Researcher Profile and Settings

Master

Affiliation (Master)

• Field Science Center for Northern Biosphere　Aquatic Research Station

Affiliation (Master)

• Field Science Center for Northern Biosphere　Aquatic Research Station

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Profile and Settings

Profile and Settings

• Name (Japanese)

  Yamamoto

• Name (Kana)

  Jun

• Name

  200901041193354595

Achievement

Research Areas

• Life sciences / Ecology and environmental science

Education

•        - 1997  Hokkaido University
•        - 1997  Hokkaido University  Graduate School, Division of Fisheries
•        - 1996  Hokkaido University
•        - 1996  Hokkaido University  Graduate School, Division of Fisheries
•        - 1994  Hokkaido University  School of Fisheries Sciences
•        - 1994  Hokkaido University  Faculty of Fisheries
•        - 1993  Hokkaido University  School of Fisheries Sciences
•        - 1993  Hokkaido University  Faculty of Fisheries

Awards

• 2021/11 Asian Fisheries Acoustics Society Young Fisheries Acoustician Award
   Broadband target strength measurements of three bladderless fishes. 

  受賞者: Yan N, Mukai T, Hasegawa K, Yamamoto J and Fukuda Y
• 2017/12 日本DNA多型学会 優秀研究賞
   

  受賞者: 時岡駿;柳本卓;山本潤;桜井泰憲
• 2016/04 Best student Award Best student Award
   

  受賞者: YAMAMOTO Jun

Published Papers

• Broadband target strength of arabesque greenling, Pacific sand lance, and pointhead flounder

  Naizheng Yan, Tohru Mukai, Kohei Hasegawa, Jun Yamamoto, Yoshiaki Fukuda

  ICES Journal of Marine Science 81 (1) 195 - 203 1054-3139 2023/12/12 

  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.
• 水槽実験によるスルメイカの擬餌針捕捉行動の観察.

  松井萌, 山本潤

  水生動物. 2023 AA2023-2012.  2023/07 [Refereed]
  
• Genetic evidence for multiple mating and mixing of sperm from multiple males in the seminal receptacles of female Japanese flying squid (Todarodes pacificus)

  Ryusei Ohtani, Jun Yamamoto, Takashi Yanagimoto, Kohsuke Adachi, John R Bower, Hidefumi A Fujioka, Miyuki Hirose, Mitsuhiro Nakaya, Satoshi Suzuki, Shun Tokioka

  Journal of Molluscan Studies 88 (3) 0260-1230 2022/09/19 

  ABSTRACT The genetic diversity of sperm and spermatangia stored by mated Japanese flying squid (Todarodes pacificus) was examined to better understand how this ommastrephid squid mates and stores sperm. Analyses were conducted using spermatangia implanted in the lips of immature squid collected in Tsugaru Strait, northern Japan, in July–August 2019, spermatangia implanted in the lips of mature squid collected in the East China Sea in April 2019, and sperm stored in the seminal receptacles of squid collected off Tosashimizu, Kochi Prefecture, Japan, in February 2019. DNA was extracted, microsatellite loci were amplified using five PCR primers, and allele peaks were analysed. Analysis of the spermatangia confirmed that females in the field mate with multiple males, suggesting that males transfer from 1 to at least 14 spermatangia in each mating. Analysis of the seminal receptacles showed that sperm from multiple males are mixed within individual sperm chambers. Spermatangia were also found implanted in the lips of males, providing evidence of same-sex sexual behaviour. To date, studies of cephalopod mating systems have focused on coastal species, and the results of this study add to our growing knowledge of more oceanic species.
• Negative temperature dependence of statolith Sr/Ca and its intraspecific variability in experimentally maintained spear squid Heterololigo bleekeri

  Shota Hosono, Takahiro Irie, Jun Yamamoto, Mitsuhiro Nakaya, Yasunori Sakurai, Tomohiko Kawamura, Yoko Iwata

  Journal of the Marine Biological Association of the United Kingdom 1 - 7 0025-3154 2022/08/19 [Refereed]
   

