Department of FisheriesAssociate Professor

Last Updated :2024/07/20

■Researcher comments

List of press-related appearances


■Researcher basic information

Research Keyword

  • 個体群   社会行動   鯨類   認知科学   海洋動物   イルカ   動物行動学   ハクジラ亜目   コミュニケーション   左右性   Tursiops   ミナミハンドウイルカ   

Research Field

  • Life sciences / Marine/Aquatic life sciences
  • Life sciences / Animals: biochemistry, physiology, behavioral science
  • Humanities & social sciences / Cognitive sciences
  • Life sciences / Aquaculture



  • 2015/04 - Today  Kindai UniversityDepartment of Fisheries, Faculty of AgricultureLecturer
  • 2013/12 - 2015/03  Tokai University創造科学技術研究機構日本学術振興会特別研究員(RPD)
  • 2012/04 - 2013/11  Kyoto UniversityKyoto University日本学術振興会特別研究員(RPD)
  • 2009/07 - 2012/03  The University of TokyoLife Science Network特任助教
  • 2008/04 - 2009/06  東京大学海洋研究所海洋科学国際共同研究センター特任研究員
  • 2008/01 - 2008/03  University of PretoriaCetacean Unit, Mammal Research Institute, Department of Zoology and EntomologyPost-Doctoral Fellow
  • 2005/10 - 2008/03  The University of TokyoOcean Research InstituteJSPS research fellow (PD)
  • 2005/04 - 2006/09  東京工業大学 日本学術振興会特別研究員(DC)

Educational Background

  • 2002/04 - 2006/09  東京工業大学大学院  生命理工学研究科  生体システム専攻
  • 2000/04 - 2002/03  Tokyo University of Agriculture and Technology  農学研究科  共生持続社会学専攻
  • 1996/04 - 2000/03  Tokyo University of Agriculture and Technology  Faculty of Agriculture  Department of Ecoregion Science

■Research activity information


  • 2017/01 近畿大学 近大メディアアワード2016特別賞
    受賞者: 酒井 麻衣
  • 2016/09 日本哺乳類学会 日本哺乳類学会奨励賞
    受賞者: 酒井麻衣
  • 2013/11 Editor's Choice Award 2013, Journal of Ethology
    受賞者: 酒井麻衣


