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Last Updated :2024/10/04

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Master

Affiliation (Master)

  • Faculty of Fisheries Sciences　Marine Bioresource and Environmental Science　Marine Environment and Resource Sensing

Affiliation (Master)

  • Faculty of Fisheries Sciences　Marine Bioresource and Environmental Science　Marine Environment and Resource Sensing

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Profile and Settings

Degree

  • Ph.D.（Hokkaido University）

Profile and Settings

  • Contact Point

    mukaifish.hokudai.ac.jp

  • Name (Japanese)

    Mukai

  • Name (Kana)

    Tohru

  • Name

    200901066628359210

Achievement

Research Interests

  • ターゲットストレングス   計量魚群探知機   音響資源調査   生体密度   魚群探知機   音響反射   プランクトン   生体内音速   水中音響   海洋探査   水中音響技術   ローシー   海洋資源   音速   水中映像   体密度   動物プランクトン   体内通過音速   タイムオブフライト法   超音波散乱特性   海洋生態   カイアシ類   雌雄判別   オキアミ   スルメイカ   可視化   海洋生態系   FMTネット   デッドゾーン   ROV   水産音響   Acoustic Information   Fisheries Acoustics   

Research Areas

  • Environmental science/Agricultural science / Environmental dynamics
  • Life sciences / Aquaculture

Research Experience

  • 2016/04 - Today Hokkaido University Faculty of Fisheries Sciences Professor
  • 2014 Hokkaido University
  • 2005 - 水産科学研究院助教授（海洋生物資源科学部門海洋資源計測学分野） 助教授
  • 2005 - Associate Professor
  • 2000 - 水産科学研究科助教授（環境生物資源科学専攻資源計測学講座） 助教授
  • 2000 - Associate Professor
  • 1995 - 同助教授（水産学部海洋生産システム学科生産システム設計学講座) 助教授
  • 1995 - Associate Professor
  • 1988 - 北海道大学助手（水産学部漁業学科漁業測器学講座） 助手
  • 1988 - Research Associate

Education

  •        - 1986  Hokkaido University  School of Fisheries Sciences
  •        - 1986  Hokkaido University  Faculty of Fisheries

Published Papers

  • Mao Kuroda, Atsuhiko Isobe, Keiichi Uchida, Tadashi Tokai, Toshihide Kitakado, Miho Yoshitake, Yoshinori Miyamoto, Tohru Mukai, Keiri Imai, Kenichi Shimizu, Mitsuharu Yagi, Takahisa Mituhasi, Akimasa Habano
    Science of The Total Environment 925 171421 - 171421 0048-9697 2024/05 [Refereed]
  • NAIZHENG YAN, Tohru Mukai, Kohei Hasegawa, Jun Yamamoto, Yoshiaki Fukuda
    ICES Journal of Marine Science 1054-3139 2023/12/12 [Refereed]
     
    Abstract Measurement of target strength (TS) is important for estimating the abundance of species using fisheries acoustics. However, most researchers have only used a limited number of representative frequencies for acoustic measurements of fish without a swim bladder (bladderless fish). Here, we measured the broadband TS of three bladderless fish species, arabesque greenling (Pleurogrammus azonus), Pacific sand lance (Ammodytes personatus), and pointhead flounder (Cleisthenes pinetorum), using two broadband echosounders. TS measurements were conducted in a seawater tank over frequency ranges of 45–90 and 80–120 kHz using a tether method. Higher TS and directivity were observed at higher frequencies than at lower frequencies for pointhead flounder and arabesque greenling. However, the TS for Pacific sand lance was relatively flat over the measured frequency spectra. Additionally, the TS of pointhead flounder and Pacific sand lance could be expressed as a function of body length and the TS of arabesque greenling could be expressed as a function of body length and frequency, which could be used in fish species discriminations and size estimations.
  • Zhen Lu, TOHRU MUKAI, Yasuzumi Fujimori, Kohji Iida
    Journal of Marine Science and Engineering 2023/11/29 [Refereed]
  • YAN Naizheng, 向井徹, 長谷川浩平, 飯田浩二, 鶴田直剛
    海洋音響学会誌 50 (4) 0916-5835 2023 [Refereed]
  • Yoshiaki FUKUDA, Kohei HASEGAWA, Tohru MUKAI, Tomohito IMAIZUMI
    The Journal of the Marine Acoustics Society of Japan 49 (2) 37 - 45 0916-5835 2022/04/01
  • Bungo Nishizawa, Jumpei Okado, Yoko Mitani, Tomohiro Nakamura, Atsushi Yamaguchi, Tohru Mukai, Yutaka Watanuki
    Fisheries Science 88 (1) 109 - 118 0919-9268 2022/01 [Refereed]
     
    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.
  • Atsuhiko Isobe, Takafumi Azuma, Muhammad Reza Cordova, Andrés Cózar, Francois Galgani, Ryuichi Hagita, La Daana Kanhai, Keiri Imai, Shinsuke Iwasaki, Shin’ichro Kako, Nikolai Kozlovskii, Amy L. Lusher, Sherri A. Mason, Yutaka Michida, Takahisa Mituhasi, Yasuhiro Morii, Tohru Mukai, Anna Popova, Kenichi Shimizu, Tadashi Tokai, Keiichi Uchida, Mitsuharu Yagi, Weiwei Zhang
    Microplastics and Nanoplastics 1 (1) 1 - 16 2021/09 [Refereed]
     
    Abstract A total of 8218 pelagic microplastic samples from the world’s oceans were synthesized to create a dataset composed of raw, calibrated, processed, and gridded data which are made available to the public. The raw microplastic abundance data were obtained by different research projects using surface net tows or continuous seawater intake. Fibrous microplastics were removed from the calibrated dataset. Microplastic abundance which fluctuates due to vertical mixing under different oceanic conditions was standardized. An optimum interpolation method was used to create the gridded data; in total, there were 24.4 trillion pieces (8.2 × 104 ~ 57.8 × 104 tons) of microplastics in the world’s upper oceans.
  • FUKUDA Yoshiaki, MUKAI Tohru, SAWADA Kouichi, MATSUURA Tomohiko
    The Journal of the Marine Acoustics Society of Japan 特定非営利活動法人 海洋音響学会 48 (1) 1 - 14 0916-5835 2021 [Refereed]
     

    We measured the density and sound-speed contrasts of Euphausia pacifica off the coast of Kushiro, Hokkaido from 2010 to 2014. These experiments were carried out in May–June (2010) and September–October (between 2011 to 2014). The density contrast was measured using the density bottle method, and the sound-speed contrast was measured by the time-of-flight method using a T-tube in each year. There were no significant differences in the mean values of the measured density and sound-speed contrasts by year, and the mean density and sound-speed contrasts through all years were 1.043 and 1.040, respectively. We also estimated the dorsal aspect mean target strength (TS) using the distorted-wave Born approximation-based deformed-cylinder model (DWBA model), finding that the relationships between total length (TL) [mm] and the mean TS at each frequency were TS=60.9 log TL−177.2 at 38 kHz, TS=57.2 logTL−163.6 at 70 kHz, TS=52.9 log TL−151.5 at 120 kHz, and TS=44.2 log TL−135.5 at 200 kHz. Since there was less annual variability in the density and sound-speed contrasts during the period examined in the present study, we recommend that the acoustic survey be conducted in September or October.

  • Kohei Hasegawa, Naizheng Yan, Tohru Mukai
    Journal of Marine Science and Technology (Taiwan) 29 (2) 135 - 145 1023-2796 2021 [Refereed]
     
    Measurements of the broadband acoustic backscattering from fish should improve acoustic discrimination between species. The pulse compression processing of broadband systems can be used tomeasure acoustic backscattering with high range resolution and improve signal-to-noise ratio. This may increase opportunities for in situ target strength (TS) measurements, the preferredmethod of collecting TS data. To evaluate the availability of TS spectra for acoustic discrimination, three Simrad EK80 wideband transceivers and split-beam transducers of 70, 120, and 200 kHz were used to collect in situ frequency responses of TS from age-0 juvenile walleye pollock and pointhead flounder, a swim-bladderless flat-fish, distributed in and around Funka Bay, Hokkaido, Japan. The single echoes were extracted frombackscattering data, and the TS spectra of the two species were obtained. However, processing of the broadband acoustic data is under discussion. To ensure the reliability of our data, the TS spectra of standard targets were also calculated. The measured TS spectra of the standard targets were close to the theoretical TS spectra. The individual TS spectra of two species included complex frequency response; however, the mean TS spectrum was relatively stable. The different characteristics of the frequency responses observed for the two species were in good agreement with reported observations. The results available for the acoustic discrimination were similar to the multi-frequencymethod, which uses two or more single frequencies. The rawTS spectra should aid in not only discriminating between species but also estimating the size of the fish.
  • Zhen Lu, Tohru Mukai, Yasuzumi Fujimori, Kohji Iida
    Journal of Marine Science and Technology (Taiwan) 29 (2) 185 - 196 1023-2796 2021 [Refereed]
     
    It is well known that there is bias using different sampling gear, such as a framed midwater trawl (FMT) and a ring net, when measuring the density and length distribution of target species. This limit is characterized by the sampling efficiency of the gear. Acoustic monitoring can be used to determine the sampling efficiencies of this gear, as its noninvasive, wide-range sweeps provide more reliable estimates of absolute abundance of the target species. The density measured by the gear can then be standardized by multiplying the initial density measurement by the derived sampling efficiency. In this study, we compared the estimated densities of the dominant zooplankton in the sound scattering layer (SSL) from acoustic monitoring to the densities of the same species measured using the FMT and ring net. The respective sampling efficiencies of this gear for zooplankton categories was then determined using linear regression models. For small Euphausiidae and Copepoda, the sampling efficiency of ring net was higher than that of FMT. In contrast, the ring net was less effective than FMT for large Euphausiidae. These results highlight that the entering and retention rates of the species depend on the type and characteristics of the survey gear, as well as the size and swimming ability of the target species.
  • Bungo Nishizawa, Nodoka Yamada, Haruka Hayashi, Charlie Wright, Kathy Kuletz, Hiromichi Ueno, Tohru Mukai, Atsushi Yamaguchi, Yutaka Watanuki
    Deep-Sea Research Part II: Topical Studies in Oceanography 181-182 0967-0645 2020/12 [Refereed]
     
    To understand the effect of an unusually early sea-ice retreat in the northern Bering Sea in the spring of 2018 on the marine ecosystem of the northern Bering Sea, we compared at-sea observations of seabird density and acoustic observations of prey (fish and zooplankton) biomass during shipboard surveys around St. Lawrence Island in the summers of 2017 and 2018. Densities of foraging seabirds in 2018 (piscivorous divers: 4.7 birds km−2, planktivorous divers: 5.1, shearwaters: 0.7, surface feeders: 6.6) were lower than those in 2017 (piscivorous divers: 14.7 birds km−2, planktivorous divers: 10.3, shearwaters: 11.9, surface feeders:11.9). Acoustically-determined prey biomass in 2018 (fish: 6.4 m2nmi−2, zooplankton: 2.3) was also lower than in 2017 (fish: 18.4 m2nmi−2, zooplankton: 5.5). Similarly, biomass of macrozooplankton (amphipods, euphausiids, Neocalanus spp. and Calanus marshallae) sampled using bongo nets was smaller in 2018. At scales of 5–30 km, correlations between the seabird density and prey biomass were weaker (−0.2–0.3 of Pearson's r) in 2018 than those in 2017 (0.4–0.9) for all seabirds except planktivorous divers. We suggest that the lack of sea ice, and the resulting lack of ice-edge phytoplankton blooms, may weaken trophic linkages by causing a low biomass of secondary consumers and hence a reduced density of seabirds.
  • Mao Kuroda, Keiichi Uchida, Tadashi Tokai, Yoshinori Miyamoto, Tohru Mukai, Keiri Imai, Kenichi Shimizu, Mitsuharu Yagi, Yuichi Yamanaka, Takahisa Mituhashi
    Marine Pollution Bulletin 161 (Pt A) 111670 - 111670 0025-326X 2020/12 [Refereed]
     
    Marine debris on the seafloor has not been thoroughly investigated, and there is little information compared to other types of marine debris. We conducted bottom trawl surveys to determine the present situation of marine debris on the seafloor in offshore areas around Japan. The survey was conducted in three sea areas with different characteristics. As a result, it was found that the amount of marine debris in submarine canyons (2926.1 items/km2) was higher than on the continental shelf. It was revealed that most marine debris on the seafloor is comprised of plastic products, and that debris on the seafloor retains its condition for a long time (over 30 years) without deterioration. In addition, the type of marine debris is affected by the industries operating in each area. Continuing to investigate marine debris on the seafloor in more areas will contribute to solving the problem of marine debris.
  • Naizheng Yan, Tohru Mukai, Jun Yamamoto, Kohei Hasegawa
    Fisheries Research 105434 - 105434 2020/04 [Refereed][Not invited]
  • Takuya Yamaguchi, Yutaka Isoda, Umihiko Itoh, Tohru Mukai, Naoto Kobayashi
    Oceanography in Japan 日本海洋学会 29 (3) 71 - 90 0916-8362 2020 [Refereed][Not invited]
     

    The Synthetic Aperture Radar (SAR) around the western entrance of the Tsugaru Strait has yielded well-defined images of an internal-wave packet accompanied by two or three surface-streaks (surface convergence within the same water mass), which is active during the stratified season, and whose wavelength is in the order of several hundred meters. Most of the waves in the packet were observed near the topographically shallow parts of the sill. Temporal changes were repeatedly observed in the internal waves confined to the sill using a high-frequency echosounder profiler within one-day in the summer 2017. The acoustic images suggest that a wave packet of extraordinary amplitude (> 150 m) has developed transiently around the downstream side of the sill at the ascending passage flow. This wave packet consists of two or three successive streak bands, with very disturbed sea surface conditions overlying wave troughs, i.e., strong downwelling areas. The dynamics of such waves developing over the sill is studied through a fully nonlinear nonhydrostatic numerical model. The vertical fluid stratification and temporal change of the barotropic passage flow were adjusted to approximate our observation conditions. The results suggest that the wave packet is effectively amplified near the downstream side of the sill, where the Froude number becomes a critical point, because upstream propagating waves on the sill slope stagnate and overlap efficiently. In this dynamical process, however, even if the wave grows to large amplitude, it does not form a well-organized solitary wave, but is rather scattered due to the strong dispersion of waves.

