets and the selective management of Kuril harbor seals, especially in mitigating seal-commercial fishery conflicts.

Polar Biology, 2019

The seasonal habitat use of bearded seals is important information in terms of conservation of th... more The seasonal habitat use of bearded seals is important information in terms of conservation of this species. However, their distribution outside the breeding season has not been well documented. We investigated seasonal variations in the call occurrence of bearded seals by using passive acoustic monitoring in the southern Chukchi Sea, which has some of the greatest benthic biomass in the Pacific sector of the Arctic Ocean. Underwater sounds were recorded between 2012 and 2015. Calls of bearded seals were detected from mid-September or early October to the end of each recording period (mid-May 2013, early March 2014, and mid-June 2015). Two peaks in call occurrence were noted; the first peak occurred during the open-water periods in November, and the second peak occurred during icecovered periods. This suggest that bearded seals utilize the southern Chukchi Sea not only for the breeding site but also for the autumn foraging site. We could complement the information about the southward autumn migration pattern of bearded seals, and the southern Chukchi Sea was suggested as the south limit of bearded seals' autumn distribution. Additionally, their vocal activity during autumn in this site was suggested to have some role in social interaction. Our results indicated that the southern Chukchi Sea would be an important monitoring site for understanding the habitat use and the vocal activity of bearded seals especially outside the breeding season.

Pacific Science, 2017

Hydrographic, hydroacoustic, and cetacean visual surveys were conducted using a quantitative echo... more Hydrographic, hydroacoustic, and cetacean visual surveys were conducted using a quantitative echosounder to estimate environmental factors influencing migration timing and distribution of Pacific white-sided dolphins (Lagenorhynchus obliquidens) in the Tsugaru Strait (nonbreeding area) and Funka Bay (breeding area) near Hokkaido, Japan. Higher numbers of dolphins were observed in the Tsugaru Strait during May and June and in Funka Bay during June, July, and August. Potential prey were observed in the Tsugaru Strait in May, June, and August, but they may not have been of a suitable size in August, which may explain absence of the dolphins in that month. In Funka Bay, potential prey were abundant in May, but dolphins may have been absent because of small prey size and low water temperature. In a smaller-scale analysis, the relationship between dolphins and prey was different in the two areas, with dolphin distribution more closely associated with prey distribution in the Funka Bay breeding area. This difference may have resulted from mothers needing to feed more frequently during lactation. These data should serve as an important foundation for estimating environmental factors impacting small cetaceans around Japan as well as changing environmental factors during the cetacean life cycle.

Polar Science, 2016

Abstract Gray whales (Eschrichtius robustus) are distributed within the productive neritic and es... 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.

The Journal of the Acoustical Society of America, 2016

Vocalizations of ice-breeding ribbon seals Histriophoca fasciata were recorded using underwater p... 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...

Zoological Science, 2016

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

ICES Journal of Marine Science, 2016

Fin whales (Balaenoptera physalus) undergo seasonal migration in the Arctic Sea. Because their mi... 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...

Ecology and Evolution, 2017

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.