  • Aoi Miyanishi; Mai Sakai; Kazunobu Kogi
    Mammal Study Mammalogical Society of Japan 48 (3) 159 - 169 1343-4152 2023/05 [Refereed]
  • Genfu Yagi; Kazunobu Kogi; Mai Sakai
    MARINE MAMMAL SCIENCE WILEY 39 (2) 662 - 670 0824-0469 2023/04 [Refereed]
    Age is an important parameter for the study of ecology and population dynamics. Current methodologies for age estimation in cetaceans generally involve invasive or postmortem techniques. They are not suitable for wild marine mammals with small populations. Our previous study shows that in Indo-Pacific bottlenose dolphins, both the number and size of body speckles increase with age. We observed speckles of 41 known-age individuals (28 females and 13 males) between the ages of 7 and 25 years using underwater video data. The ages of individuals were obtained from a long-term identification survey since 1994. Here, we created an age-estimation model using quantification theory type I analysis. The model estimated the age accurately from speckle observation (R-2 = 0.77, standard deviation of 2.58 years). We clarified the age of 89 individuals (64% of 139 unknown age individuals) near Mikura Island. This is the first study to use a noninvasive age estimation method to statistically verify its accuracy and revealed the age of the majority of the population.
  • Tadamichi Morisaka; Mai Sakai; Hiromitsu Hama; Kazunobu Kogi
    Mammalian Biology 2022/09 [Refereed]
  • Mai Sakai; Hiroshi Katsumata; Shiro Kohshima
    JOURNAL OF ETHOLOGY SPRINGER JAPAN KK 40 (3) 257 - 264 0289-0771 2022/06 [Refereed]
    Bottlenose dolphins perform flipper rubbing in which they rub their partners with their pectoral fins. Considered similar to social grooming in primates, which have social and hygienic functions, flipper rubbing has been suggested to possess certain social functions. However, there are no reports based on quantitative data to support a hygienic function of this behavior. In this study, flipper rubbing and self-rubbing were observed in a group of three captive mother-calf dolphin pairs. In 19.2% of the observed 806 flipper-to-body rubbings and 54% of the 276 self-rubbings, dead skin was shed from the rubbed body part. There was a significant negative correlation between the number of flipper-to-body rubbing episodes the subjects received and their performance of self-rubbing. These results suggest that a function of flipper rubbing is to maintain and care for the body surface. In all mother-calf pairs, the mother rubbed her calf significantly more often than the calf rubbed the mother. Furthermore, each mother became a rubber significantly more often when their own offspring was their rubbing partner than when the partner was any other individual. These findings suggest that flipper rubbing is a mother-to-calf caring behavior.
  • Genfu Yagi; Mai Sakai; Kazunobu Kogi
    MARINE MAMMAL SCIENCE WILEY 38 (1) 73 - 86 0824-0469 2022/01 [Refereed]
    Age estimating wild dolphins using noninvasive methods will improve our understanding of their ontogeny. Speckles appear on the ventral through to the lateral areas of Indo-Pacific bottlenose dolphins (Tursiops aduncus) as they age. Age-related changes in the speckle density and shape were examined using type classification. Speckles first appeared on the ventral area of the genital area at approximately 6.5 years. They increased in two specific directions, from the genital area to the jaw and from the ventral side to the lateral side. The speckle shape changed with aging from a dot-shape to oblong. Individuals aged over 35 years possessed more speckles than those aged 24-26 years. The oldest age category of dolphins in this study was over 35 years. The speckling area similarly increased with age for all individuals. Therefore, the results suggest that speckle condition can be used to estimate age. The relationship between speckling area and age showed no significant sexual dimorphism except near the genital slit area. There was no speckle area around the genital slit which differed in shape between the sexes. Therefore, speckle patch shape may be a useful sex confirmation tool.
  • Rikiya TAKAHASHI; Nozomi KOBAYASHI; Suguru HIGA; Mai SAKAI
    Japanese Journal of Zoo and Wildlife Medicine Japanese Society of Zoo and Wildlife Medicine 26 (4) 143 - 146 1342-6133 2021/12 [Refereed]
  • 長谷川雛; 酒井麻衣; 若林郁夫; 宮西葵
    哺乳類科学 61 (2) 197 - 203 0385-437X 2021 [Refereed]
  • 北夕紀; 佐々木萌美; 立川利幸; 十万仁志; 寺沢文男; 小木万布; 酒井麻衣; 村山美穂; 森阪匡通; 神田育子; 吉岡基
    DNA多型 29 (1) 2188-3815 2021 [Refereed]
  • Rikiya Takahashi; Mai Sakai; Kazunobu Kogi; Tadamichi Morisaka; Takao Segawa; Hiroshi Ohizumi
    Aquatic Mammals Aquatic Mammals Journal 46 (6) 531 - 541 0167-5427 2020/11 [Refereed]
  • Chisato Yamamoto; Nobuyuki Kashiwagi; Mika Otsuka; Mai Sakai; Masaki Tomonaga
    PEERJ PEERJ INC 7 2167-8359 2019/10 
    In comparison with terrestrial animals, such as primates, there is limited empirical evidence for cooperative behavior in marine mammals under experimental conditions. In this study, we used a cooperative rope-pulling task to investigate how bottlenose dolphins (Tursiops truncatus) coordinate their behavior with a partner. Dolphins successfully learned and were able to perform the task, even when one subject started after the other. In the no-delay condition (i.e., both subjects sent at the same time), one pair of dolphins showed coordinated behaviors. When pairs were successful in solving the task in the delay condition (i.e., one individual sent later than the other), the initiators (i.e., first individual sent) were likely to wait for the follower to arrive, and the follower was likely to swim faster when the initiator did not wait and started pulling the rope alone. These coordinated behaviors might help resolve the given cooperative task. Our results suggest that bottlenose dolphins learn to coordinate their behaviors via trial and error and recognize the necessity of performing simultaneous actions with a partner to successfully accomplish cooperative tasks. In addition, both partners showed behavioral changes over many trials of no-delay and delay conditions, suggesting that bidirectional coordination occurred in the cooperative task.
  • 酒井麻衣
    哺乳類科学 58 (1) 135 - 139 2018/07 [Invited]
  • Yoshinobu INADA; Naoki TAMIYA; Maako MIYAKE; Tadamichi MORISAKA; Mai SAKAI; Ikuo WAKABAYASHI; Masahiko KASAMATSU; Yasuhiro UEKUSA
    Journal of Biomechanical Science and Engineering 12 (3) 2017/07 [Refereed]
  • 北夕紀; 村山美穂; 小木万布; 森阪匡通; 酒井麻衣; 椎名隆
    DNA多型 25 (1) 52‐57 - 57 2188-3815 2017/07 [Refereed]
  • MIYAKE Maako; NARA Shotaro; INADA Yoshinobu; TAKAHASHI Shun; SAKAI Mai; MORISAKA Tadamichi
    Fluid dynamic effects between adjacent streamline bodies have a conspicuous role in drag reduction. One typical example is a dolphin drafting. When two dolphins such as a mother and a calf swim side by side, the calf seldom flaps its tail fin, indicating the calf utilizes the fluid dynamic force between the two bodies as a thrust. This force is generated by the Venturi effect. In this study, wind tunnel tests were conducted with two streamline bodies of different sizes that mimicked the mother and the calf dolphins to clarify the fluid dynamic effects between two bodies at various relative positions. In consequence, the increase of friction drag by the acceleration of flow between two bodies and the thrust generation by the Venturi effect were confirmed as well as the optimum position to maximize the thrust, indicating the possibility of effective design of airplanes with external appendages.