  • 水上 卓哉, 板谷 和彦, 向井 徹, 飯田 浩二
    北海道水産試験場研究報告 = Scientific reports of Hokkaido Fisheries Research Institutes 北海道立総合研究機構水産研究本部 (96) 41 - 52 2185-3290 2019/09
  • Angga Dwinovantyo, Henry M. Manik, Tri Prartono, Susilohadi Susilohadi, Tohru Mukai
    Applied Sciences 9 (9) 1851 - 1851 2019/05/06 [Refereed][Not invited]
  • LU Zhen, 向井徹, 藤森康澄, 飯田浩二
    水産工学 55 (2) 135‐144  0916-7617 2018/11 [Refereed][Not invited]
  • Kazuo Amakasu, Tohru Mukai, Masato Moteki
    Polar Science 12 79 - 87 1873-9652 2017/06 [Refereed][Not invited]
     
    Antarctic krill, Euphausia superba, were observed using a broadband echosounder and their length density distribution was inferred from the echo data through a least square inversion. The observation was conducted in the Indian Ocean sector of the Southern Ocean in January 2014. The transmit signal was a 10-ms linear frequency-modulated signal with a frequency sweep of 20-200 kHz. A large aggregation of Antarctic krill was observed at a sampling station over the continental shelf. The volume-backscattering strengths in the frequency range of 85-187 kHz were determined from the observed echoes. In addition, the signal-to-noise ratio at each frequency was estimated and the measured volume-backscattering strengths were evaluated before inversion for accurate inferences. In this inversion, Antarctic krill were modeled as prolate spheroids and the target strengths were predicted by the distorted-wave Born approximation. The acoustically inferred mean length was in good agreement with the mode length determined by a net sampling performed immediately after the echo sampling. Also, the acoustically inferred length-frequency distribution was in reasonable agreement with the determined one from the net samples. (C) 2017 Elsevier B.V. and NIPR. All rights reserved.
  • HIROSE Miyuki, SHIMURA Tsuyoshi, MUKAI Toru
    Journal of Fisheries Engineering 日本水産工学会 54 (3) 163 - 172 0916-7617 2017 [Refereed][Not invited]
     
    The aim of this study was to compare the effectiveness of acoustic measurements between twofrequencies （38 kHz, 120 kHz） for estimations of the distribution and abundance of 0+ Japanese jackmackerel, Trachurus japonicus, off the Tottori coast in the Sea of Japan. The vessel Tottori Maru No. 1collected acoustic data off the coast of Tottori at frequencies of 38 and 120 kHz （KFC3000）. Samplingwas also conducted using a midwater trawl net and an 80-cm ring net. A sound scattering layer wasfound to overlay the echo of the Japanese jack mackerel when sampled at 38 kHz, presenting an inherentproblem to acoustic studies at this frequency. However, signals from Japanese jack mackerel could beidentified on an echogram at 120 kHz. Also, the density of one individual per m3 （n） of Japanese jackmackerel, determined using the trawl net, was positively correlated with the value of the volumebackscattering strength（ SV） at 120 kHz（Mean SV120 kHz ＝ 10 log n – 58.01（ r ＝ 0.68））. Therefore, it ispossible to estimate the distribution and abundance of 0+ Japanese jack mackerel more accurately using120 kHz data.
  • KIM EUNHO, MUKAI TOHRU, IIDA KOHJI
    NIPPON SUISAN GAKKAISHI 日本水産學會 82 (4) 587 - 600 0021-5392 2016 [Refereed][Not invited]
     

     In and around Funka Bay in southwest Hokkaido, Japan, krill and copepods are the dominant species of zooplankton. In this area, they are important prey for walleye pollock Gadus chalcogrammus and other marine animals. In this study, we examined the possibility of identifying krill and copepods based on differences in volume backscattering strength at different frequencies. Acoustic surveys were conducted in and around Funka Bay in March 2012 aboard the T/S Ushio-maru using a Simrad EK60 quantitative echo sounder. The acoustic data were collected at 38, 120 and 200 kHz. Biological samples were collected by a ring net with vertical towing. To identify the krill and copepods, differences in volume backscattering strength at three frequencies were examined. Krill and copepods showed stronger response at 120 and 200 kHz than at 38 kHz. The results showed that the differences in volume backscattering strength between 120 and 200 kHz (ΔSV200-120 kHz) were −1.5 to 1.3 dB for krill and 2.2-3.7 dB for copepods. Based on these differences between frequencies, we were able to identify krill and copepods.

  • Kyounghoon Lee, Tohru Mukai, Dae-Jae Lee, Kohji Iida
    FISHERIES SCIENCE 80 (1) 1 - 11 0919-9268 2014/01 [Refereed][Not invited]
     
    There are various techniques for identifying fish species, including the multi-frequency method, in situ target strength characteristics, and digital image processing methods. Acoustic Doppler current profilers (ADCPs) are able to determine multiple current fields simultaneously and have been used to observe the swimming speed and behavior patterns of shoals of pelagic fish under natural conditions. In this study, we evaluated a classification method that can be used to determine the swimming velocity of both the sound-scattering layer and pelagic fish shoals using an ADCP (153.6 kHz) and a scientific echosounder (38, 200 kHz). To calculate the actual swimming speed of the fish shoals, the mean swimming velocity vectors of each stratified bin must be compared with the mean surrounding three-dimensional (3D) current velocity vectors. We found the average 3D swimming velocity of the sound-scattering layer to be characterized by a deviation of > 5.3 cm/s from the surrounding current field. The average 3D swimming velocity of Pacific saury Cololabis saira was calculated to be 91.3 cm/s, while that of lanternfish Diaphus theta was 28.1 cm/s. These swimming speeds correspond to 4.19- and 4.26-fold the body length, respectively. Thus, the use of ADCP swimming velocity data can be expected to be a valuable species identification method for various fishes distributed in a given survey area.
  • HIROSE Miyuki, MUKAI Tohru
    The Journal of the Marine Acoustics Society of Japan 特定非営利活動法人 海洋音響学会 41 (1) 1 - 11 0916-5835 2014 [Refereed][Not invited]
     
    Acoustic techniques are commonly used to study the distributions and abundances of fish and zooplankton, because these techniques can survey large areas relatively quickly. Recently, acoustic-scattering techniques such as echosounders have been applied to jellyfish monitoring. Several studies have examined the acoustic-scattering characteristics of Nemopilema nomurai, but the influence of changes in the swimming (swimming angle) of this jellyfish on target strength (TS) has yet to be determined. This information has important implications for estimations of the abundance of jellyfish. In this study, the TS of live jellyfish in a seawater tank was measured to clarify the relationship between TS and swimming angle. Both measured and modeled scattering patterns depended on the swimming angle, revealing that the TS was largest for the head-aspect (incident on the bell of the jellyfish: 0 degree) swimming angle, and 10 dB lower for the intermediate-aspect swimming angle. The reduced target strength (RTS) in the side-aspect angle (range, 20–160º) varied between −60 and −50 dB; there was good agreement between the estimated and measured TS values.
  • AMAKASU KAZUO, MISHIMA YUKA, SASAKURA TOYOKI, MUKAI TOHRU, SAWADA KOUICHI
    海洋音響学会誌 40 (3) 126 - 137 0916-5835 2013/07 [Refereed][Not invited]
  • TAKAHASHI Ryuzo, IIDA Kohji, MUKAI Tohru, NISHIMORI Yasushi
    The Journal of the Marine Acoustics Society of Japan 特定非営利活動法人 海洋音響学会 40 (3) 113 - 125 0916-5835 2013 [Refereed][Not invited]
     
    The horizontal acoustic backscattering strength of a fish school is an important factor for fisheries and for estimation of the size of a fish school using omnidirectional scanning sonar. However, the backscattering strength of a fish school is influenced by their behavior and orientation because the individual fish in the fish school have strong directivity of target strength. This paper discusses a method for estimating the directivity of the backscattering strength of the fish school by analyzing fish school behavior. Sonar data were collected by a purse seine fishing boat equipped with the quantitative scanning sonar FSV-30R in Barents Sea and on the Pacific coast of northern Japan. Swimming speed, swimming direction, volume backscattering strength (SV_SCH), and the target strength of the fish school (NTS) were analyzed for several swimming fish schools. The results showed strong directivity in the backscattering strength at the direction perpendicular to the swimming course; this result is similar to that of the directivity of the target strength. The directivity varied in relation to the distribution of the orientation of the fish, resulting from both the swimming speed and the direction of the fish school. These findings will enable the estimation of fish school abundance more precisely.
  • FUKUDA Yoshiaki, MUKAI Tohru, SAWADA Kouichi, IIDA Kohji
    The Journal of the Marine Acoustics Society of Japan 特定非営利活動法人 海洋音響学会 40 (3) 138 - 148 0916-5835 2013 [Refereed][Not invited]
     
    The target strength (TS) spectrum of a marine organism is a key factor in the target discrimination of that organism. In this study, the side-aspect TS spectrum of Euphausia pacifica was measured as a function of the incident angle of the ensonified wave in a seawater tank using a broadband transducer with a bandwidth of 300–700 kHz. The measurements were compared with the theoretical predictions by the distorted-wave Born approximation-based deformed-cylinder model (DWBA model). The TS pattern measurements were in good agreement with the DWBA model predictions for the main lobe but not with those for the side lobe. The measurements of the relationship between the normalized mean TS spectrum and the total length divided by wavelength ratio were in good agreement with model predictions.
  • KURNIA Muhammad, IIDA Kohji, MUKAI Tohru
    海洋音響学会誌 海洋音響学会 39 (3) 93 - 102 0916-5835 2012/07 [Refereed][Not invited]
     
    We discuss the acoustic characteristics of the three-dimensional target strength (3DTS) of defrosted Japanese Jack mackerel and Chub mackerel. The target strength of fish in the whole aspect was measured in a tank by changing the horizontal incident angle from 0° to 360° by 1° steps and the pitch angle from 0° to 90° by 10° steps. Prior to measurement of TS, morphological parameters including swim bladder size and shape were measured by soft X-ray for theoretical estimation. The theoretical TS of fish were calculated using the prolate-spheroid model based on morphological parameters and were compared with the measured values. Results showed that both the maximum and the minimum TS were proportional to body length, and the directivity of the TS was strongly associated with its orientation. The TS of fish changed significantly with the changing yaw and pitch angle of the fish, but remained fairly constant as the roll angle of the fish changed. The maximum and minimum TS were found at the broadside and end-on aspects of the fish, respectively.
  • FUKUDA YOSHIAKI, MUKAI TOHRU, SAWADA KOUICHI, IIDA KOHJI
    NIPPON SUISAN GAKKAISHI 日本水産學會 78 (3) 388 - 398 0021-5392 2012/05/15 [Refereed][Not invited]
     
      Side-aspect target strengths (TS) of Euphausia pacifica (10.9∼19.6 mm in total length [TL], n=44) were measured as a function of the incident angle of the ensonified wave at 120 kHz and 200 kHz. These measurements were compared with the theoretical predictions by the Distorted-Wave Born Approximation-based deformed-cylinder model (DWBA model). The measurements agreed with the predictions. Dorsal-aspect TSs as a function of the incident angle of the ensonified wave were also predicted by taking the curvature of the body in their swimming condition into account. The relationship between the reduced maximum TS (TScm, max) in dorsal aspect by the DWBA model and the total length to wavelength ratio (TL/λ) was expressed by TScm, max=36.5 log TL/λ−91.4.
  • 広瀬美由紀, HWANG Doojin, 向井徹
    海洋音響学会誌 海洋音響学会 39 (1) 34 - 38 0916-5835 2012/01 [Refereed][Not invited]
  • Yukiko Yamashita, Yasuzumi Fujimori, Toru Mukai, Susumu Shimizu
    Nippon Suisan Gakkaishi (Japanese Edition) 日本水産學會 78 (5) 903 - 912 0021-5392 2012 [Refereed][Not invited]
     
    The Laser Optical Plankton Counter (LOPC) has been used to evaluate abundance structure of micro-organisms like a zooplankton speedy. The sea experiments were conducted at twelve stations near Funka Bay, Hokkaido to examine the performance of the LOPC for in situ measurement of multispecies aggregation of zooplankton. The LOPC was mounted with ring net (80 cm mouth diameter) and towed vertically. Size and volume composition data of LOPC and net samples were compared each other. The particle size composition detected by the LOPC showed similar pattern with wet weight composition of copepods and amphipods in net samples. However, the ranges of equivalent spherical diameter of these species were overlapped. To measure in situ zooplankton community by species using LOPC, the measurement properties of each particle by specie should be identified and discriminated from LOPC data.
  • Muhammad Kurnia, Kohji Iida, Tohru Mukai
    JOURNAL OF MARINE SCIENCE AND TECHNOLOGY-TAIWAN 19 (3) 287 - 293 1023-2796 2011/06 [Refereed][Not invited]
     