  Abstract The strontium-to-calcium ratio (Sr/Ca) in aragonitic shells and statoliths often depends on temperature, and has been investigated for its potential availability as a sclerochronological record of the temperatures experienced during the life of the animal. Only a few cephalopod species have been subjected to rearing experiments to validate the temperature dependence of statolith Sr/Ca despite the strong demand for estimating their historical ecology, particularly of migratory squid populations. In this context, we examined the relationship between temperature and statolith Sr/Ca in the spear squid, Heterololigo bleekeri, by maintaining wild-caught immature individuals at one of three constant temperatures: 12, 14 or 16°C. A portion of statolith precipitated during the experiment was optically identified by daily increment analysis, and then subjected to Sr/Ca measurement using an electron probe micro-analyser. Regression analysis (N = 29) demonstrated the dependence of statolith Sr/Ca on temperature and the relationship was estimated as an equation Y = 9.93 (±0.29) − 0.11 (±0.02) X. However, ~90% of the total residual variance was accounted for by the among-individual variation of statolith Sr/Ca within each temperature group. Consequently, the 95% confidence interval ranged over ± 7.85°C when the temperature was estimated by inserting a Sr/Ca value into this equation. The statolith Sr/Ca values are unlikely to provide reliable estimates for absolute temperatures, but it may allow reconstruction of a time-series of relative temperatures experienced by a particular individual.
• Genetic and morphological differentiation among local populations of Japanese top shell Turbo sazae.

  TAKASHI YANAGIMOTO, SEINEN CHOW, TAKESHI SAKAI, SHUHEI SAWAYAMA, YORIKO HAYASHI, KAZUYUKI SAITO, TOSHIE WAKABAYASHI, JUN YAMAMOTO

  NIPPON SUISAN GAKKAISHI 0021-5392 2022 [Refereed]
  
• The Effect of Low Temperature on the Early Life Stages of the Walleye Pollock, Gadus chalcogrammus—A Laboratory Study

  Hae-Kyun Yoo, Woo-Jin Kim, Hyung-Jun Lim, Soon-Gyu Byun, Jun Yamamoto, Yasunori Sakurai

  Journal of Marine Science and Engineering 9 (8) 818 - 818 2021/07/28 

  The walleye pollock Gadus chalcogrammus is an important commercial species in Japan whose larvae and eggs may be negatively affected by the cold water mass from the coastal Oyashio current that is present in the spawning ground of the Japanese Pacific stock of this species. Therefore, we investigated egg and larval specific density, larval mortality, and behavioral response to temperature change during the ontogenetic development of the walleye pollock to understand the effect of this cold surface water mass (<1.5 °C). Egg and larval specific density varied during development but were lower than the corresponding values from the coastal Oyashio waters. Within our study temperature range (0.3–10.0 °C), the number of days to 50% mortality (D50) was high at 3.1 °C. Below and above this temperature, the D50 showed a decreasing trend. Regarding larval response, at 1.5°C and 5.0°C, newly hatched larvae occurred abundantly in the surface layer, irrespective of the surface and rearing temperatures. When these larvae were released into a thermally stratified water column (surface: 1.5 °C, bottom: 5.0 °C), larvae reared at 5.0 °C with the mouth open and yolk sac completely absorbed moved to the lower layers. However, larvae reared at 1.5 °C remained in the surface layer. These results suggest that the cold water mass could negatively affect larval survival and may limit the escape ability of larvae from unfavorable cold conditions.
• Estimating Pot Mesh Selectivity for Corn Stripe Shrimp Pandalus hypsinotus by Water Tank Experiment

  光崎健太, 藤森康澄, 山本潤, 富安信, 有馬大地, 澤村正幸, 清水晋

  水産工学 57 (3) 91 - 97 0916-7617 2021/02 [Refereed]
  
• Abundance, horizontal and vertical distribution of epipelagic ctenophores and scyphomedusae in the northern Bering Sea in summer 2017 and 2018: Quantification by underwater video imaging analysis

  Marie Maekakuchi, Kohei Matsuno, Jun Yamamoto, Yoshiyuki Abe, Atsushi Yamaguchi

  Deep Sea Research Part II: Topical Studies in Oceanography 181-182 104818 - 104818 0967-0645 2020/12 [Refereed]
  
• Swimming speed of Japanese flying squid Todarodes pacificus when attracted by white LED light stimulation