  • Kimika Tsuji; Kazunobu Kogi; Mai Sakai; Tadamichi Morisaka
    Aquatic Mammals 43 (6) 585 - 593 0167-5427 2017 [Refereed]
    © Aquatic Mammals 2017. Emigration of individual animals is an important biological phenomenon that depends on both populations and ecosystem attributes. Off Mikura Island, a long-term identification survey of individual Indo-Pacific bottlenose dolphins has been conducted since 1994 using an underwater video system. Between 1994 and 2014, 277 individual dolphins were identified by this survey, with 41 individuals emigrating from Mikura Island during this period. Adults emigrated significantly more often than younger age classes. The sex and age classes of emigrants in 2008 and 2010 (the years with the greatest amount of emigration) differed, suggesting that social relationships within a population may affect emigration. Emigrants were observed among the Izu Island Chain and in Chiba, Shizuoka, Mie, and Wakayama Prefectures. The greatest distance dolphins emigrated from Mikura Island was 390 km to Tanabe in Wakayama Prefecture. Some individuals were observed to have emigrated to several areas during the period. The most frequent destination was Toshima Island, one of the Izu Islands Chain, where emigrants have been observed to reproduce. Emigrant groups were composed exclusively of individuals from Mikura Island; there were no immigrants to the Mikura Island area during the 20-y period of observation, although six emigrants eventually returned to their original range. Future studies of social relationships and habitat use by emigrants will reveal more about the reasons dolphins leave their habitats.
  • Mai Sakai; Yuki F. Kita; Kazunobu Kogi; Masanori Shinohara; Tadamichi Morisaka; Takashi Shiina; Miho Inoue-Murayama
    SCIENTIFIC REPORTS NATURE PUBLISHING GROUP 6 23902  2045-2322 2016/04 [Refereed]
    Alloparental behaviour and adoption have been reported in many mammals and birds. Such behaviours are energetically costly, and their causes and functions remain unclear. We observed the adoption behaviour of a wild Indo-Pacific bottlenose dolphin (Tursiops aduncus) near Mikura Island, Japan. A calf was seen with its mother on six observation days. Following the mother's death, the calf was observed with a sub-adult female on all 18 observation days from May to September 2012. On three days, the calf was observed swimming with this female in the suckling position and milk was seen leaking from the female's mammary slit. A five-year dataset revealed no significant social or kin relationships between the biological mother and allomother, indicating that kinship and social relationships did not play an important role in the observed adoption.
  • Tadamichi Morisaka; Mai Sakai; Kazunobu Kogi; Hiromitsu Hama
    This paper shows how simple, non-invasive measurement method is important for conserving large animals living underwater. We have studied free-ranging wild Indo-Pacific bottlenose dolphins (Tursiops aduncus) around Mikura Island, Japan for about 15 years. We usually observe dolphin behavior and record acoustics underwater including photo-identification of every dolphins. Despite lots of video data, more basic information such as body size have lacked. In order to measure body size of the animals non-invasively, we used commercial measurement software which can measure the distance between two points on 3D photos by commercial 3D camera. Accuracy evaluation tests using a tape measure between 15 and 250 cm were conducted at the field site (Mikura Island) and the errors were within 5 % of the actual sizes. We successfully measured body size of 33 free-ranging wild dolphins. Mean absolute percentage error of the same individuals in different photos was within 4 % for dolphins. The average size of the adult dolphins was 249.6cm, which was the similar to the average actual size of 4 by-caught dolphins of the population (251.7 cm). We also opportunistically measured green turtles (Chelonia mydas) during our dolphin survey. Mean absolute percentage error of the same individuals in different photos was within 2 % for turtles. The average straight carapace length (SCL) of the 14 turtles was 48.3 cm (37.9 - 67.7 cm), which is much smaller than the adult green turtle length (80 - 111 cm). A simple measurement method is thus important to know the size of the large animals underwater, which indicates animal age and health condition, and are important for conserving these large animals.
  • MORISAKA Tadamichi; SAKAI Mai; SAKAI Mai; KOGI Kazunobu
    東海大学海洋研究所研究報告(Web) (36) 1‐7 (WEB ONLY)  2189-0617 2015/03
  • NARA Shotaro; MIYAKE Maako; TAKAHASHI Shun; INADA Yoshinobu; SAKAI Mai; MORISAKA Tadamichi
    Proceedings. International Conference on Flow Dynamics (CD-ROM) 12th 152‐153  2015
  • Yayoi M Yoshida; Tadamichi Morisaka; Mai Sakai; Mari Iwasaki; Ikuo Wakabayashi; Atsushi Seko; Masahiko Kasamatsu; Tomonari Akamatsu; Shiro Kohshima
    Behavioural processes 108 11 - 9 1872-8308 2014/10 [Refereed]
    Commerson's dolphin (Cephalorhynchus commersonii), one of the smallest dolphin species, has been reported to produce only narrow-band high-frequency (NBHF) clicks and no whistles. To clarify their sound repertoire and examine the function of each type, we analysed the sounds and behaviour of captive Commerson's dolphins in Toba Aquarium, Japan. All recorded sounds were NBHF clicks with peak frequency >110kHz. The recorded click-trains were categorised into four types based on the changing pattern of their Inter-click intervals (ICI): Decreasing type, with continuously decreasing ICI during the last part of the train; Increasing type, with continuously increasing ICI during the last part; Fluctuating type, with fluctuating ICI; and Burst-pulse type, with very short and constant ICI. The frequency of the Decreasing type increased when approaching an object newly introduced to the tank, suggesting that the sound is used for echolocation on approach. The Burst-pulse type suddenly increased in front of the object and was often oriented towards it, suggesting that it was used for echolocation in close proximity to the object. In contrast, the Increasing type was rarely recorded during approach, but increased when a dolphin approached another dolphin. The Increasing and Burst-pulse types also increased when dolphins began social behaviours. These results suggest that some NBHF clicks have functions other than echolocation, such as communication.
  • Yayoi M. Yoshida; Tadamichi Morisaka; Mai Sakai; Mari Iwasaki; Ikuo Wakabayashi; Atsushi Seko; Masahiko Kasamatsu; Tomonari Akamatsu; Shiro Kohshima
    BEHAVIOURAL PROCESSES ELSEVIER SCIENCE BV 108 11 - 19 0376-6357 2014/10 [Refereed]
    Commerson's dolphin (Cepholorhynchus commersonii), one of the smallest dolphin species, has been reported to produce only narrow-band high-frequency (NBHF) clicks and no whistles. To clarify their sound repertoire and examine the function of each type, we analysed the sounds and behaviour of captive Commerson's dolphins in Toba Aquarium, Japan. All recorded sounds were NBHF clicks with peak frequency >110 kHz. The recorded click-trains were categorised into four types based on the changing pattern of their Inter-click intervals (ICI): Decreasing type, with continuously decreasing ICI during the last part of the train; Increasing type, with continuously increasing ICI during the last part; Fluctuating type, with fluctuating ICI; and Burst-pulse type, with very short and constant ICI. The frequency of the Decreasing type increased when approaching an object newly introduced to the tank, suggesting that the sound is used for echolocation on approach. The Burst-pulse type suddenly increased in front of the object and was often oriented towards it, suggesting that it was used for echolocation in close proximity to the object. In contrast, the Increasing type was rarely recorded during approach, but increased when a dolphin approached another dolphin. The Increasing and Burst-pulse types also increased when dolphins began social behaviours. These results suggest that some NBHF clicks have functions other than echolocation, such as communication. (C) 2014 Elsevier B.V. All rights reserved.