    This paper discusses the three-dimensional target strength (3DTS) of fish for a horizontal scanning sonar. Experiments were conducted in a tank using a defrosted Japanese mackerel. Measurements were made by changing the horizontal incident angle of a 50 kHz acoustic beam and the pitch angle of a tethered fish. Following the experiment, morphological characteristics, including the swimbladder size and shape, were measured using soft X-ray and digitized. The theoretical 3DTS was estimated using the prolate spheroid model and compared with the measured 3DTS. Results showed that the TS strongly depended on the fish orientation. The maximum and minimum TS were recorded at the broadside and the head/tail aspect of the fish, respectively. The horizontally averaged TS, which is necessary to estimate fish abundance by horizontal scanning sonar, gradually increased as the pitch angle increased, showing a minimum at 0 degrees and maximum at 90 degrees. The measured horizontally averaged TS was 3-5 dB lower than the theoretically estimated TS. Possible theoretical, biological, and technical reasons are discussed.
  • FUJIMORI YASUZUMI, MUKAI TOHRU, YAMAMOTO JUN
    NIPPON SUISAN GAKKAISHI 日本水産學會 76 (6) 1080 - 1082 0021-5392 2010/11/15 [Refereed][Not invited]
     
    オキアミ採集におけるライトの効果を確認するとともに，その有無が採集個体のサイズ組成に与える影響を調べた。採集には口径 80 cm（NGG32）のリングネットを使用した。ペンネント上部にネット上方に光を照射するようにライトを取りつけ，ライト無し，点灯，閃光（点滅）の 3 条件について夜間に鉛直曳網を行った。ライトをつけた場合では点灯，閃光に関わらず，ライト無しの場合よりも密度は 4～6 倍に増加した。また，採集個体の体長組成はライトの有無で大きく異なり，点灯，閃光に関わらず大型個体の採集量は著しく増加した。
  • Characteristics of Acoustic Scattering according to Pulsation of the Large Jellyfish Nemopilema nomurai
    韓国水産学会誌 43 (5) 551 - 556 2010 [Refereed][Not invited]
  • Miyuki Hirose, Tohru Mukai, Doojin Hwang, Kohji Iida
    ICES JOURNAL OF MARINE SCIENCE 66 (6) 1233 - 1237 1054-3139 2009/07 [Refereed][Not invited]
     
    Reports about jellyfish damaging nets and reducing fish catches are increasing, and data on the abundance and distribution of various jellyfish species are needed to forecast where and when their blooms will happen. Acoustic techniques can be used to obtain this information if the acoustic characteristics of the targets are known. This is a study of acoustic scattering from three jellyfish species: Nemopilema nomurai (order Rhizostomeae), Cyanea nozakii (Semaeostomeae), and Aurelia aurita (Semaeostomeae). Target strength (TS) at 38, 120, and 200 kHz, specific density, and sound speed were measured with live specimens. Specific densities were measured using the displacement-volume-weight and the dual-density methods. The sound speeds were estimated using the time-of-flight method. The reduced TS (RTS), i.e. the TS normalized by bell area, was smaller for N. nomurai (bell diameter range 19-38 cm) than for C. nozakii (bell diameter range 30-40 cm), and the differences in RTS between the species were 17.8, 12.6, and 5.8 dB at 38, 120, and 200 kHz, respectively. The respective sound-speed contrast h and density contrast g were 1.0008 +/- 0.009 (mean +/- s.d.) and 1.004 +/- 0.015 for N. nomurai; 1.038 and 1.073 for one C. nozakii; and 1.0001 +/- 0.025 and 0.989 +/- 0.019 for A. aurita.
  • 石井憲, 安部幸樹, 澤田浩一, 甘糟和男, 向井徹
    超音波Techno 21 (2) 66 - 69 0916-2410 2009/04 [Refereed][Not invited]
  • MATSUKURA RYUICHI, MUKAI TOHRU, ANDO YASUHIRO, IIDA KOHJI, RYUICHI MATSUKURA, TOHRU MUKAI, YASUHIRO ANDO, KOHJI IIDA, Graduate School of Environmental Science Hokkaido University, Faculty of Fisheries Sciences Hokkaido University, Faculty of Fisheries Sciences Hokkaido University, Faculty of Fisheries Sciences Hokkaido University
    NIPPON SUISAN GAKKAISHI 日本水産學會 75 (1) 38 - 44 0021-5392 2009/01/15 [Refereed][Not invited]
     
      The density and sound speed contrasts between Euphausia pacifica and sea water change with the season. In this study, we examined the effect on target strength (TS) and lipid content which is a cause of these changes. Density contrasts increased from spring to summer, but sound speed contrasts decreased. There was a negative correlation between density contrasts and wax esters, which are one of the lipid contents, and a positive correlation between sound speed contrasts and total lipid. The range of variation estimated by the DWBA model using both ratios was narrow. The mean TS of E. pacifica (TL 15 mm) ranged from -105.9 to -105.2 dB at 38 kHz, from -91.3 to -90.5 dB at 120 kHz and from -86.3 to -85.4 dB at 200 kHz.
  • Nobuo Kokubun, Kohji Iida, Tohru Mukai
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 55 (16-17) 1827 - 1836 0967-0645 2008/08 [Refereed][Not invited]
     
    The distributions of murres (Uria spp.) and their prey were examined on board T/S Oshoro maru in the southern part of St. George Island, southeastern Bering Sea during the summers of 2003-2005. Murre distribution was determined by sight-counting survey, and the biomass of fishes and plankton was estimated simultaneously using acoustic measuring. Fish were abundant in intermediate (30-90m) layers around the inner front or the northern edge of Pribilof Canyon, while plankton were abundant in deep (> 90 m) layers around the northern edge of Pribilof Canyon or the shelf-break front. In each year, murres foraged around the inner front or the northern edge of Pribilof Canyon, which had high productivity and abundant fish, as has been revealed previously. Non-linear regression analysis on the vertical distribution of prey and distribution of murres suggested that murres especially targeted on fishes concentrated in intermediate layers below the thermocline. Furthermore, comparison of abundance and distribution of prey revealed that fish abundance was lower and distributed in deeper layers in 2005 than in 2003 and 2004. Low abundance and deep distribution of fish prey may be related to poor breeding success of murres on St. George Island in 2005. (C) 2008 Elsevier Ltd. All rights reserved.
  • LEE KYOUNGHOON, MUKAI TOHRU, LEE DAEJAE, IIDA KOHJI
    Fisheries science : FS 74 (2) 221 - 229 0919-9268 2008/04/01 [Refereed][Not invited]
     
    Acoustic Doppler current profilers (ADCPs) have recently been used to estimate the dynamic characteristics and biomass of sound scattering layers (SSLs) or swimming speed of fish schools and to analyze SSL spatial distribution or various behavior patterns. This paper shows that it is necessary to verify mean volume backscattering strength (MVBS, dB) values acquired from each beam for quantitative analysis of the spatial distribution or the biomass estimates of such specific targets as SSL or a fish school when using an ADCP. In this study, the SSL was selected to be a homogeneous density layer over a large area and two methods were used to verify the MVBS values from each beam of the ADCP. First, a mutual comparison among four beams was conducted after calculating MVBS from the measured echo intensity. Second, the MVBS values were verified using comparison between the calculated MVBS from the 153.6 kHz ADCP and MVBS from three frequencies of a well-calibrated scientific echosounder. Moreover, the dominant scatterers (euphausiids) were collected by a framed midwater trawl. From these samples, biological data were used to identify the different frequency characteristics between two systems, using a distorted-wave Born approximation (DWBA) theoretical backscattering model in order to assess the averaged target strength and target strength TS differences for the three frequencies.
  • FUJIMORI Yasuzumi, YAMASHITA Yukiko, ABE Masayuki, ITAYA Kazuhiko, MUKAI Tohru
    Journal of Fisheries Engineering 日本水産工学会 44 (3) 197 - 204 0916-7617 2008 [Refereed][Not invited]
     
    A trousers-type framed midwater trawl (T-FMT) was developed for the simultaneous sampling of plankton and micronekton, which allows the use of two kinds of mesh sizes at the same time. This paper describes the performance of T-FMT in the survey of plankton and micronekton. In addition, the estimation of size selectivity for these small creatures was conducted by using the SELECT analysis expanded for a sub-sample from the trousers trawl experiment. The experiments for plankton and juvenile walleye pollock were conducted offshore of Usujiri, Hokkaido. Three kinds of codends were prepared: two moji-nets with mesh sizes of 1.7mm (M17) and 3.1mm(M31), respectively, and a plankton mesh with a mesh size of 526μm (PL). A pair of codends, M17 vs. PL and M17 vs. M31, was tested for sampling plankton and juvenile walleye pollock, respectively. Euphausiids dominated the catches of the M17 codend, whereas copepods were dominant in the PL codend. The Iength distribution of euphausiids in the PL codend showed a bimodal shape, whereas of those in the M15 codend showed a unimodal shape. The average L_<50> and S. R. values for the estimated selectivity curve of the M17 codend for euphausiids were 7.8 and 1.0mm, respectively. For the juvenile walleye pollock caught in April (early season after spawning), the length distribution in the M17 and M31 codends showed a deviant shape, i.e. there were no fish smaller than 12mm in length. For the fish caught in June, the length distributions for the M17 and M31 codends showed a unimodal shape, and there was no difference in length distribution between the M17 and M31 codends. Based on these results, it was concluded that the PL and M17 codend pair was suitable for the simultaneous sampling not only of plankton and micronekton but also of juvenile walleye pollock in this area from April to June. In addition, the availability of T-FMT in the study of size selectivity for small creatures was confirmed.
  • Jun Yamamoto, Miyuki Hirose, Tetsuya Ohtani, Katashi Sugimoto, Kazue Hirase, Nobuo Shimamoto, Tsuyoshi Shimura, Natsumi Honda, Yasuzumi Fujimori, Tohru Mukai
    MARINE BIOLOGY 153 (3) 311 - 317 0025-3162 2008/01 [Refereed][Not invited]
     
    The fate of the giant jellyfish Nemopilema nomurai after death was examined in the southwest Sea of Japan. The density of dead jellyfish was greater than that of live animals. The dead animals are heavier than the Japan Sea Proper Water which occurs deeper than 200 m, suggesting that dead jellyfish sink to the sea floor. The sea floor survey, conducted with a towed video tape recorder (VTR) monitoring system between mid September and mid October, observed a total of 138 jellyfish during 28 of 29 operations. The density of carrion ranged between 0.2 and 5.1 individuals/1,000 m(2) (mean +/- SE = 1.1 +/- 0.2). Ophiuroids occurred abundantly at 23 jellyfish carcasses and a sea anemone was observed attached to five carcasses. The VTR surveys confirmed that carrion sinks to the sea floor not only during the winter, the normal end of life for medusae, but also during the fall. A trap survey baited with medusae was also employed, and four different species were sampled with the traps: the snow crab (Chionoecetes opilio), a shrimp (Pandalopsis japonica), the ivory shell (Buccinum striatissimum) and an ophiuroid (Ophiura sarsii). Much of the trap bait remained (49-68% weight-mean = 60.3%) during the 23 h soak-time, and the reduction in weight was greater than that observed by bacterial decomposition, suggesting benthic animals consume dead organisms. The present study indicates that dead N. nomurai sink to the sea floor continuously and were subsequently consumed by benthic scavengers.
  • HIROSE Miyuki, MUKAI Tohru, SHIMURA Tsuyoshi, YAMAMOTO Jun, IIDA Kohji
    The Journal of the Marine Acoustics Society of Japan 海洋音響学会 34 (2) 109 - 118 0916-5835 2007/04 [Refereed][Not invited]
     
    The jellyfish Nemopilema nomurai, which reaches up to 2 m in diameter and 200 kg in weight, has appeared in large numbers in the Sea of Japan during the last several years and has had a negative effect on coastal fisheries in this region. Data on the abundance and distribution of these jellyfish are needed to forecast when and where they will occur in coastal areas. Acoustic techniques are commonly used to study the distribution and abundance of fish and zooplankton because these techniques can survey large areas relatively quickly. Before such surveys can be conducted, the acoustic characteristics of the target species must be known. In this study, the density and speed-of-sound in live jellyfish were measured in order to clarify their acoustic characteristics using a theoretical scattering model. The density of the jellyfish was measured using the dual-density method, while the speed of sound was measured using the time-of-flight method. Their acoustic characteristics were estimated with the distorted-wave Born approximation (DWBA) model using these material properties and the shape of free-swimming jellyfish. The results demonstrate the feasibility of investigating the abundance and distribution of jellyfish using acoustic methods.
  • 山下 由起子, 藤森 康澄, 向井 徹
    Mathematical and physical fisheries science 数理水産科学研究会 5 97 - 104 1348-6802 2007 [Refereed][Not invited]
  • KANG DONHYUG, IIDA KOHJI, MUKAI TOHRU, KIM JONGMAN
    Fish. Sci. 72 (4) 728 - 736 0919-9268 2006/08/01 [Refereed][Not invited]
     
    In this study, density and sound speed contrasts were measured for the Japanese common squid Todarodes pacificus. Target strength (TS) data derived from an acoustic scattering model based on measurements of these two parameters were compared with TS values based on acoustic measurement data to determine whether the measured parameters are reasonable values for theoretical scattering model. Density contrast (g) was measured from the displacement volume and wet weight, while sound speed contrast (h) was measured from the acoustic measurements of travel time (time-of-flight method). The Kirchhoff ray mode model, which represents the squid body as a set of fluid-filled cylinders, was used to calculate theoretical TS. Mean g- and h-values of the squid were 1.029 and 1.041, respectively. Comparison with previous data showed that g was similar, whereas h was relatively high. The difference in the TS between the theoretical model using measured parameters and the acoustic measurement was within 3 dB. Thus, the measured g- and h-values are acceptable for theoretical models of squid.
  • K Iida, R Takahashi, Y Tang, T Mukai, M Sato
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (5B) 4875 - 4881 0021-4922 2006/05 [Refereed][Not invited]
     