  HAJIME MATSUI, GO TAKAYAMA, JUN YAMAMOTO, YASUZUMI FUJIMORI, YASUNORI SAKURAI

  NIPPON SUISAN GAKKAISHI 86 (2) 59 - 66 0021-5392 2020/03/15 [Refereed][Not invited]
  
• Close-up observations on the spawning behavior of a captive Japanese flying squid (Todarodes pacificus)

  Jun Yamamoto, Kohsuke Adachi, John R. Bower, Hajime Matsui, Mitsuhiro Nakaya, Ryusei Ohtani, Pandey Puneeta, Satoshi Suzuki, Shun Tokioka, Dharmamony Vijai, Takashi Yanagimoto, Hae-Kyun Yoo

  SCIENTIFIC REPORTS 9 2045-2322 2019/12 [Refereed][Not invited]
   

  The spawning behavior of a Japanese flying squid (Todarodes pacificus) is described based on up-close observation of a captive female. The squid was first transferred from a 10-ton tank to a polystyrene plastic box containing 45 liters of seawater. About one hour later, the mantle-contraction rate increased rapidly, followed by a brief convulsion of the mantle and arms and a whitening of the body. The mantle contractions become shallow and rapid, and several seconds later, semitransparent jelly presumably from the nidamental glands emerged from the funnel and passed between the ventral pair of arms. Approximately 90 seconds after the egg mass first emerged, the female began ejecting oocytes through the funnel into the egg mass using rapid, powerful mantle contractions. Soon after the oocytes were ejected, translucent strands (presumably sperm) emanated from the buccal membrane. The female continued to eject oocytes for approximately two minutes, after which the mantle convulsed, and the mantle-contraction rate decreased slowly for about one minute until the contractions stopped. The squid died soon afterwards.
• Acoustic discrimination between juvenile walleye pollock and pointhead flounder

  Naizheng Yana, Tohru Mukai, Jun Yamamoto, Kohei Hasegawa

  Fisheries Research 2019/11 [Refereed][Not invited]
  
• Optical and acoustic camera observations of the behavior of the Kuril harbor seal Phoca vitulina stejnegeri after invading a salmon setnet

  Fujimori Y, Ochi Y, Yamasaki S, Ito R, Kobayashi Y, Yamamoto J, Tamaru O, Kuramoto Y, Sakurai Y

  Fisheries Science 84 (6) 953 - 961 2018/11 [Refereed][Not invited]
  
• Orientation Patterns of Japanese Flying Squid Todarodes pacificus Embryos within Egg Masses and Responses of Paralarvae to Light

  Puneeta P, Vijai D, Yamamoto J, Sakurai Y

  Zoolog Sci 35 293 - 298 2018/08 [Refereed][Not invited]
  
• Structure and properties of the egg mass of the ommastrephid squid Todarodes pacificus

  Pandey Puneeta, Dharmamony Vijai, Jun Yamamoto, Kohsuke Adachi, Yoshiki Kato, Yasunori Sakurai

  PLOS ONE 12 (8) 1932-6203 2017/08 [Refereed][Not invited]
   

  The Japanese flying squid, Todarodes pacificus, is thought to spawn neutrally buoyant egg masses that retain a specific location in the water column by floating at the interface between water layers of slightly different densities. It is important to understand the physical process that determines the vertical distribution of the egg masses to predict their horizontal drift in relation to embryo survival and subsequent recruitment. Here, mesocosm experiments were conducted in a 300 m(3) tank by creating a thermally stratified (17-22 degrees C) water column to obtain egg masses. A cage net methodology was developed to sustain egg masses for detailed observation. We measured the density of the egg masses of T. pacificus, and used this information to infer the vertical distribution patterns of the egg masses at the spawning grounds (Tsushima Strait, Japan). When measured separately, the density of the outer jelly of each egg mass was 2.7 sigma units higher than that of the surrounding water. The outer jelly and the specific gravity of embedded individual eggs (similar to 1.10) cause the egg masses to have very slight negative buoyancy relative to the water in which they are formed. Analysis of the vertical profile of the spawning ground showed that water density (sigma theta) in-creased sharply at similar to 30 m depth; thus, egg masses might settle above the pycnocline layer. In conclusion, we suggest that T. pacificus egg masses might retain their location in the water column by floating at the interface between water layers of slightly different densities, which happen to be above the pycnocline layer (actual depth varies seasonally/annually) in the Tsushima Strait between Korea and Japan.
• Diets and body condition of polar cod (Boreogadus saida) in the northern Bering Sea and Chukchi Sea