  • Morisaka Tadamichi; Sakai Mai; Kogi Kazunobu; Shinke Tomio; Zin Thithi; Hama Hiromitsu
    Memoirs of the Faculty of Engineering Osaka City University GRADUATE SCHOOL OF ENGINEERING OSAKA CITY UNIVERSITY 54 (54) 25 - 29 0078-6659 2013/12
  • Kagari Aoki; Mai Sakai; Patrick J. O. Miller; Fleur Visser; Katsufumi Sato
    BEHAVIOURAL PROCESSES ELSEVIER SCIENCE BV 99 12 - 20 0376-6357 2013/10 [Refereed]
    Synchronous behavior, as a form of social interaction, has been widely reported for odontocete cetaceans observed at the sea surface. However, few studies have quantified synchronous behavior underwater. Using data from an animal-borne data recorder and camera, we described how a pair of deep-diving odontocetes, long-finned pilot whales, coordinated diving behavior. Diving data during overlapping periods of 3.7 h were obtained from two whales within a stable trio. The tagged whales made highly synchronous movements, and their dive durations differed only slightly (3 +/- 3 s). The pair of whales maintained a constant and narrow vertical separation (ca. 3 m) throughout synchronous dives. The overall fluking rate for the same travel speed during synchronous dives was virtually the same as that during asynchronous dives, suggesting that synchronous behavior did not affect locomotion effort. In addition, a possible affiliative behavior was recorded by the animal-borne camera: another individual appeared in 8% of the frames, both with and without body contact to the tagged whale. The primary type of body contact was flipper-to-body. Our study, the first on underwater synchronous behavior and body contact of pilot whales, highlights the utility of using animal-borne devices for enabling new insights into social interactions. (C) 2013 Elsevier B.V. All rights reserved.
  • Mai Sakai; Tadamichi Morisaka; Mari Iwasaki; Yayoi Yoshida; Ikuo Wakabayashi; Atsushi Seko; Masahiko Kasamatsu; Shiro Kohshima
    Journal of Ethology 31 (3) 305 - 313 0289-0771 2013/09 [Refereed]
    Mother-calf interactions and the behaviors of mothers during separation from their calves were examined in four Commerson's dolphin (Cephalorhynchus commersonii) mother-calf pairs. Four infants were observed: 56.8 h over 30 days from birth to 263 days of age, 36.9 h over 20 days from birth to 149 days of age, 10.4 h over 3 days from birth to 2 days of age, and 15.0 h over 3 days from birth to 2 days of age. All four pairs shared common characteristics in the rate and frequencies of mother-calf interactions and the behaviors of mothers during the first week of life. After the first week, individual differences in changes in the frequency of each behavior were observed. The three behaviors considered representative of maternal care (parallel swimming, synchronous breathing, and body-to-body contact) were frequently performed in the first week; thereafter, the frequencies declined. Separate behaviors of mothers were infrequent during the first week and increased with an increase in infants' age. Bumping by infants increased with time, suggesting an increase in soliciting by calves and conflict between mothers and calves. The frequency of flipper-to-body rubbing also changed but in a complex manner, probably because the calves needed to learn how to perform this behavior from their mothers and because initiator and recipient of this behavior can be changed quickly. © 2013 Japan Ethological Society and Springer Japan.
  • Tadamichi Morisaka; Mai Sakai; Kazunobu Kogi; Akane Nakasuji; Kasumi Sakakibara; Yuria Kasanuki; Motoi Yoshioka
    PLOS ONE PUBLIC LIBRARY SCIENCE 8 (8) e72879  1932-6203 2013/08 [Refereed]
    Spontaneous ejaculation, which is defined as the release of seminal fluids without apparent sexual stimulation, has been documented in boreoeutherian mammals. Here we report spontaneous ejaculation in a wild Indo-Pacific bottlenose dolphin (Tursiops aduncus), and present a video of this rare behavior. This is the first report of spontaneous ejaculation by an aquatic mammal, and the first video of this behavior in animals to be published in a scientific journal.
    ヒトと動物の関係学会誌 ヒトと動物の関係学会 (35) 23 - 27 1341-8874 2013/07
    霊長類研究 日本霊長類学会 29 (0) 106 - 106 0912-4047 2013 
     ミナミハンドウイルカ (Tursiops aduncus) の鳴音,特にホイッスルに関する音響的・行動学的な研究は多くなされている.しかし彼らが実際にどのくらいの音圧で鳴音を発しているのかに関しては,水中という環境で研究することの困難さから情報が不足している.音源音圧は鳴音がどのくらいの距離で届くのかといった重要な情報をもたらすため,音声コミュニケーションの研究はもとより,船舶のエンジン音の影響など保全を考える上では必須である.本研究では識別された個体の発する鳴音の音源音圧を推定することを目的とし,そのバリエーションについて考えたい.2012年 9月から 10月に伊豆諸島御蔵島にて新規に開発した水中マイクアレー・ビデオシステムを用いてミナミハンドウイルカと併泳しながらその鳴音を収録した.複数の識別個体からホイッスル音を複数回取得した結果,ホイッスルの音源音圧はイルカの位置や姿勢によって影響を受けていることがわかった.つまり腹部中心が見える位置で録音したホイッスルは,それ以外に比べ音圧が低く,かつ倍音成分が消える.これはホイッスルが噴気孔付近あるいは頭部上方から発せられているためであると考えられる.イルカに対する録音場所も意識しながら録音・解析を行う必要があることがわかった.なお本研究は科研費基盤B (23310166) 『野生イルカ個体群保全のための非侵襲的計測手法の開発』による成果である.
    動物心理学研究 THE JAPANESE SOCIETY FOR ANIMAL PSYCHOLOGY 62 (1) 111-124 (J-STAGE) - 124 0916-8419 2012
  • Mai Sakai; Ding Wang; Kexiong Wang; Songhai Li; Tomonari Akamatsu
    PLOS ONE PUBLIC LIBRARY SCIENCE 6 (12) e28836  1932-6203 2011/12 [Refereed]
    Background: Observing and monitoring the underwater social interactions of cetaceans is challenging. Therefore, previous cetacean studies have monitored these interactions by surface observations. However, because cetaceans spend most of their time underwater, it is important that their underwater behavior is also continuously monitored to better understand their social relationships and social structure. The finless porpoise is small and has no dorsal fin. It is difficult to observe this species in the wild, and little is known of its sociality. Methodology/Principal Findings: The swim depths of 6 free-ranging finless porpoises were simultaneously recorded using a time-synchronized bio-logging system. Synchronous diving was used as an index of association. Two pairs, # 27 (an immature female estimated to be 3.5 years old) and # 32 (an adult male), # 28 (a juvenile male estimated to be 2 years old) and # 29 (an adult male), tended to participate in long periods of synchronized diving more frequently than 13 other possible pairs, indicating that the 4 porpoises chose their social partners. The adult males (# 32, # 29) tended to follow the immature female (# 27) and juvenile male (# 28), respectively. However, during synchronized diving, the role of an initiator often changed within the pair, and their body movements appeared to be non-agonistic, e. g., rubbing of bodies against one another instead of that on one-side, as observed with chasing and escaping behaviors. Conclusions/Significance: The present study employed a time-synchronized bio-logging method to observe the social relationships of free-ranging aquatic animals based on swimming depth. The results suggest that certain individuals form associations even if they are not a mother and calf pair. Long synchronized dives occurred when particular members were reunited, and this suggests that the synchronized dives were not a by-product of opportunistic aggregation.