    An underwater acoustic camera enclosed in a pressure-resistant case was constructed to observe underwater marine animals. This enabled the measurement of the size, shape, and behavior of living marine animals in the detection range up to 240 cm. The transducer array of the acoustic camera was driven by 3.5 MHz ultrasonic signals, and B-mode acoustic images were obtained. Observations were conducted for captive animals in a water tank and for natural animals in a field. The captive animals, including fish, squid and jellyfish, were observed, and a three-dimensional internal structure of animals was reconstructed using multiple acoustical images. The most important contributors of acoustic scattering were the swimbladder and vertebra of bladdered fish, and the liver and reproductive organs of invertebrate animals. In a field experiment, the shape, size, and swimming behavior of wild animals were observed. The possibilities and limitations of the underwater acoustic camera for fishery applications were discussed.
  • Y Tang, K Iida, T Mukai, Y Nishimori
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (5B) 4868 - 4874 0021-4922 2006/05 [Refereed][Not invited]
     
    Previous studies have resulted in a quantitative omnidirectional sonar (FSV30 research version, Furuno) using 64 multi-beams and a 24 kHz center operating frequency. The practical applications of this sonar are currently being studied with regard to fisheries resource assessment. This paper presents one part of this research, i.e., methods for estimating fish school volume using different sonar scanning modes. To determine its suitability for various purposes, we conducted a simulation to measure scatter aggregation; the simulation was validates by measuring the volume of a balloon filled with seawater. A practical survey was also simulated for spherical scatter aggregation with a 20 m, diameter, and its volume was examined using different scanning modes. Our results indicate that a semicircular cruise mode is more suitable than a circular mode for measuring fish school volume, and that using an anchored instrument scanning mode provides greater accuracy than a cruising scanning mode.
  • Tae-Geon Park, Kohji Iida, Tohru Mukai
    SEA LIONS OF THE WORLD 549 - 560 2006 [Refereed][Not invited]
     
    We investigated the acoustics of Steller sea lion (Eumetopias jubatus) calls in wild individuals hauled out on shore reefs off the west coast of Hokkaido, northern Japan, and in captive sea lions at an aquarium using video camera observations. Steller sea lion calls were classified as "communication," "threat," "wheedling," and "acknowledge" according to associated behaviors. Classified calls were analyzed by means of sonograms for formant frequency (F-1), sound duration (T), and pitch pattern. All sounds emitted by males were lower in formant frequency than those of females, while sounds made by wild animals were lower than those of captive animals. Sounds by males were also longer in duration than those by females, while those made by wild animals were shorter than those by captive ones. Pitch of "communication" calls was a long flat pattern type, "threat" was a short descending type, and "wheedling" was a short ascending type for wild animals and a short wave-like type for the captives. The characteristics of pitch patterns of wild and captive animals suggest that the calls of Steller sea lions are for communication.
  • Kohji Iida, Tae-Geon Park, Tohru Mukai, Shoji Kotani
    SEA LIONS OF THE WORLD 535 - 548 2006 [Refereed][Not invited]
     
    Every winter, hundreds of Steller sea lions (Eumetopias jubatus) visit the coast of Hokkaido, northern Japan. Their foraging behavior destroys fishing gear, which is a serious problem. In order to find a solution that allows the coexistence of both Steller sea lions and fishing activities, attempts have been made to control their behavior using acoustical and optical stimuli. This study examined methods of repelling Steller sea lions from fishery gear using aerial and underwater sounds and flashing lights. In this study, we (1) observed and analyzed the relationship between the calls and the behavior of Steller sea lions; (2) searched for effective stimuli for repelling Steller sea lions; (3) developed a displacing system that generates artificial stimuli to repel Steller sea lions using sounds and lights; and (4) tested the displacing system. Experiments were conducted at a Steller sea lion haul-out located on the west coast of Hokkaido, on the Sea of Japan. Steller sea lions were exposed to acoustical and optical stimuli consisting of repeated intermittent sounds with or without flashing lights. This system was controlled from the edge of a cliff, and the reactions of Steller sea lions were monitored using a video camera and microphone. Most of the Steller sea lions responded to the stimuli by vocalizing toward the source, while moving away and jumping in the water. The most effective stimuli for repelling Steller sea lions were aerial sounds, underwater sounds, and flashing lights in that order.
  • HIROSE MIYUKI, MUKAI TOHRU, HWANG DOOJIN, IIDA KOHJI, MIYUKI HIROSE, TOHRU MUKAI, DOOJIN HWANG, KOHJI IIDA, Graduate School of Fisheries Sciences Hokkaido University, Graduate School of Fisheries Sciences Hokkaido University, College of Fisheries and Ocean Science Yosu National University, Graduate School of Fisheries Sciences Hokkaido University
    NIPPON SUISAN GAKKAISHI 日本水産學會 71 (4) 571 - 577 0021-5392 2005/07/15 [Refereed][Not invited]
     
      The purpose of this study was to estimate the acoustic target strength (TS) of live Nomura's jellyfish Nemopilema nomurai found in the Yellow Sea and the Sea of Japan. The experiments were conducted at Yosu National University, Korea. Seven jellyfish were collected from coastal waters in southern Korea by SCUBA diving and from set-nets. Individual live jellyfish were suspended at the center of a seawater tank (5 m×5 m×5 m) tethered by thin fishing line, and their behavior was monitored by underwater cameras. The TS of each jellyfish was measured at 38 kHz (split-beam system) and 200 kHz (dual-beam system).
       The mean TS values ranged from -79.0 to -47.5 dB at 38 kHz and from -72.2 to -46.0 dB at 200 kHz, and tended to be higher at 200 kHz than at 38 kHz by 1.5 to 10.6 dB. The TS values of similar sized jellyfish were approximately 20 dB lower for those collected by SCUBA diving than those collected in the set-nets. The TS values also varied depending on the form change of the jellyfish.
  • DY Kang, T Mukai, K Iida, DJ Hwang, JG Myoung
    ICES JOURNAL OF MARINE SCIENCE 62 (4) 779 - 789 1054-3139 2005/06 [Refereed][Not invited]
     
    To measure the influence of changes in tilt angle on the acoustic target strength (TS) of the Japanese common squid (Todarodes pacificus), we conducted a series of experiments to estimate TS in relation to tilt angle and swimming angle. Swimming angle was measured in a seawater tank using two infrared, underwater cameras under dark conditions. Ex situ measurements of TS in relation to tilt angle on live specimens using a fishhook and cage method were then conducted at 38 and 120 kHz; mantle length (ML) ranged from 21 to 27 cm (mean 24.75 cm). For the more precise TS measurement with tilt angle, another set of ex situ TS measurements relative to tilt angle was made at 38 and 120 kHz on tethered, anesthetized specimens in seawater. The mean swimming angle was - 17.7 degrees (+/- 12.7 degrees s.d.). The mean TS varied from -48.6 to -44.6 dB and was relatively higher at 120 kHz than at 38 kHz, in the order of 0.7 and 2.5 dB. The empirical relationship between TS (dB) and ML (cm) is given by TS = 20 log(10)(ML) - 75.4 (r = 0.81) at 38 kHz or TS = 20 log(10)(ML) - 73.5 (r = 0.64) at 120 kHz. Based on the tethered method for the anesthetized squid, the mean standardized TS values (b(20)) were found to be highly correlated with the tilt angle, and the resultant fitted equations for b20 were expressed as: b20 = -73.3 + 0.48 X theta + 0.0122 X theta(2) + 0.00016 X theta(3) for 38 kHz and b(20) = -72.6 + 0.53 X theta + 0.0134 X theta(2) + 0.00014 X theta(3) for 120 kHz, where theta is the negative tilt angle in degrees. The mean TS based on the measurements using live squid was higher than that of tethered measurements, i.e., 2.6 dB at 38 kHz and 4.0 dB at 120 kHz. The higher mean TS in the ex situ measurements for the live squid can be explained by the influence of the low tilt angle on the overall TS data. The results can be used to understand the influence of tilt angle on the TS of Todarodes pacificus and thus improve the accuracy of biomass estimates. (c) 2005 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.
  • SADAYASU Kazuhiro, ABE Koki, SAWADA Kouichi, TAKAO Yoshimi, MUKAI Tohru, IIDA Kohji
    The Journal of the Marine Acoustics Society of Japan 特定非営利活動法人 海洋音響学会 32 (1) 30 - 39 0916-5835 2005 [Refereed][Not invited]
     
    Understanding the variability of fish acoustic target strength (TS) potentially improves the accuracy of fisheries acoustic survey. This study examines the effect of fish body bending by swimming activity on fish target strength. Bending shape of fish body and swimbladder were simulated from soft X-ray images of anesthetized walleye pollock. Target strength of bent fish was estimated using a Kirchhoff Ray-Mode model from simulated morphology as a function of fish pitch angle. TS patterns of whole fish and swimbladder did not change near the pitch angle at which maximum TS was obtained. But at the other pitch angle, TS patterns of bent fish differed from that of no bent fish. TS patterns of fish body changed at all the pitch angle. Decrease of maximum TS caused by fish bending was within 0.7 dB. Present study indicates that it is not necessary to take care of fish bending on TS estimation, when fish swimming behaviour is normal except for feeding time that fishes are more active.
  • LEE KYOUNGHOON, MUKAI TOHRU, KANG DONHYUG, IIDA KOHJI
    Fisheries science : FS 70 (6) 1051 - 1060 0919-9268 2004/12/01 [Refereed][Not invited]
     
    An application of the acoustic Doppler current profiler (ADCP, 153.6 kHz) in combination with a scientific echo sounder (EK60, 38 and 200 kHz) was investigated to estimate the density of krill Euphausia pacifica. The acoustic backscattering strength from sound scattering layers was compared with biomass estimates from midwater trawls. Euphausia pacifica was targeted among mixed species populations in the sound scattering layer in the offshore Funka Bay area of Hokkaido, Japan. The frequency characteristics of acoustic backscattering by krill were calculated using a distorted wave Born approximation scattering model at three frequencies. Krill aggregations identified from the EK60 data were extracted as the mean volume backscattering strength difference between two frequencies. They were then used to identify similar aggregations in the ADCP data by matching observation times and depths for the two methods, which were applied simultaneously. Results from the comparison of the mean volume backscattering strength and the density calculated from the ADCP and EK60 showed that ADCP can be used to measure density and spatial-temporal distribution of krill aggregations. Current speed and direction at the study site were found to be 16.1 cm/s and 187.00, respectively, and krill speed and direction (including the current component) were found to be 19.8 cm/s and 172.20, respectively Based on the ADCP data, the net speed and direction of the krill aggregations were found to be 5.9 cm/s and 128.00, respectively.
  • KANG DONHYUG, SADAYASU KAZUHIRO, MUKAI TOHRU, IIDA KOHJI, HWANG DOOJIN, SAWADA KOUICHI, MIYASHITA KAZUSHI
    Fish. Sci. 70 (5) 819 - 828 0919-9268 2004/10/01 [Refereed][Not invited]
     
    Black porgy are hatched and released in marine ranching areas in Japan, Korea and Taiwan to maintain fisheries resources in coastal areas. If acoustic methods are used for field surveys, target strength (TS) information on the species is needed to convert acoustic data to biomass density. Target strength of black porgy (Acanthopagrus schlegeli) 15.5 - 32.9 cm fork length (nine individuals) was measured at 38 and 120 kHz (split beam) by ex situ measurements (cage and fishhook methods) of living fish, a tethered method with shock-frozen fish, and an acoustic scattering model, the Kirchhoff ray mode (KRM) model based on fish morphology. The ex situ TS-to-fork length (FL, cm) relationships were TS38kHz = 20log(10)FL - 64.6 (r = 0.77) and TS120kHz, = 20log10FL - 65.2 (r = 0.70). The values for the KRM model were TS38kHz = 20log(10)FL - 64.8 (r = 0.88) and TS120kHz = 20log(10)FL - 65.4 (r = 0.80). The agreement between the ex situ measurements and the KRM model for the mean TS was very good. In contrast, the results for the tethered method (TS38kHz, = 20log10FL - 69.3 [r = 0.42]) differed markedly from the other two methods, perhaps because of the effects of the shock-freezing procedure in air. The results of the ex situ measurements and scattering model provide basic information for studying TS and conducting acoustic surveys of black porgy, even though the tethered method must be modified.
  • YAMAMOTO Jun, MUKAI Tohru, IWAMORI Toshihiro, KIMURA Osamu, SAKURAI Yasunori
    Journal of the Japan Society for Marine Surveys and Technology 海洋調査技術学会 16 (2) 25 - 30 0915-2997 2004/09/30 [Refereed][Not invited]
     
    A remotely operated vehicle (ROV) was used to observe a sound scattering layer (SSL) identified using a quantitative echo sounder near the mouth of Funka Bay, Hokkaido. The SSL was seen in a high frequency (100kHz) echogram to occur within 5 m of the sea floor. Video images taken by the ROV showed a dense school of krill swimming rapidly and continuously within the SSL. Furthermore, several walleye pollock were observed to approach the ROV at depths where relatively strong echoes appeared in a low frequency (25kHz) echogram. The density and size of the krill and walleye pollock were not determined, however, it is clear that ROVs are useful for observing the SSL and can provide valuable information about the biomass of marine resources more accurately.
  • KUSUMOTO Nami, ANDO Yasuhiro, MATSUKURA Ryuichi, MUKAI Tohru
    Journal of Oleo Science 公益社団法人 日本油化学会 53 (1) 45 - 51 1347-3352 2004/01/01 [Refereed][Not invited]
     