  Tsubasa Nakano, Kohei Matsuno, Bungo Nishizawa, Yuka Iwahara, Yoko Mitani, Jun Yamamoto, Yasunori Sakurai, Yutaka Watanuki

  POLAR BIOLOGY 39 (6) 1081 - 1086 0722-4060 2016/06 [Refereed][Not invited]
   

  To understand trophic responses of polar cod Boreogadus saida (a key species in Arctic food webs) to changes in zooplankton and benthic invertebrate communities (prey), we compared its stomach contents and body condition between three regions with different environments: the northern Bering Sea (NB), southern Chukchi Sea (SC), and central Chukchi Sea (CC). Polar cod were sampled using a bottom trawl, and their potential prey species in the environment were sampled using a plankton net and a surface sediment sampler. Polar cod fed mainly on appendicularians in the NB and SC where copepods were the most abundant in the environment, while they fed on copepods, euphausiids, and gammarids in the CC where barnacle larvae were the most abundant species in plankton samples on average. The stomach fullness index of polar cod was higher in the NB and SC than CC, while their body condition index did not differ between these regions. The lower lipid content of appendicularians compared to other prey species is the most plausible explanation for this inconsistency.
• Distribution pattern of Polar cod (Boreogadus saida) larvae and larval fish assemblages in relation to oceanographic parameters in the northern Bering Sea and Chukchi Sea

  Yui Kono, Hiroko Sasaki, Yukari Kurihara, Amane Fujiwara, Jun Yamamoto, Yasunori Sakurai

  POLAR BIOLOGY 39 (6) 1039 - 1048 0722-4060 2016/06 [Refereed][Not invited]
   

  Polar cod, Boreogadus saida, is a key species in the Arctic Ocean ecosystem. We examined the distribution pattern of B. saida and other fish larvae in relation to oceanographic parameters, including sea surface temperature and salinity (SST and SSS), the mode of temperature and salinity within the water column (F (temp) and F (sal)), and the temporal duration between the date of sea ice retreat and the date of field surveys (dSRT) in the northern Bering Sea and Chukchi Sea during the summers of 2008 and 2013. Sampling was conducted onboard the T/S Oshoro-Maru using a bongo net for 2 years. At sampling stations, the temperature and salinity were measured using conductivity-temperature-depth profiler casts. We calculated dSRT from satellite derived polar gridded sea ice concentration data. A total of 1186 individuals comprising 7 families and 16 species were collected, with B. saida (35 %) and Ammodytes hexapterus (27 %) dominating the catch in number. Based on the species composition (cluster analysis), the sampling stations were divided into four groups. Pleuronectidae dominated group A, which was characterized by relatively high temperature (SST and F (temp)), while B. saida dominated group B, characterized by low temperatures. A. hexapterus dominated group C and D, which had similar temperatures and salinities, but group C had a shorter dSRT than group D. The latter was also differentiated by the presence of Lumpenus sp. B. saida, which were most abundant in regions where temperatures ranged from -2 to 0.5 A degrees C. These results, the geographical variation of group B sampling stations, suggest there are two separate spawning areas characterized by similar fish communities and related to consistently cold bottom temperatures. Moreover, stations with a higher abundance of smaller sized larval B. saida were characterized by a short dSRT, whereas stations with a lower abundance and a larger size were characterized by a long dSRT.
• Male copulatory behavior interrupts Japanese flying squid Todarodes pacificus female spawning activity

  Pandey Puneeta, Dharmamony Vijai, Jun Yamamoto, Yasunori Sakurai

  MARINE ECOLOGY PROGRESS SERIES 551 277 - 281 0171-8630 2016/06 [Refereed][Not invited]
   