  • Mai Sakai; Leszek Karczmarski; Tadamichi Morisaka; Meredith Thornton
    Tagging attempts of Heaviside's dolphins (Cephalorhynchus heavisidii) using a remotely-deployed suction-cup tag were performed in Table Bay and St Helena Bay on the southwest coast of South Africa. The observed reactions of dolphins indicate that this tagging approach has negligible impacts on the dolphin behaviour and Heaviside's dolphins might be tagged with suction cup tags without adverse affects.
  • Mai Sakai; Kagari Aoki; Katsufumi Sato; Masao Amano; Robin W. Baird; Daniel L. Webster; Gregory S. Schorr; Nobuyuki Miyazaki
    MAMMAL STUDY MAMMALOGICAL SOC JAPAN 36 (1) 55 - 59 1343-4152 2011/03 [Refereed]
  • Tadamichi Morisaka; Leszek Karczmarski; Tomonari Akamatsu; Mai Sakai; Steve Dawson; Meredith Thornton
    Field recordings of echolocation signals produced by Heaviside's dolphins (Cephalorhynchus heavisidii) were made off the coast of South Africa using a hydrophone array system. The system consisted of three hydrophones and an A-tag (miniature stereo acoustic data-logger). The mean centroid frequency was 125 kHz, with a -3 dB bandwidth of 15 kHz and -10 dB duration of 74 mu s. The mean back-calculated apparent source level was 173 dB re 1 mu Pa(p.-p.). These characteristics are very similar to those found in other Cephalorhynchus species, and such narrow-band high-frequency echolocation clicks appear to be a defining characteristic of the Cephalorhynchus genus. Click bursts with very short inter-click intervals (up to 2 ms) were also recorded, which produced the "cry" sound reported in other Cephalorhynchus species. Since inter-click intervals correlated positively to click duration and negatively to bandwidth, Heaviside's dolphins may adjust their click duration and bandwidth based on detection range. The bimodal distribution of the peak frequency and stable bimodal peaks in spectra of individual click suggest a slight asymmetry in the click production mechanism. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3519401]
  • Acoustic behavior of captive Commerson’s dolphins (Cephalorhynchus commersonii).
    Yoshida Y; Morisaka T; Sakai M; Iwasaki M; Wakabayashi I; Seko A; Kasamatsu M; Fukuzawa H; Akamatsu T; Kohshima S
    The 15th Kyoto University International Sym-posium: Biodiversity, Zoos and Aquariums “The Message from Animals” (2010/09, Nagoya). 2010 [Refereed]
  • Mai Sakai; Tadamichi Morisaka; Kazunobu Kogi; Toru Hishii; Shiro Kohshima
    BEHAVIOURAL PROCESSES ELSEVIER SCIENCE BV 83 (1) 48 - 53 0376-6357 2010/01 [Refereed]
    We quantitatively analysed synchronous breathing for dyads in Indo-Pacific bottlenose dolphins at Mikura Island. Tokyo, Japan. For most cases, we observed dyads swimming in the same direction (97%). in close proximity (i.e., less than 1.5 m) and with their body axes parallel as they breathed synchronously. Moreover, the pairs engaged in identical behaviour before and after the synchronous breathing episodes. These results suggest that the dolphins synchronize their movements, and that synchronous breathing is a component of "pair-swimming", an affiliative social behaviour. Same sex pairs of the same age class frequently engaged in synchronous breathing for adults and subadults, as well as mother-calf and escort-calf pairs. The distance between individuals during synchronous breathing for mother-calf pairs was less than for other pairs. The distance observed between individuals for female pairs was less than for male pairs. The time differences between each exhale for each of the two dolphins involved in synchronous breathing episodes for female pairs were smaller than for male pairs, and time differences for adult pairs were smaller than subadult pairs. These results suggest that age and sex class influenced the characteristics of this behaviour. (C) 2009 Elsevier B.V. All rights reserved.
    Honyurui Kagaku (Mammalian Science) The Mammal Society of Japan 48 (1) 159 - 167 0385-437X 2008/06
  • Mai Sakai; Toru Hishii; Shohei Takeda; Shiro Kohshima
    MARINE MAMMAL SCIENCE BLACKWELL PUBLISHING 22 (4) 966 - 978 0824-0469 2006/10 [Refereed]
    "Flipper rubbing" behavior was quantitatively analyzed in wild Indo-Pacific bottlenose dolphins (Tursiops aduncus) around Mikura Island, Tokyo, Japan. We observed two types of flipper rubbing: (1) F-B rubbing; one dolphin (Rubber) rubbed its flipper over various parts of a partner's (Rubbee) body, and (2) F-F rubbing; both dolphins rubbed each other's anterior flipper edge in alternating shifts. F-B rubbings tended to be initiated by the Rubbee and were terminated by the Rubber. The Rubbee often moved actively its body part that was in contact with the Rubber's flipper, and assumed side-up, upside-down, or other postures while the Rubber remained horizontal in most cases. These facts suggest that the Rubbee engaged in F-B rubbing more actively than the Rubber, and might receive some benefit from the frictional contact during F-B rubbing. Dolphins often switched their roles as Rubber and Rubbee between episodes of flipper rubbing bout. Adults and sub-adults exchanged F-B rubbing and F-F rubbing most often with individuals of the same sex in the same age class. F-B rubbing was frequent in mother-and-calf dyads. Our results suggest that flipper rubbing is an affiliative behavior which could be a quantitative measure of social relationships among individuals of this species in future studies.
  • M Sakai; T Hishii; S Takeda; S Kohshima
    BEHAVIOURAL BRAIN RESEARCH ELSEVIER SCIENCE BV 170 (2) 204 - 210 0166-4328 2006/06 [Refereed]
    To determine whether wild Indo-Pacific bottlenose dolphins (Tursiops aduncus) at Mikura Island, Japan, show asymmetry of eye or flipper use during a social behaviour, we investigated the laterality of flipper-to-body (F-B) rubbing, in which one dolphin ("rubber") rubs the body of another ("rubbee") with its flipper. We analysed 382 episodes of video-recorded F-B rubbings performed by identified individuals (N= 111 rubbers). F-B rubbing was conducted significantly more frequently with the left flipper than with the right flipper. The duration of F-B rubbings was also significantly longer with the left flipper than with the right flipper. Of 20 dolphins, nine individuals showed significant left-side bias as the rubber in this behaviour, whereas no dolphins showed significant right-side bias. The results indicate a population-level left-side bias of the rubber in F-B rubbing. An analysis of the swimming configurations during this behaviour suggests that the asymmetry in F-B rubbing was caused not only by the laterality of the rubber, but by a preference for use of the left eye in both dolphins during this behaviour. Dolphins used the left eye significantly more frequently than the right eye during the inquisitive behaviour, while they showed no significant bias in flipper use during the object-carrying behaviour. These facts also suggest that the asymmetry of F-B rubbing is caused by the preference for using the left eye. Significant left-side bias was observed only in F-B rubbings initiated by the rubbee, in which the rubbee determined its position during this behaviour. This suggests that this behavioural asymmetry was enhanced by the rubbees choosing the left side of the rubber to ensure better and longer rubs. (c) 2006 Elsevier B.V. All rights reserved.
  • Kathleen. M. Dudzinski; Mai Sakai; Keiko Masaki; Kazunobu Kogi; Toru Hishii; Michio Kurimoto
    29 108 - 116 2003 [Refereed]