    This paper reports the total lipid content, lipid class composition, and fatty acid composition of the krill Euphausia pacifica collected in the northwestern Pacific Ocean near Funka Bay, Hokkaido, Japan. The krill were caught in spring, summer, and winter in three consecutive years, 2000-2002. Lipid content of the E. pacifica samples was ranged from 5.1 to 11.6% on the basis of dry weight. Major lipid classes determined for the samples of 2002 were triacylglycerols (TAG) (3.4-27.3%), free fatty acids (FFA) (6.9-22.2%), sterols (5.4-12.9%), phosphatidylethanolamines (PE) (3.4-17.5%), and phosphatidylcholines (PC) (36.2-53.8%). All of the samples subjected to fatty acid analysis were high in 16:0 (19.0-24.5% of total fatty acids), 18:1n-9 (7.5-10.0%), 18:1n-7 (6.3-8.1%), 20:5n-3 (IPA) (15.3-24.7%), and 22:6n-3 (DHA) (8.4-20.7%). The lipids of E. pacifica were found to be generally rich in PC and in IPA and DHA. Lipid content and proportion of TAG were higher in the spring samples than in the summer samples. The summer samples were higher in the concentration of DHA in total fatty acids.
  • KUSUMOTO N, Ando Yasuhiro, Matsukura Ryuichi, Mukai Tohru
    Bulletin of fisheries sciences, Hokkaido University 北海道大学大学院水産科学研究科 54 (3) 73 - 77 1346-1842 2003/12 [Not refereed][Not invited]
  • HONDA SATOSHI, SUZUKI CHIHIRO, MUKAI TOHRU, IIDA KOHJI
    NIPPON SUISAN GAKKAISHI 公益社団法人 日本水産学会 69 (4) 558 - 567 0021-5392 2003/07/15 [Refereed][Not invited]
     
    The attenuation of acoustic energy due to the effects of sailing were measured on the RV Kaiyo-maru No.3 by integrating the area backscattering strength (Sa) of the sea bottom. The attenuation of the bottom Sa appeared with the increase of the ship speed. In particular, the attenuation was apparent under the head sea condition of sailing ; maximum attenuation of 1.3 dB was attained at 38 kHz, and 0.7 dB at 12 kHz. On the other hand no clear attenuation occurred under the conditions of a following sea. Under the head sea condition of sailing, the attenuation by sailing occurred at a slower sailing speed than the appearance of a missing echo or apparent attenuation shown on the echogram. That is, the attenuation by sailing exerted an influence upon the acoustic data without the operator being aware of it. When planning an acoustic survey by the RV Kaiyo-maru No.3, or even in a survey field, setting the sailing direction in a following sea will prevent underestimation of the acoustic biomass index caused by the acoustic attenuation due to the effects of sailing.
  • 本間隆之, 高柳志朗, 坂口健司, 三宅博哉, 和田昭彦, 武藤卓志, 飯田浩二, 向井徹, 中野健一
    北海道立中央水産試験場事業報告書 2001 149 - 150 2002/12 [Not refereed][Not invited]
  • Use of Geographical Parameters of Fish School in the Estimation of Fish School Abundance Using Scanning Sonar
    Bull. Korean Soc. Fish. Tech. 38 197 - 291 2002 [Not refereed][Not invited]
  • Observation of Juvenile Sourthern Bluefin Tuna (Thunnus maccoyi C.) School Response to the Approaching Vesel Using Scanning Sonar
    J.Fish.Sci.Tech. 5 206 - 211 2002 [Not refereed][Not invited]
  • The Application of Image Processing Technology for the Analysis of Fish School Behavior: Evaluation of Fish School Behavior Responce to the Approaching Vessel Using Scanning Sonar
    J.Fish.Sci.Tech. 5 212 - 218 2002 [Not refereed][Not invited]
  • MIYAKE HIROYA, ISHIDA RYOTARO, MUTO TAKASHI, ABE KOKI, MUKAI TOORU, IIDA KOJI
    北海道立水産試験場研究報告 北海道立水産試験場 (59) 11 - 24 0914-6830 2001/03/30 [Not refereed][Not invited]
     
    1996～1998年の各年10月に北海道西岸日本海で，計量魚群探知機によりスケトウダラの空間分布を調べ，その現存量を推定した。スケトウダラは各年とも南側海域の大陸棚斜面域に多かった。分布深度は，沿岸域で，昼間380～440m，夜間340～460m，沖合域で，昼間420～580m，夜間340～500mであった。分布様式は昼夜で異なり，夜間には水平的，鉛直的に分散する傾向が見られ，特に上方への移動が顕著であった。これらから音響調査には夜間が適していると考えられた。昼夜込みのデータを用いて推定した現存量は，1996年が23万トン，1998年が45万トンであった。しかし，昼夜毎の推定値の比較から，これらは20%程度過小評価していると考えられた。また，空間サンプリング誤差は10%程度であったので，現存量の推定誤差の合計は約28%と推定された。
  • Verification of diurnal change of target strength of walleye pollock. - An effect of resolution volume -
    Koki Abe, Satoshi Honda, Tatsuki Oshima, Kazushi Miyashita, Kohji Iida, Tohru Mukai
    Proceedings of the ACOUSTGEAR2000 1 48 - 54 2001 [Refereed][Not invited]
  • Observation of juvenile southern bluefin tuna (Thunnus maccoyii C.) school in response to the approaching vessel using a scanning sonar
    Yoo-Won Lee, Kazushi Miyashita, Tsutomu Nishida, Sei-ichiro Harada, Tohru Mukai, Kohji Iida
    Proceedings of the ACOUSTGEAR2000 1 108 - 112 2001 [Refereed][Not invited]
  • LEE Yoo-won, MUKAI Tohru, IIDA Kohji
    NIPPON SUISAN GAKKAISHI 日本水産學會 66 (5) 825 - 832 0021-5392 2000/09/15 [Refereed][Not invited]
     
    The response behavior of a fish school to an approaching vessel was observed using a scanning sonar. The evaluation method using six parameters which signify characteristics of school shape and behavior was proposed. In the two trial survey cruises, fifteen fish schools were analyzed, and among them five schools were identified for their changing shape, swimming direction, and swimming speed. Moreover, by continuously tracing fish schools on the sonar display, these fish schools were seen to exhibit an apparent change of school shape and behavior. Therefore, the evaluation method of fish school behavior using six characteristic parameters indicating fish school shape and behavior is useful.
  • MIKAMI Hisayuki, MUKAI Tohru, IIDA Kohji
    NIPPON SUISAN GAKKAISHI 日本水産學會 66 (4) 682 - 689 0021-5392 2000/07/15 [Refereed][Not invited]
     
    In recent years, acoustic technology has been extensively used for estimating krill abundance. This acoustic assessment is required for precise estimate of target strength (TS) of a krill. However, prediction of the target strength from the theoretical scattering models is generally dependent on the swimming angle, the density and sound speed contrasts between krill and seawater. In these parameters, the density contrasts and sound speed contrasts are known to change during the year. In this study, the seasonal variations of the specific density and sound speed contrasts of Euphausia pacifica are presented. The specific densities of E. pacifica were measured in a series of saline or glycerol solutions of different densities. The measurements of the sound speed were performed using T-shaped velocimeter with two transducers mounted at the ends of the horizontal tube. The specific densities of E. pacifica changed about 1% with season. The sound speed contrasts also varied about 3% with season. These seasonal changes yielded difference about 5dB in target strength of E. pacifica calculated from a straight cylinder model.
  • IIDA K.
    Proceedings of the 3rd JSPS International Seminar on Sustainable Fishing Technology in Asia towards the 21st Century 214 - 219 2000 [Not refereed][Not invited]
  • ABE Koki, IIDA Kohji, MUKAI Tohru
    NIPPON SUISAN GAKKAISHI 日本水産學會 65 (2) 252 - 259 0021-5392 1999/03/15 [Refereed][Not invited]
     
    The influence of diurnal vertical migrations of walleye pollock on acoustic survey was investigated. The experiments were conducted at Musashi-Tai and off Shakotan Peninsula in northern Japan Sea using a split beam type scientific echo-sounder SIMRAD EK500. Area backscattering coefficient (SA) and target strength (TS) of walleye pollock were measured in the daytime and in the nighttime. Results showed that the SA in the nighttime was three times higher than SA in the daytime in Musashi-Tai. Also the SA in the nighttime was 1.4 times higher than that in the daytime off Shakotan Peninsula. However, there were no significant differences of in situ TS of walleye pollock between day and night in both areas. Since the remarkable vertical migration of walleye pollock in bottom layer was observed in echograms, it is concluded that the diurnal changes of SA were caused by underestimation due to the hiding of the shoal of walleye pollock in acoustic deadzone near the bottom in the daytime.
  • IIDA Kohji, MUKAI Tohru, MORI Hideki
    NIPPON SUISAN GAKKAISHI 日本水産學會 65 (1) 66 - 72 0021-5392 1999/01/15 [Refereed][Not invited]
     
    Acoustic volume backscattering strength (SV) was measured at frequencies of 38, 50, 120 kHz from zooplankton and juvenile fish in the sound scattering layer (SSL) off northwestern Hokkaido. Organisms in the SSL were collected by beam trawl hauls at eight stations where the acoustic measurements were recorded. Euphausiids, copepods and juvenile walleye pollock were abundant organisms in the SSL. The composition of the species of sampled organisms was different at each station. When euphausiids were dominant in the SSL, the SV increased with acoustic frequencies. When juvenile walleye pollock were dominant, the SV showed a higher value than that in the above situation, and it was less changed by acoustic frequencies. These differences were explained by the frequency characteristics of acoustic backscattering of euphausiids and walleye pollock. The target strengths of euphausiids and juvenile walleye pollock were estimated by the multiple linear regression model. The results showed that there were some differences between estimated TS and theoretical TS, and the possibility of estimating TS using the multiple linear regression model.
  • IIDA Kohji, MUKAI Tohru, HWANG Doo-Jin
    Fisheries Science Japanese Society of Fisheries Science 64 (6) 929 - 934 0919-9268 1998/12/01 [Not refereed][Not invited]
     
    Acoustic target strengths of captive juvenile fishes of three species were measured at four frequencies using fish cage method. Measurements were conducted on a barge constructed at a fishing port for the experiments, Measured fish were sea smelt Hypomesus pretiosus japonicus (Brevoort), goldeye rockfish Sebastes inermis (Cuvier), and purple puffer Takifugu porphyreus (Temminck et Schlegel). They were caught with a miniature purse seine and maintained in fish breeding tanks before the experiments. Their body lengths ranged from 30 to 65 mm. Each species was classified into three size classes. Specimens were maintained in a cubical cage of 0.5 m each side made of lace cloth during measurement. The echo signals from encaged fish at 25, 50, 100, and 200 kHz were recorded with a data recorder. Echo signals were later digitized and processed by squared integration to calculate the target strengths. The results show that, (1) The backscattering strength of encaged juveniles indicates a linear density dependence for most sample sets, (2) The normalized target strengths TScm of juveniles ranged from -66 to -55 dB, which is maximum 10 dB higher than that of adults, (3) Target strength changed by the frequency, that is, the TScm for L/lambda less than or equal to 2 was roughly 10 dB higher than the TScm for L/lambda greater than or equal to 2.
  • MIYAKE HIROYA, KANETA TOMONORI, MIZUNO MASAMI, YOSHIDA HIDEO, ISHIDA RYOTARO, NATSUME MASASHI, IIDA KOJI, MUKAI TOORU
    水産海洋研究 62 (1) 30 - 32 0916-1562 1998/02 [Not refereed][Not invited]
  • MIYAKE Hiroya, KANETA Tomonori, MIZUNO Masami, YOSHIDA Hideo, ISHIDA Ryotaro, NATSUME Masashi, IIDA Kohji, MUKAI Tohru
    Bulletin of the Japanese Society of Fisheries Oceanography 水産海洋学会 62 (1) 30 - 32 0388-9149 1998/02/01 [Not refereed][Not invited]
  • IIDA Kohji, MUKAI Tohru, HORIUCHI Noritaka
    The Journal of the Marine Acoustics Society of Japan 特定非営利活動法人 海洋音響学会 25 (4) 240 - 249 0916-5835 1998 [Not refereed][Not invited]
     
    Sonar images obtained from a scanning acoustical beam are usually two-dimensional sectional images. However, since the sectional images can be easily obtained as an observation vessel moves forward, we can reconstruct three-dimensional images of underwater objects by analyzing stacked two-dimensional sectional images.
    The echo survey was conducted in Funka Bay aboard the R/V Ushio Maru, which is equipped with a 180-degrees sector scanning sonar (model KCH 1827, Kaijo Co. LTD). The sonar beam was directed downward perpendicularly to the ship's course. Vertical sectional sonar images were digitized every 1.5 seconds while the vessel was cruising at 10 knots. The stacked sectional images were analyzed to determine the spatial distribution and shape of fish schools using the three-dimensional image processing software SLICER.
    The distribution of fish schools was displayed by simultaneous expression of both horizontal and vertical projections. This expression method enabled us to observe fish avoidance from vessel, which can not be observed using ordinary vertical echo sounders.
    The reconstructed solid shape of fish schools by volume rendering could be observed by changing the visual point freely. This allowed to determine scale, features, and swimming direction of the fish schools. Three-dimensional display of sector scanning sonar images is a useful tool not only for a commercial fishing, but also for scientific surveys of fish resources and underwater drifters.
  • Three Dimensional Visualization of Fish Schools using Sector Scanning Sonar
    International Archives of Photogrammetry and Remote Sensing 32 729 - 734 1998 [Not refereed][Not invited]
  • IIDA Kohji, MUKAI Tohru, HORIUCHI Noritaka
    The Journal of the Marine Acoustics Society of Japan 特定非営利活動法人 海洋音響学会 25 (4) 240 - 249 0916-5835 1998 [Not refereed][Not invited]
     