Books and other publications

Lectures, oral presentations, etc.


  • Fisheries Practical MathematicsFisheries Practical Mathematics Kindai University

Affiliated academic society


Research Themes

  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2027/03 
    Author : 酒井 麻衣
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    Date (from‐to) : 2020/04 -2023/03 
    Author : 酒井 麻衣
    ミナミハンドウイルカにおいては、母親に大きく依存する期間(コドモ期)が出生から3年間以上あり、かなり長い。本研究は「母親や他個体との相互作用・社会関係が、独立した後の社会関係の基盤となり、母親から受けた養育行動が自らが産んだ子への適切な養育行動につながることが、長いコドモ期の適応的意義である。」との仮説を検証する。そのため、25年にわたる個体識別情報のある伊豆諸島御蔵島のミナミハンドウイルカを主な対象とする。オスのコドモ期の社会経験は、独立後の社会関係に影響するかを検討する。また、メスのコドモが母から受けた養育行動の特徴が、母から娘へ受け継がれるかを検証する。そして、繁殖成功した個体とそうでない個体のコドモ期を比較し、コドモ期の社会経験の適応的意義を明らかにする。 R2年度は、1994年から2019年の個体識別データより、出産履歴と母子関係、出産間隔を確認し、繁殖成功例と不成功例のリストアップを行った。2015年から2017年までのデータから採餌行動の分析を行い、また、御蔵島でイルカウォッチングに参加した観光客とガイド業者を対象に,採餌行動に関する情報収集を行った。その結果、昼間の採餌はオスよりメスが多く行っていることが明らかになった。今後、子連れのメスのコドモを同伴した採餌について詳しく分析し母子間の相互作用を確認する。また、母子が並んで泳ぐ時に、母親がコドモよりも尾ビレを多く振っている事例を観察し、野生環境下においてもハクジラの母子において遊泳サポートが起きることを確認した。今後、量的な分析を行う。同じマイルカ科のイロワケイルカの飼育個体において、遊泳サポートが子の生後1か月に頻繁に起き、1か月以降は頻度と効果がともに減少することを明らかにした。野生ミナミハンドウイルカでも同様にコドモの成長による遊泳サポートの頻度や効果の大きさに違いがあるか、分析を行う予定である。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)
    Date (from‐to) : 2016/04 -2019/03 
    Author : SAKAI Mai; SUZUKI Miwa; KOGI Kazunobu; KASHIWAGI Nobuyuki; FURUTA Keisuke; SHIOYU Kazuki; KIRIHATA Tetsuo; RYONO Masahiro; NITTO Hiroshi; KATSUMATA Hiroshi; ARAI Kazutoshi
    In order to clarify the relationship between hormone levels and behavior and stress and psychological happiness of odontocetes, we conducted behavioral observation and measured hormone concentrations in the old skin and serum. The subjects have not gotten a heavy disease during the period. This suggests that these behavioral frequencies and the hormone levels were obtained when dolphins were healthy. In the period when a dolphin rubbed its face against the wall frequently, old skin and serum cortisol concentration were relatively higher. This suggests that this behavior is a sign of stress. The serum β-endorphin concentration tended to be lower when static behavior was longer. This suggests that serum β-endorphin concentration has a relationship with the momentum. Further, the serum cortisol concentration tended be higher when the static time at the middle layer was longer. It suggests that prolonged static behavior in middle layer is a manifestation of stress.
  • 日本学術振興会:科学研究費助成事業 特別研究員奨励費
    Date (from‐to) : 2012 -2014 
    Author : 酒井 麻衣
    「並泳の左右性の分析・接触行動の左偏向の個体発達の分析・母子間の接触行動の左右性の比較・接触行動の個体群間比較」のために、2014年6月、7月、9月に伊豆諸島御蔵島にて野生ミナミハンドウイルカを対象に接触を伴う社会行動・同調行動を水中ビデオ撮影し、データ収集を行った。 「並泳・接触行動の左右性の種間比較」のために、バハマ諸島にて撮影された野生マダライルカの接触行動の分析を行った。2003年から2011年に撮影されたビデオのデータを分析した結果、532例のflipper rubbing(ラビング、胸ビレで相手をこする行動)のうち251例が右ヒレで、281例が左ヒレで行われていた。6例以上のラビングが観察された18個体のうち、2個体において有意に左ヒレを多く使用していた。一方、有意に右ヒレを多く使用する個体はいなかった。一方、flipper touching(タッチ、胸ビレで相手に触る行動)は、119例中、65例が右ヒレ、54例が左ヒレで行われた。6例以上のタッチが観察された1個体においては有意な偏向は見られなかった。 野生マダライルカにおけるラビングの分析結果(集団のうちの一部に左偏向の個体がいること、右偏向の個体がいないこと)は、これまで調べてきた飼育ハンドウイルカ(12頭中6頭が左偏向)、野生ミナミハンドウイルカ(20頭中9頭が左偏向)、飼育マダライルカ(4頭中3頭が左偏向)と同様であり、ラビングにおける左偏向はハクジラ亜目の中で共通している可能性が高まった。また、飼育イロワケイルカでは4頭中4頭すべてが左偏向を示し、ハクジラ亜目の中でも偏向の強さに種差がある可能性が考えられた。
  • 文部科学省:科学研究費補助金(若手研究(B))
    Date (from‐to) : 2011 -2012 
    Author : 酒井 麻衣
    伊豆諸島御蔵島のミナミハンドウイルカは、胸ビレで相手をこする社会行動(ラビング)を、左ヒレで行う傾向がある。この現象が、イルカに共通して現れる行動形式なのか、後天的に獲得された行動が伝播した個体群特有の行動形式(文化)であるのかを明らかにする。そのために、ラビングの左右性の発達・個体群間比較・種間比較を行う。本年度は、御蔵島に約40日間滞在しミナミハンドウイルカの水中行動のビデオデータを収集した。また、能登島に定住する本種8個体に対し予備調査を行い、水中観察可能であることを確認した。篠原正典氏より本種の小笠原個体群の水中ビデオデータを借用し、ラビングの左右性を解析中である。鳥羽水族館のイロワケイルカ4個体(オトナオス1、ワカオス1、オトナメス2)を対象に、ラビングのビデオ撮影及び目視観察を行った。その結果、オトナオスは154例のうち97%、ワカオスは74例中81%で左ヒレを使用することがわかった。オトナメスは12例中42%、11例中82%で左ヒレを使用した。今後、メスのデータを増やす予定である。Kathleen Dudzinski氏より、野外の生簀に蓄養されているハンドウイルカ27個体の水中ビデオデータを借用し、ラビングの左右性を分析した。その結果、左ヒレを使用した例は735例中54%で大きな偏りはなかった。23個体の使用ヒレの偏りを検定したところ、1個体のみ有意に左ヒレを多く使用していたが、有意に右ヒレを多く使用する個体はいなかった。Kathleen Dudzinski氏より、バハマの野生マダライルカの水中ビデオデータを借用し、ラビングの左右性を分析した。その結果、左ヒレを使用した例は499例中53%で大きな偏りはなかった。18個体において使用ヒレの偏りを検定したところ、2個体のみ有意に左ヒレを多く使用していたが、有意に右ヒレを多く使用する個体はいなかった。今年度の解析で、使用ヒレの左右性は、種によって違いがあることが示唆された。
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(若手研究(スタートアップ), 研究活動スタート支援)
    Date (from‐to) : 2008 -2010 
    Author : Mai SAKAI
    Two social behaviors, physical contact and synchrony of odontocetes were studied by using underwater observation of wild dolphins, observation of captive dolphins and biologging system. The results suggest that synchronous breathing is a component of an affiliative social behaviour in Indo-Pacific bottlenose dolphins. The results also show the differences in social contact with flipper of Delphinidae and that of Phocaenidae. Finless porpoises seemed to have undeveloped social structure in previous study, however, our results suggest that they form associations with particular individuals.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(B))
    Date (from‐to) : 2007 -2010 
    Author : Motoi YOSHIOKA; 天野 雅男; Shiro KOHSHIMA; Masao AMANO; Kazutoshi ARAI; Senzo UCHIDA; Seiji OTANI; Kazunobu KOGI; Mai SAKAI; Miki SHIRAKIHARA; Yusuke SEKIGUCHI; Azusa HAYANO; Kyoichi MORI; Tadamichi MORISAKA
    Distribution, genetic relationship among local populations, behavior and reproductive physiology were studied for the conservation of Indo-Pacific bottlenose dolphins around Japan. In Amami Is.area where the species was first reported in Japan, more than 50 dolphins were photo-identified by boat-based surveys. A population was found around Torishima Is., Tokyo for the first time and it is genetically related to Mikura and Ogasawara populations. Frequency of social behaviors of the wild dolphins around Mikura Is.varied with sex and developmental stage. Male reproductive activity was higher in spring to fall seasons.
  • 日本学術振興会:科学研究費助成事業 特別研究員奨励費
    Date (from‐to) : 2005 -2007 
    Author : 森阪 麻衣
    伊豆諸島御蔵島に生息するミナミハンドウイルカを撮影したビデオデータ(2000,01,02年撮影分)から、社会行動の分析を行った。胸ビレで相手をこする行動であるラビングを分析し、受け手がこの行動を求めることが多いことを明らかにした。これは、体表面のケアといった何らかの利益を得ていることを示唆した。同性・同成長段階の個体が最も多くラビングを行った。この結果は、イルカがラビングの相手を選択しており、ラビングには何らかの社会的機能があることを示唆した。得られた知見を4th Young psychologist workshop、日本哺乳類学会自由集会にて発表し、雑誌Marine Mammal Scienceに投稿し、受理された。さらに、ラビング行動は、個体群レベルで左ヒレで行われることが多いことを明らかにし、それは左目で相手を見る傾向が強いことに起因すると考察した。この知見を日本動物心理学会自由集会にて発表した。 1999,02,03年に御蔵島で撮影されたデータから、社会行動の量的分析を行った。また、10月に御蔵島にてフィールド調査を行い、本年度のイルカの接触行動の分析のためのビデオデータを収集した。 7月〜3月に飼育イロワケイルカ新生仔2頭とその母親を観察し、社会行動の発達を分析した。その結果、母子間の接触は、生後直後は体と体の接触の割合が多いが、時間的経過とともに胸ビレと体の接触の割合が多くなることを明らかにした。この知見を日本動物行動学会、2006年度勇魚会シンポジウムにて発表した。 揚子江スナメリ6個体に取り付けた速度・深度・加速度記録計のデータから、社会関係の指標にできると考えられる呼吸同調の分析を行った。その結果、3ペアにおいて有意に多く同調することを明らかにした。この結果は、スナメリが特定の個体と一緒に行動している可能性を示唆した。この知見を、日本水産学会にて発表した。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2005 -2007 
    Author : 森阪 麻衣
    伊豆諸島御蔵島にて、ミナミハンドウイルカのオトナメスが、死児を運搬されている様子を観察・撮影した。このメスは死児を運搬しつつも、1歳児を同伴していた。また、運搬している個体の周囲を十数頭のオスが取り巻いており、音声や泡が通常時に比べて多く記録された。運搬個体は死児を海底に置いて、取巻個体のうちの1個体に噛みつき、また死児を拾い上げて運搬していった。これらの観察から、死児を運搬したのは母親ではない可能性、取巻個体が通常とは異なる状態を認知していた可能性、運搬個体は取巻個体と敵対的な関係にあった可能性が考えられた。ミナミハンドウイルカにおいて、母親以外の個体によるサポートや、オスによる仔殺しが存在する可能性が示唆された。 飼育イロワケイルカの母子2組を観察し、接触行動の発達の分析をした。母子間の身体的接触は次第に減少すること、生後直後は体と体の接触の割合が多いが、時間的経過とともに胸ビレと体の接触の割合が多くなること、また、年長のコドモの方から年少のコドモや母親以外の個体に接近する頻度が増えることを明らかにした。 揚子江スナメリ6個体から得られた遊泳速度・深度・加速度の情報から、水底での採餌行動、呼吸行動、活発/非活発な時間帯、同調遊泳の抽出を試みた。その結果、スナメリば水深約5mで採餌すること、採餌や非活発な時間帯は日和見的であること、オトナオスとワカオスが有意に多く同調遊泳を行っている可能性を示した。 アフリカ大陸南東岸沿岸に生息するコシャチイルカを対象に、群れメンバーの流動性と社会行動の観察を行った。頻繁に群れサイズが変化すること、ラビング(胸ビレで相手をこする行動)、複数個体による同調ジャンプ、追いかけあいなど、様々な社会行動を行うことを明らかにした。また、動物搭載型記録計の取り付けを試みた際のイルカへの影響評価を行い、イルカは異常な反応を見せないことを示した。