    Sonar images obtained from a scanning acoustical beam are usually two-dimensional sectional images. However, since the sectional images can be easily obtained as an observation vessel moves forward, we can reconstruct three-dimensional images of underwater objects by analyzing stacked two-dimensional sectional images.<BR>The echo survey was conducted in Funka Bay aboard the R/V Ushio Maru, which is equipped with a 180-degrees sector scanning sonar (model KCH 1827, Kaijo Co. LTD). The sonar beam was directed downward perpendicularly to the ship's course. Vertical sectional sonar images were digitized every 1.5 seconds while the vessel was cruising at 10 knots. The stacked sectional images were analyzed to determine the spatial distribution and shape of fish schools using the three-dimensional image processing software SLICER.<BR>The distribution of fish schools was displayed by simultaneous expression of both horizontal and vertical projections. This expression method enabled us to observe fish avoidance from vessel, which can not be observed using ordinary vertical echo sounders.<BR>The reconstructed solid shape of fish schools by volume rendering could be observed by changing the visual point freely. This allowed to determine scale, features, and swimming direction of the fish schools. Three-dimensional display of sector scanning sonar images is a useful tool not only for a commercial fishing, but also for scientific surveys of fish resources and underwater drifters.
  • Hwang Doojin, Iida Kohji, Mukai Tohru
    The Journal of the Marine Acoustics Society of Japan 特定非営利活動法人 海洋音響学会 24 (3) 165 - 175 0916-5835 1997 [Not refereed][Not invited]
     
    The bottom detection is very important for defining an integration layer with the bottom as a reference basis during acoustic survey of demersal fish.
    Therefore, we have considered theoretically elements which form bottom echoes, and have devised a stable bottom detection method namely maximum differential voltage method, which was not influenced by variable levels and waveform transformation. The method has been shown to be effective using in-situ bottom echo waveforms and computer simulation data.
    A comparison between near-botton SV profiles acquired in Funka Bay Hokkaido of Japan and East China Sea, with the threshold method and maximum differential voltage method, shows that the SV obtained with the maximum differential voltage method is 4-6 dB higher within 2m from the bottom.
  • MUKAI T
    ICES C. M. 7 1 - 15 1997 [Not refereed][Not invited]
  • MIYASHITA Kazushi, AOKI Ichiro, IIDA Koji, MUKAI Tohru, HWANG Doojin
    Bull. Jpn. Soc. Fish. Oceanogr. 水産海洋学会 60 (2) 130 - 135 0388-9149 1996/05/25 [Not refereed][Not invited]
  • T Mukai, K Iida
    ICES JOURNAL OF MARINE SCIENCE 53 (2) 245 - 248 1054-3139 1996/04 [Not refereed][Not invited]
     
    The target strength (TS) of fish varies with a number of factors, especially the presence or absence of a swimbladder. This study investigated the effect of the swimbladder on the TS of live kokanee (Oncorhynchus nerka) in relation to depth. Experiments were conducted at Lake Kuttara, Hokkaido, Japan, which is abundant with kokanee. Fish samples were caught with a fishing net. The live fish were suspended on the sound beam axis, and tilted from -50 degrees (head-down aspect) to +50 degrees (head-up aspect). The dorsal aspect TS functions were measured al 50 kHz. Measurements were performed when the fish were forced to change depth rapidly. The TS values were measured as a function of tilt angle and depth, and the maximum dorsal aspect TS (TSmax) values and the averaged dorsal aspect TS (TSavg) values were calculated and compared. TSavg values were calculated with respect to fish tilt-angle distribution, which was assumed to have a mean value of -5 degrees and a standard deviation of 15 degrees. Both TSmax and TSavg decreased with depth in accordance with Boyle's law, i.e. a reduction rate of 6.7 dB per 10 atm was observed. (C) 1996 International Council for the Exploration of the Sea
  • K Iida, T Mukai, DJ Hwang
    ICES JOURNAL OF MARINE SCIENCE 53 (2) 507 - 512 1054-3139 1996/04 [Not refereed][Not invited]
     
    Hydroacoustic sampling in the ocean is a useful technique for studying the biomass and structure of the distribution of marine organisms, including zooplankton. Acoustical and biological sampling of zooplankton in the sound-scattering layer (SSL) off the east coast of Oshima Peninsula, northern Japan has been conducted during the last 10 years to obtain the scale factor for converting the backscattering strength to biological density. The volume backscattering strength (SV) was measured at 25, 50, 100, and 200 kHz, while an IKMT (Isaacs-Kidd Midwater Trawl) and a Norpac (North Pacific standard net) were used to sample the biological organisms in the SSL. During drifting observation at dusk, the maximum speed of the upward migration of the SSL toward the surface was 3 m min(-1), and the SV changed over a range from -80 dB to -50 dB. Vertical lows of the Norpac indicated that euphausiids were the major zooplankton species of the migrating SSL. For quantitative analysis, the IKMT was towed horizontally about one hundred times, and the calculated density of zooplankton showed a maximum of 10g m(-3). We assumed that the acoustic reflectivity of the individual plankton was related to the size of the plankton squared, and that the acoustic backscattering strength of biomass was proportional to the distribution density, Results of regression analysis showed a linear relationship between the log of zooplankton density rho (mg m(-3)) and the acoustic volume backscattering strength SV (dB), with correlation coefficients greater than 0.5 at all frequencies. (C) 1996 international Council for the Exploration of the Sea.
  • K Iida, T Mukai, Y Aoki, T Hayakawa
    ACOUSTICAL IMAGING, VOL 22 22 583 - 588 1996 [Not refereed][Not invited]
  • PARK Yong-seok, IIDA Kohji, MUKAI Tohru, SAKURAI Yasunori
    NIPPON SUISAN GAKKAISHI 日本水産學會 61 (2) 159 - 163 0021-5392 1995/03/15 [Not refereed][Not invited]
     
    The auditory threshold levels of walleye pollock Theragra chalcogramma (Pallas) were measured in order to determine the optimum conditions for marine ranching utilizing underwater sound. The auditory characteristics of walleye pollock were determined by heart beat conditioning using 8 frequencies of pure tone stimuli from 60 to 1, 000Hz coupled with an electric shock. Pure tone conditioning stimuli were presented to the fish for 5 seconds with a 0.1 second 12V DC electric shock applied 3 seconds after the start of the sound projection. The positive response to the pure tone stimulus of the conditioned fish consisted of an inhibition of one or more heartbeats.
    Results show that tested walleye pollock are sensitive to pure tones in the frequency range from 60 to 1kHz, with greatest sensitivity in the range from 120 to 200Hz. At the most sensitive frequencies, the mean thresholds were between 97.7 and 100.2dB (re 1μPa) under a background noise level between 55 and 75dB (re 1μPa/√Hz). Hearing ability declined gradually with increasing frequency above 400Hz. The upper limit of audible frequency is believed to be about 1kHz.
  • PARK Yong-seok, SAKURAI Yasunori, IIDA Kohji, MUKAI Tohru
    NIPPON SUISAN GAKKAISHI 日本水産学会 61 (2) 243 - 244 0021-5392 1995/03/15 [Not refereed][Not invited]
  • HWANG Doojin, IIDA Kohji, MUKAI Tohru
    NIPPON SUISAN GAKKAISHI 日本水産學會 61 (1) 43 - 50 0021-5392 1995/01/25 [Not refereed][Not invited]
     
    This paper discusses methods for the stable bottom detection and the optimum bottom offset which enable to separate the fish echoes from the bottom echoes with echo integration of demersal fish.
    In preprocessing of the echo signal, the bottom detection has to be done stably against the fluctuation of echo level and the bottom offset has to be set to a minimum height such that near bottom fish echoes are included.
    Two methods of bottom detection, namely echo level threshold method and maximum echo slope method were compared and analyzed. The echo level method works well if the ideal threshold level was given but it sometimes misses the bottom because of the fluctuation of the echo. Another method to detect the bottom which uses maximum echo slope indicates the simple and stable bottom detection.
    In addition, the bottom offset has to be set near to the bottom but not to include the bottom echo. Optimum bottom offset should be set a few samples before the detected bottom echo which relates the beginning of pulse shape and acoustic beam pattern to the bottom feature.
  • IIDA Kohji, MUKAI Tohru, HWANG Doojin, HAYAKAWA Tomoko, MATSUYAMA Yukihiro
    NIPPON SUISAN GAKKAISHI 日本水産學會 61 (1) 27 - 34 0021-5392 1995/01/25 [Refereed][Not invited]
     
    The distribution and behavior of so-called spawing walleye pollock Theragra chalcogramma around Funka Bay were investigated during the acoustic survey by the R/V “Ushio Maru” in late 1993.
    Three types of echo, namely, near surface echo patches, near bottom echo patches and the sound scattering layer (SSL) in the middle layer, were recorded on the echogram of the dual frequency quantitative echo sounder.
    Hydrographic data by CTD observation showed that cold and less salty water mass below 5°C and 33.5 layers on the bottom of the shelf of Oshima Peninsula then formed a water front along the boundaries to surrounded the warmer and more salty waters.
    By comparing the hydrographic and acoustic dana, the sound scattering layer appeared along the water front and demersal echo patches were found in great numbers in the cold water mass, Activity of fishing boats and hydrographic conditions in this area suggested that the demersal echo patches were the schools of walleye pollock which were migrating for spawning and the sound scattering layer consisted of zooplankton aggregation in the water front.
    Distribution of the echograms indicated that the height of fish schools were 1 to 4 meters and the SV of the echo were about -65 to -60 dB. The density of the schools of walleye pollock along the transects were 5.8 in November to 8.1 shoals/nautical mile in December, respectively.
  • DooJin Hwang, Kohji Iida, Tohru Mukai
    Nippon Suisan Gakkaishi (Japanese Edition) 61 (1) 43 - 50 1349-998X 1995 [Not refereed][Not invited]
     
    This paper discusses methods for the stable bottom detection and the optimum bottom offset which enable to separate the fish echoes from the bottom echoes with echo integration of demersal fish. In preprocessing of the echo signal, the bottom detection has to be done stably against the fluctuation of echo level and the bottom offset has to be set to a minimum height such that near bottom fish echoes are included. Two methods of bottom detection, namely echo level threshold method and maximum echo slope method were compared and analyzed. The echo level method works well if the ideal threshold level was given but it sometimes misses the bottom because of the fluctuation of the echo. Another method to detect the bottom which uses maximum echo slope indicates the simple and stable bottom detection. In addition, the bottom offset has to be set near to the bottom but not to include the bottom echo. Optimum bottom offset should be set a few samples before the detected bottom echo which relates the beginning of pulse shape and acoustic beam pattern to the bottom feature. © 1995, The Japanese Society of Fisheries Science. All rights reserved.
  • MUKAI Tohru, IIDA Kohji
    Fisheries Science Japanese Society of Fisheries Science 61 (4) 647 - 652 0919-9268 1995 [Not refereed][Not invited]
     
    The diurnal variation of the dorsal aspect target strength of encaged fish was investigated, and an attempt was made to estimate the fish tilt angle distributions. The experiment was conducted at Lake Kuttara in Hokkaido. In this lake, kokanee Oncorhynchus nerka are the dominant species. The net cage was made of nylon monofilament, had a volume of approximately one cubic meter, and was nearly acoustically transparent. Five kokanees, caught by gill net, were released into the net cage. During the experiment periods, the net cage was kept at a depth of 10 m under the transducer which was driven by a 50 kHz transmitter. About 600 echoes from encaged fish occurring over a 24 hour period were measured and analyzed. The results obtained were as follows: 1) The shape of the dorsal aspect target strength probability density functions (PDFs) of encaged fish showed a large variation before and after sunrise and sunset. 2) Diurnal variation of the averaged dorsal aspect target strength of encaged fish was about 18 dB. 3) Some of the observed target strength PDFs agree approximately with estimated target strength PDFs based on fish tilt angle distribution which was assumed to truncated normal distribution.
  • IIDA Kohji, MUKAI Tohru
    Fisheries Science Japanese Society of Fisheries Science 61 (4) 641 - 646 0919-9268 1995 [Not refereed][Not invited]
     
    Acoustic surveys for studying the behavior of kokanee Oncorhynchus nerka in Lake Kuttara, Hokkaido, have been conducted over the past ten years and several interesting results have been obtained. Kokanee were recorded on echograms as school echoes in the daytime and as numerous individual echoes in the nighttime. Their swimming layer changes seasonally in accordance with the depth change of thermocline in the lake. Kokanee also have a diurnal behavioral pattern. Namely, they form schools after sunrise and they disperse after sunset. The shifting process from individuals to schools or from schools to individuals is strongly related to illuminance, and it takes 50 minutes at sunrise and sunset for the change to occur. The swimming speed of kokanee in the daytime is faster than that in the nighttime, and the fastest speed of the day occurs at twilight. Average swimming speeds were estimated to be 57 cm/s in the twilight, 48 cm/s in the daytime and 20 cm/s in the nighttime periods, respectively.
  • 桜井 泰憲, 向井 徹, 朴 容石
    日本水産學會誌 日本水産學會 60 (4) 467 - 472 0021-5392 1994/07 [Not refereed][Not invited]
  • Mukai Tohru, Sano Noritatsu, Iida Kohji, Sasaki Seiji
    NIPPON SUISAN GAKKAISHI 日本水産學會 60 (2) 215 - 222 0021-5392 1994 [Not refereed][Not invited]
     
    The target strength (TS) of fish varies with acoustic frequency, fish size, fish activity, orientation, swimbladder and so on. Among these, the swimbladder is recognized as having the most important effect on TS. The dorsal aspect TS as a function of tilt angle of fish caught by bottom trawling in the East China Sea was measured at two frequencies (25 and 100 kHz). The swimbladder sizes (length and height) and inclination angle of the swimbladder to the lateral line of the fish were measured by X-ray photographs. TS and swimbladder data were then compared and analyzed, and the following results were obtained:
    (1) The eight species of fish, except the silver pomfret, have swimbladders, but the angle and size of the swimbladder varies.
    (2) For bladder fish, the angle of the maximum dorsal aspect TS agrees with the broadside direction of the swimbladder.
    (3) The dorsal aspect TS of the silver pomfret is clearly lower than that of bladder fish at the two frequencies.
    (4) The maximum and averaged dorsal aspect TS values of the silver pomfret, were lower by about 7-8 dB, 8-10 dB at 25 kHz, and by 8-10 dB, 9-11 dB at 100 kHz than two other bladder fish (yellow sea bream and whitefin crevalle).
  • Mukai Tohru, Sano Noritatsu, Iida Kohji, Sasaki Seiji
    NIPPON SUISAN GAKKAISHI 日本水産學會 60 (2) 223 - 227 0021-5392 1994 [Not refereed][Not invited]
     
    The dorsal aspect target strength (TS) of four live swimming crab Portunus trituberculatus were measured at 25kHz and 100kHz in Cheju port (Korea). Probability density functions (PDF), i.e., Rayleigh PDF and Rice PDF, were fitted to the distribution of backscattering amplitude from the live swimming crab. The following results were obtained:
    (1) TS was more dispersed at 100kHz than at 25kHz.
    (2) The PDFs of the backscattering amplitude agree approximately with Rice PDF at 25kHz and with Rayleigh PDF at 100kHz.
    (3) The Rice parameter γ tends to decrease with increasing carapace length, carapace width and acoustic frequency.
    (4) The averaged TS , estimated from PDFs, is about 2dB higher at 25kHz than at 100kHz.
    (5) Mean values of averaged target strength B, which is normalized with respect to body weight, are -52.5dB at 25kHz, -54.9dB at 100kHz. These values agree approximately with those of bladder fish.
  • Yong-Seok Park, Yasunori Sakurai, Tohru Mukai, Kohji Iida, Noritatsu Sano
    NIPPON SUISAN GAKKAISHI 60 (4) 467 - 472 1349-998X 1994 [Not refereed][Not invited]
     
    In the spawing season, sound production of captive walleye pollock Theragra chalcogramma (Pallas) was examined by the grunt call projection method. The pollock emitted four patterns of grunt calls, namely threatening call, aggressive-attacking call, courting call, and mating call. The sound frequency of these grunt calls is less than 800 Hz. The characteristics of walleye pollock behaviour matching each grunt call are as follows: (1) Only one threatening grunt call was emitted by the superior male to threaten other males encountered. (2) Aggressive-attacking grunt calls were emitted from two to five times in order to drive out other males from the male's occupied space. Behaviour included chasing, dorsal mounting and lateral mounting. (3) Courting calls were emitted from six to twelve times in order to court other males and females which are characterized by swimming faster than usual. The behaviour included chasing, dorsal mounting and lateral mounting. (4) Mating grunt calls were made more than thirteen times in order to mate with mature females. Behaviour included chasing, and dorsal, lateral and ventral mounting. © 1994, The Japanese Society of Fisheries Science. All rights reserved.
  • Park Yong-Seok, Sakurai Yasunori, Mukai Tohru, Iida Kohji, Sano Noritatsu
    NIPPON SUISAN GAKKAISHI 日本水産學會 60 (4) 467 - 472 0021-5392 1994 [Not refereed][Not invited]
     
    In the spawing season, sound production of captive walleye pollock Theragra chalcogramma (Pallas) was examined by the grunt call projection method. The pollock emitted four patterns of grunt calls, namely threatening call, aggressive-attacking call, courting call, and mating call. The sound frequency of these grunt calls is less than 800 Hz. The characteristics of walleye pollock behaviour matching each grunt call are as follows:
    (1) Only one threatening grunt call was emitted by the superior male to threaten other males encountered.
    (2) Aggressive-attacking grunt calls were emitted from two to five times in order to drive out other males from the male's occupied space. Behaviour included chasing, dorsal mounting and lateral mounting.
    (3) Courting calls were emitted from six to twelve times in order to court other males and females which are characterized by swimming faster than usual. The behaviour included chasing, dorsal mounting and lateral mounting.
    (4) Mating grunt calls were made more than thirteen times in order to mate with mature females. Behaviour included chasing, and dorsal, lateral and ventral mounting.
  • 黄 斗湊, 佐野 典達, 飯田 浩二, 向井 徹, 増田 紀義, 佐々木 成二
    北海道大學水産學部研究彙報 北海道大学 44 (4) 197 - 208 0018-3458 1993/11 [Not refereed][Not invited]
  • Mukai Tohru, Sano Noritatsu, Iida Kohji, Sasaki Seiji
    NIPPON SUISAN GAKKAISHI 日本水産學會 59 (9) 1515 - 1525 0021-5392 1993 [Not refereed][Not invited]
     
    The dorsal aspect target strength functions of ten species of fish collected by bottom trawl were measured at two frequencies. The average TS were calculated with respect to fish tilt angle distribution, which is assumed to have a mean value of -5 degrees and a standard deviation of 15 degrees. Both maximum TS and average TS were normalized with the fish length (L[cm]) squared and the 2/3 power of body weight (W[g]), namely,
    TS=20logL+A, TS=20/3log W+B.
    The results obtained were as follows:
    (1) The target strength is generally higher at low frequency (25kHz) than at high frequency (100kHz). But for two species (Chub mackerel and Kandari), neither maximum nor average TS differ between low and high frequencies.
    (2) The target strength of Silver pomfret, a bladderless fish, is clearly lower than that of bladder fish at two frequencies.
    (3) The normalized TS (A or B) were calculated for the maximum TS (Amax or Bmax) and average TS (Aavg or Bavg). The results are: Amax = -63 - -59 dB, Aavg = -68 - -64 dB at low frequency; Amax = -65 - -59 dB, Aavg = -72 - -65 dB at high frequency, and Bmax = -52 - -45 dB, Bavg = -57 - -50 dB at low frequency; Bmax = -54 - -45 dB, Bavg = -60 - -52 dB at high frequency.
  • MUKAI T.
    Bulletin of the Faculty of Fisheries,Hokkaido University 北海道大學水産學部 42 (3) p90 - 97 0018-3458 1991/08 [Not refereed][Not invited]
  • Iida Kohji, Mukai Tohru, Ishii Kiyohiko
    NIPPON SUISAN GAKKAISHI 日本水産學會 57 (4) 623 - 627 0021-5392 1991 [Not refereed][Not invited]
     
    This paper discusses the application of a dual beam echo sounder to the estimation of fish length.
    The dual beam method is typically used for measurement of the in situ target strength of fish. The in situ target strength is an important parameter, not only for obtaining the echo integrator scaling factor but also for estimating the fish length that is related to target strength.
    A prototype dual beam echo sounder system with computer technology was developed and used in the acoustic survey conducted at Lake Kuttara. Kokanee Oncorhynchus nerka is abundant in this lake.
    Many individual echoes were recorded using the dual beam echo sounder and target strength data were collected.
    Converting target strength, TS, into body length, l, was done using the following relational formula:
    TS(dB)=20logl(cm)-66.0
    Results of the analysis indicated that both the distributions of target strength and body length which were estimated by the dual beam method agreed to the catch data obtained from net sampling.
  • 飯田 浩二, 向井 徹, 石井 清彦
    Bulletin of the Faculty of Fisheries,Hokkaido University 北海道大學水産學部 41 (4) p200 - 204 0018-3458 1990/11 [Not refereed][Not invited]
  • 石井 清彦, 飯田 浩二, 向井 徹
    Bulletin of the Faculty of Fisheries,Hokkaido University 北海道大學水産學部 40 (4) p307 - 312 0018-3458 1989/11 [Not refereed][Not invited]
  • MUKAI Tohru, SUZUKI Tsuneyoshi, SANO Noritatsu, IIDA Kohji
    Bulletin of the Faculty of Fisheries,Hokkaido University 北海道大學水産學部 39 (2) p106 - 114 0018-3458 1988/05 [Not refereed][Not invited]

MISC

Presentations

Association Memberships

  • Asian Fisheries Acoustics Society   日本水産学会   海洋調査技術学会   海洋音響学会   アメリカ音響学会   

Works

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Pioneering)
    Date (from‐to) : 2020/07 -2026/03 
    Author : 山口 篤, 松石 隆, 向井 徹, 藤森 康澄, 別府 史章
     
    本年度は北海道大学大学院国際食資源学院漁業管理論の一環として「かいあし漁業ワークショップ」を、2020年11月12日～13日にかけて北大函館キャンパスにて開催した。参加者は留学生を中心とする20名弱で、言語は英語で行った。またかいあし漁業に関連する海産動物プランクトンを対象とした漁業として、ナンキョクオキアミ漁業に関する勉強会も開催した。ナンキョクオキアミは、単一生物としては地球上で最も生物量バイオマスの多い種として知られ、人類の食糧資源として注目され、日本も1970年代から漁業を行っていたが、採算ベースに乗らず、2011/2012年を最後に撤退している。ナンキョクオキアミについては、現在はクリルオイルを対象とした漁業がノルウェーを中心に行われている。ノルウェーのナンキョクオキアミ漁業はサプリメントを主要商品としており、漁獲後船上でサプリメントまでを加工する設備を整えた専用船を持ち、MSC認証を受けた企業がある。オキアミ類を対象とした漁業は、日本でも岩手県三陸沖にて、春先にツノナシオキアミを対象とする「イサダ漁」があり、そこで採集されたオキアミを使って「イサダオイル」の開発もなされている。一方、かいあし漁業を行っている企業は世界で唯一、ノルウェーのトロムセーにあり、その主要商品は「Calanus Oil」である。このCalanusとは、ノルウェー海で優占する年1世代を持つ大型カイアシ類Calanus finmarchicusやCalanus hyperboreusの名称である。北大西洋におけるCalanusに比較し得る、北太平洋の種はNeocalanus属で、Neocalanus属は年1世代の世代時間を持ち、体内に油分を貯める性質を持っている。このNeocalanus属を対象とした漁業の確立実行可能性を探るのが重要であるということが、初年度の調査研究の結論としてあげられる。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2022/03 
    Author : MUKAI Tohru
     
    The acoustic characteristics of pointhead flounder were investigated by field surveys and tank experiments to realize their acoustic resource survey. We accumulated basic information necessary for acoustic resource surveys and identified the optimum survey season. First, in the field survey, we examined the characteristics of the fish schools of pointhead flounder captured by the quantitative echo sounder, and found that they were patchy in the mid-water layer. Next, tank experiments were conducted to investigate the acoustic characteristics and differences in their behavior during the day and night, as a result, acoustic surveys of pointhead flounder should be conducted during the daytime. Finally, we investigated the differences in the frequency characteristics and the echo shapes by the quantitative echo sounder in field surveys of other fish species and zooplankton overlapping with pointhead flounder, and proposed the method for discriminating these species.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)
    Date (from‐to) : 2017/06 -2020/03 
    Author : Sawada Kouichi
     
    By using multiple frequencies, it is possible to distinguish between zooplankton such as euphausiids and fish and to estimate the body length. But until now, it was difficult to introduce them in fishing boats because its cost and space for several transducers to be installed. Previous research has revealed that newly developed broadband transducer can transmit and receive multiple frequencies with a single transducer. However, it takes much time to calculate the layout of many elements (array layout) which satisfies the required performance at each frequency. Therefore, we introduced a genetic algorithm used to obtain optimal values in other fields, developed a method for performing the array layout calculation in a short time, and confirmed it through experiments. To verify the design parameters, we have developed a method to reduce the measurement error in the experiment.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Date (from‐to) : 2014/04 -2018/03 
    Author : MUKAI TOHRU
     
    This application was aimed at developing a method of quantifying zooplankton inhabiting the ocean twilight zone with depths of 200 to 500 meters using a combination of the acoustic and the optical method. Using the acoustic method, besides krill, which has many examples of measurements up to now, it was also possible to measure the acoustic scattering cross-section which is the scale factor in quantification for copepods and amphipods. On the other hand, with the optical method, it was possible to photograph zooplankton at depths of up to 100 meters using a general-purpose digital camera with external flash. Further shooting at greater depths could not be realized due to troubles in the equipment.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Date (from‐to) : 2013/04 -2016/03 
    Author : Amakasu Kazuo, MUKAI Tohru, SASAKURA Toyoki
     
    A broadband echosounder which can use high-frequency linear FM signals was built. The usable frequency range is 250 to 700 kHz and is suitable for zooplankton observation. A calibration method using a 38.1-mm diameter tungsten carbide sphere was established for this echosounder. This method uses a specular echo from the sphere, which can obtained by applying the pulse compression processing to the received echo and improving the range resolution. Spectrum measurement for a 20.6-mm sphere and 20 to 40-mm-long shrimps was conducted in a tank and then we confirmed that specific spectra which depend on targets can be obtained. The results of this study are useful for developing a new zooplankton observation method.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)
    Date (from‐to) : 2011/04 -2015/03 
    Author : AMAKASU Kazuo, MUKAI Tohru, MOTEKI Masato, SASAKURA Toyoki
     