Social Contribution Activities

  • イルカの水中社会性ほか
    Date (from-to) : 2017/04/01-2019/03/31
    Role : Lecturer
    Category : Others
    Sponser, Organizer, Publisher  : 川西市
    Event, Program, Title : 生涯学習短期大学水産学科
  • イルカのはなし
    Date (from-to) : 2018/07/13
    Role : Lecturer
    Category : Visiting lecture
    Sponser, Organizer, Publisher  : 御蔵島小学校
    Event, Program, Title : よみきかせスペシャル
  • イルカの水中での暮らし方
    Date (from-to) : 2018/06/09
    Role : Lecturer
    Category : Visiting lecture
    Sponser, Organizer, Publisher  : 近畿大学付属小学校
    Event, Program, Title : 大近小博 5年生向け出張講義
  • イルカのおはなし・ほねのおはなし
    Date (from-to) : 2018/03/26
    Role : Lecturer
    Category : Visiting lecture
    Sponser, Organizer, Publisher  : 近小キッズクラブ
    Event, Program, Title : 出前授業
  • イルカのおはなし
    Date (from-to) : 2018/03/05
    Role : Lecturer
    Category : Visiting lecture
    Sponser, Organizer, Publisher  : こだま保育園
    Event, Program, Title : さいえんす@ほいくえん
  • 生物の不思議講座 ~イルカの不思議~
    Date (from-to) : 2016/12
    Role : Lecturer
    Category : Lecture
    Sponser, Organizer, Publisher  : 宇治市
    Event, Program, Title : 生涯学習センター講座