    A broadband echosounder with a broadband transducer using multilayer piezoelectric actuators (elements) and related analysis methods were developed. The features of this system are that a broadband sound with a frequency band of 20-200 kHz can be transmitted and received, and acoustic scattering spectra of marine organisms such as fish and zooplankton can be determined from their echoes. Since the acoustic scattering spectra include their biological information (e.g., species or taxon, size, and behavior), the biological information can be determined without net sampling. This technology allows surveys of the marine organisms by observation platforms in which net samplings are impossible (e.g., AUV and glider). This technology can be applied to fisheries and to observations for gas bubbles and seafloor.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Date (from‐to) : 2009 -2011 
    Author : MUKAI Tohru, SAWADA Kouichi
     
    Properties of the animal's acoustic scattering(Target Strength : TS) were investigated in copepods which have the highest population among zooplanktons living in the ocean. TS of copepods were measured in a sea-water tank, and estimated using the theoretical model by measuring the acoustic parameters. Both TS were compared. As a result, it was confirmed that TS estimates matched the actual measurements of some individuals well while entirely differed with other individuals. When the differences were investigated, it was found that the former individuals did not have oil sac into the copepods body while the latter individuals had oil sac. We will further investigate this difference in detail.
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    Date (from‐to) : 2005 -2007 
    Author : 向井 徹, 山本 潤
     
    本研究では,水中ロボットカメラ(ROV)によって得られた水中映像に計量魚群探知機による音響映像を組み合わせ,水中映像の定量化技術の開発を開発することを目的としている.さらに,近年,注目されている現象を対象とし,その現象のメカニズム解明のための基礎的なデータを取得することも目指し,本研究では,その被害が問題となった日本海の大型くらげを主な対象として研究した.具体的には,平成18年度に北海道大学水産学部付属練習船おしょろ丸(船底装備の計量魚群探知機を装備)の日本海調査(9月下旬〜10月上旬)に乗船し,北海道奥尻島沿岸から本州・日本海沿岸域で大型くらげの目視調査を行った.ROVによる大型くらげの観察は,目視観察により大型くらげが高密度で分布する海域で実施した。この調査では,船上から,水中遊泳するクラゲの視認が困難である場合も,ROVを用いることにより,その鉛直的な分布特性のデータを取得することができ,さらに,これらの大型クラゲの分布深度では,計量魚群探知機においても,大型クラゲからのエコーを確認することができた。平成19年度では,単なるエコーグラム上での確認ではなく,その分布密度,サイズを検出するために,クラゲの音響的な特性を解析した。その結果,クラゲの音響散乱強度は,体サイズよりも周波数や遊泳姿勢などに強く影響を受けることが明らかになった。今後,ROVによって遊泳姿勢とサイズを測定し,音響データと併せて解析することによリクラゲの浮遊分布の定量化が可能となると考えられる。また本研究で解析した手法を他の魚種,プランクトンなどに応用することによって,水中映像の音響データによる定量化が十分可能であると考えられる。本研究の成果は現在投稿中である。
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    Date (from‐to) : 2003 -2005 
    Author : 飯田 浩二, 向井 徹, KANG Donhyug, TANG Yong, 佐藤 正典
     
    医療用超音波診断装置を耐圧容器に入れた水中音響ヵメラを用いて海洋生物を至近距離から観察し,生物の形状,姿勢,骨格、体内器官,行動などを定量的に測定する無侵襲の生物計測手法の開発を目的とした。1.水中超音波カメラの改良原型の医療用超音波診断装置は焦点距離が30cmなので,制御ソフトウェアを改造し,最大焦点距離2.4mまでの高解像度の水中音響画像を取得できるようにした。さらに,音響カメラと水中光学カメラを並置させ,光学/音響画像を同時に表示させるようにした。また,、水槽観察においては自動直線走査装置(リニアステージ)を用いて魚体内部の生体構造を糖密観察できるようにした。2.水槽飼育生物の音響画像の解析リニアステージを用いることにより,さらに高解像度の音響画像を得ることができ,魚類の脊椎骨,浮袋,肝臓,生殖腺等の形状を非破壊測定し,解剖結果と比較して,10%以下の誤差で測定できた。特に生殖腺の音響画像に着目し,外形からは判別が不可能なマダラの雌雄の判別を可能にした。さらにマダラ,サケ,スケトウダラ,ハタハタなどの卵巣体積めほか音響画像の解析により卵粒径の大きさを推定した。3.現場海洋生物の音響画像の解析昨年と同様に北海道南茅部町の水深12mの海底に音響カメラを設置し,約1週間生物観察をおこなった。ホッケ,アイナメ,タコ,クラゲ,ヒトデ,カジなど多くの生物が音響画像に記録され,光学カメラ画像から,対象生物を確認することができた。夜間にはヨコエビや動物プランクトンの群れが海藻の内部から間歇的に出入りする様子が確認された。また,出現生物の体長や遊泳速度を推定することができた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2003 -2005 
    Author : IIDA Kohji, YOSHIMURA Yasuo, MUKAI Tohru, MIYASHITA Kazushi
     
    The scanning sonar can detect fish school much wider area in the water compared to an echo sounder. The purpose of this study is to develop the new generation quantitative scanning sonar to measure the shape, the volume and the density of the fish school for fisheries survey.1)The quantitative sonar we developed was installed on the fishing boat in Norway and we measured the fish school volume with purse seine fishing for herring and blue whiting. The new sonar was also tested in domestic fishing ground with purse seine fishing for mackerel, squid and yellow tail. Fish schools were detected more than 3,000 meters far from the boat, and the good linear relationship between estimated volume and the catch were found.2)To estimate density of fish school by echo integration method, the target strength in side aspect is necessary. We measured the 3-dimensional target strength of anchovy in sonar frequencies. The target strength in side aspect agreed well to the TS in dorsal aspect, and it showed the "8" figured directional pattern.3)To calculate fish number from the fish school volume, the specific occupation volume by a single fish (Tv) is required. We estimated Tv of walleye pollock dividing the volume backscattering strength (Sv) of fish school by the target strength of fish. Results showed that the Tv is proportional to the 2.6th power of the body length.4)Using the successive multiple sonar images of fish school obtained by the vertical mode, the three dimensional shape of fish school was reconstructed by 3D image processing techniques.5)Results of the study were presented at fisheries and acoustics symposiums. Some of them were applied for domestic and international patents.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2002 -2004 
    Author : FUJIMORI Yasuzumi, MUKAI Tohru, YAMASHITA Nariharu
     
    This study is consist of two kinds of categories as shown below.1.Development of automated opening/closing system for WYSIWYG-Net: Automated opening/closing system to achieve the multi-layer sampling for plankton and micro-nekton was developed. This system could be worked without an armored cable winch system and allows to conduct multi-layer sampling on any research vessel.2.Utilization of LOPC (Laser Optical Plankton Counter) with net : The platform unit was made for zooplankton sampling with LOPC and the data from the net and LOPC were compared. From these results, the methods to estimate the density and to make a species distinction for zooplankton (krill, copepoda, etc.) were developed.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2001 -2003 
    Author : SAITOH Sei-ichi, IIDA Koji, MIURA Teisuke, MUKAI Toru, YONETA Kunisaburo, FUJIMORI Yasuzumi
     
    It is very important that we develop multi-dimensional sensing in combined with satellite remote sensing, underwater remote sensing and direct survey to predict when, where and how much are marine living resources available. Objectives of this study are to develop methodology of multi-dimensional sensing of marine living resources and their environment and to monitor three-dimensional distributions of Japanese common squid and three dimensional environment using acoustic with towed body transducer and real-time towing CTD system with satellite images. Major results are as follows :(1)Observation depth of real-time towing CTD system is from 10 meter to 80 meter in the condition of the length of wire of 300 meter and ship running speed of 10 knot.(2)Three-dimensional observation in the southeastern Bering Sea was successful to gather environmental structure and biomass of fishes using real-time towing CTD and acoustic system EK500. Visualization those three-dimensional distribution was established using AVS software.(3)In the First Oyashio intrusion region off Cape Erimo, three-dimensional fine structure was observed using real-time towing CTD system and acoustic system.
  • 日本学術振興会：科学研究費助成事業 奨励研究(A)
    Date (from‐to) : 2000 -2001 
    Author : 向井 徹
     
    1.プランクトンの生体密度および生体内音速の測定:今年度の動物プランクトンの採集は,4月から11月にかけて北海道噴火湾において行ない,この海域の優占種であるツノナシオキアミの生体密度および生体内音速の測定を行なった。測定法は例年行なっているdensity bottle法およびTime of flight法によった。その結果,噴火湾のツノナシオキアミの生体密度は体長にあまり依存せず,ほぼ一定の値になることが示唆された。2.プランクトンの音響反射率の測定:動物プランクトンの音響反射率の実測を,周波数170kHzと230kHzの2周波数を備えた低ノイズ型TS測定装置で行なった。前年度に明らかになった送受波器の指向性の影響は,送受信系の改造により,かなり低減されていた。活きたツノナシオキアミに麻酔をかけて,この装置を用いて音響反射を実測した。また,これと同時に,水中カメラを水槽内に設置し,ツノナシオキアミの姿勢を観察した。その結果,姿勢のちょっとした変化によりツノナシオキアミの音響反射率が大幅に変化し,本装置によってもノイズにマスクされ音響反射率が測定できない部分も見られた。しかし,これらの実測値と上記1のパラメータを用いて音響理論モデルから推定された音響反射率の間には,非常に良い一致を見る事が出来た。従って,ノイズにマスクされた部分も,モデルにより推定できると考える。また,本方法により,生体密度・生体内音速の季節変化に伴う音響反射率の変化を実測で把握することが出来,これをモデルで推定することも出来た。今後は,ツノナシオキアミ以外の動物プランクトンへの本方法の適用,低ノイズ型TS測定装置の更なる改良,および現場における音響反射率の測定を試み,動物プランクトンの音響調査手法の確立を目指してく。
  • 日本学術振興会：科学研究費助成事業 奨励研究(A)
    Date (from‐to) : 1998 -1999 
    Author : 向井 徹
     
    本年度は、実際に5月から9月にかけて、北海道噴火湾で捕獲した生きたツノナシオキアミの生体密度および生体内音速の測定を行った。測定法は前年度に確立した方法であり、生体密度の測定には海水とグリセロールの混合溶液を用いたdensity bottle法を用い、生体内音速の測定はTチューブを用いたTime of flight法によった。その結果、噴火湾のツノナシオキアミの生体密度は、いずれの月も体長の増加に伴って減少した。生体密度の季節的変化を見ると、同体長のツノナシオキアミでも、春季に小さく夏季に大きくなる傾向があった。また各月毎の平均生体密度をサンプル採集時の海水の密度で除した平均密度比も同様の季節的変化が見られ7月の方が6月より約1%大きかった。一方、音速比に関しても平均密度と同様に6月から7月にかけて約1%増加した。以上の測定により得られた各月毎の平均密度比、平均音速比を用いて音響理論散乱モデルからターゲットストレングス(TS)を推定し、季節によるTS変化を調べた。用いたモデルはオキアミを有限長のシリンダーに仮定する、有限長シリンダーモデルである。その結果、各月毎のツノナシオキアミのTSは同体長においても明確に異なっており、7月と9月ではそのTSは最大約5dB異なっていた。さらに平均密度比、平均音速比がともに約1%変化していた6月と7月では、算出されるTSが最大約3dB異なっていた。このことは、超音波反射の主要因である「うきぶくろ」を持たないオキアミのような生物のTSを推定する場合、単に体長を考慮する以上に密度比や音速比に適切な値を使わなければ、正確なTS推定ができないことを意味する。しかしこれら生体密度や生体内音速の季節的変化が、何に起因するかは今回の研究においては特定することができなかった。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for General Scientific Research (C)
    Date (from‐to) : 1994 -1995 
    Author : IIDA Kohji, MUKAI Tohru
     
    For the effective echo survey for fish resource estimation, the basic study has been conducted for two years and the following results were obtained.1.Data analysing system for echo survey using computer network was developed. It realized the parallel processing of data acquisition, analysis, and storage.2.High accuracy processing of the near bottom echo which is important for a demersal fish survey was investigated.3.Target strengths of juvenile swimbladder fish were measured. Juvenile fish often scatter acoustic waves well due to their resonance structure.4.The three-dimensional analysing method of scanning sonar which is effective tool for echo survey has developed.5.The new calibration procedure using standard sphere was proposed. It certifies to obtain the confident echoes from the standard target for calibration.6.Effective acoustic survey designs were discussed. The adaptive circumstance data, e.g., CTD data, Satellite image, ADCP data were gathered and generalized for echo data analysis.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for General Scientific Research (B)
    Date (from‐to) : 1991 -1993 
    Author : SANO Noritatsu, ISHII Kiyoshiko, KOBAYASHI genji, AKIBA Yoshio, MUKAI Tohru, IIDA Kohji
     
    We substantiated the NOAA series with enough information to support an ocean survey by research ship.We also need to try to research when an where the fishing grounds witll shift and whether these stocksa are going to increase, etc. Accordingly we need to accumulate and analyze the data and information by the use of a quantitative echo sounder and the use of several ships at the same time in order to make the plankton's biomass clear. In this case it would be more effective if quantitative echo sounder information were standardized.The other way to plan for the efficient use of stock and of fishing ground production, is to make very accurate recordsof the fishing and oceanic conditions of sardine, the Japanese common squid, etc. At the same time we would neet to, with the cooperation of national or private research institutions, continue with the systematization of collection, management, and reporting of the data of fishing and oceanic conditions.
  • 日本学術振興会：科学研究費助成事業 奨励研究(A)
    Date (from‐to) : 1992 -1992 
    Author : 向井 徹
  • 魚およびプランクトンによる音響散乱に関する研究
    Date (from‐to) : 1985
  • Studies on acoustic scattering signature of fish and zooplankton
    Date (from‐to) : 1985

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