  Batch spawning, intermittent spawning and multiple spawning represent common reproductive strategies among cephalopods. These flexible spawning strategies are also common in fishes, and are thought to be a female trait that is programmed depending on environmental parameters. The ommastrephid squid Todarodes pacificus, being a terminal spawner, is considered to have a single spawning event, extruding one large egg mass and dying soon thereafter. Females that are interrupted by males exhibiting mating behavior, while extruding the egg mass, spawn multiple egg masses over the course of 2-3 d instead of dying soon after spawning the first egg mass. We demonstrate that male mating behavior causes 'forced' intermittent spawning by females (i.e. more than one spawning event). We hypothesize that in T. pacificus, some males use this strategy to mate with females unable to repel advances while spawning, thus providing the male with the opportunity to contribute sperm and enhance gene flow.
• A Red-footed Booby Catching Airborne Squid

  MURAMATSU Kouta, YAMAMOTO Jun, ABE Takuzo, NISHIZAWA Bungo, HOSHI Naoki, OHWADA Maki, WATANUKI Yutaka, SAKURAI Yasunori

  山階鳥類学雑誌 山階鳥類研究所 47 (2) 130‐135 - 135 1348-5032 2016/03/20 [Refereed][Not invited]
  
• Interactive effects of incubation temperature and salinity on the early life stages of pacific cod Gadus macrocephalus

  Xiaodong Bian, Xiumei Zhang, Yasunari Sakurai, Xianshi Jin, Ruijing Wan, Tianxiang Gao, Jun Yamamoto

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 124 117 - 128 0967-0645 2016/02 [Refereed][Not invited]
   

  The combined effects of incubation temperature and salinity on the early life stages of Pacific cod Gadus macrocephalus were examined under controlled laboratory conditions. Data were collected from two synchronized experiments. Experiment 1 was designed to evaluate the interactive effects of incubation temperature and salinity on the hatchability of fertilized G. macrocephalus eggs. Experiment 2 was set up to evaluate the interactive effects of incubation temperature and salinity on the time from hatching to 50% mortality of the non-fed yolk-sac larvae (M-50). The results show that temperature could significantly influence the development and hatchability of the larvae, as well as the hatching characteristics of G. macrocephalus. Viable hatch was significantly influenced by salinity when the upper and lower thermal limits were approached and shows the synergism of low salinity on egg development at low temperatures and conversely inhibitory effects of low-salinity at high-temperatures. Data on developmental rates as influenced by temperature were presented at each tested salinity level. No influence of salinity was found at the temperature levels tested. Dome-shaped quadratic curves were fitted to the relationship between temperature and the incidence of larval size and yolk storage at hatch for most of the tested salinity levels. The effect of salinity across all temperatures, however, had a much smaller influence on larval size and no effect on yolk storage at hatch. The influence of temperature on larval duration (time from hatching to M-50) could be described in all cases by an exponential power function. Evidence on the synergism of low salinity at low-temperatures and conversely inhibitory effects of low salinity at high-temperatures was also observed. The results were discussed in reference to salinity modified temperature effects on the early life stages of G. macrocephalus. Maximum hatchability and larval size at hatch, and moderate salinity tolerance and larval duration suggest an optimal temperature range of 4 degrees C to 6 degrees C for the survival and development of the early life stages of G. macrocephalus in the field. (C) 2015 Elsevier Ltd. All rights reserved.
• Vertical position, specific gravity and swimming ability of Pacific cod Gadus macrocephalus yolk-sac larvae reared at four temperatures

  Zhe Li, Jun Yamamoto, Yasunori Sakurai

  FISHERIES SCIENCE 81 (5) 883 - 889 0919-9268 2015/09 [Refereed][Not invited]
   

  Vertical position and movement rate were measured in the yolk-sac larvae of the Pacific cod Gadus macrocephalus at different rearing temperatures (3, 5, 7, and 9 A degrees C) and an identical temperature of 5 A degrees C in experimental columns during the initial 3 days post-hatch (dph). Larval specific gravity was also measured through sinking velocities. Yolk-sac larvae swam upward and initially (0 dph) remained in the upper section of the experimental column through intermittent upward swimming, and gradually moved to near-neutral buoyancy at 3 dph at corresponding rearing temperatures. Rearing temperature significantly affected the swimming ability: at 0 dph, vertical movement rates measured at 5 A degrees C were low in the yolk-sac larvae reared at warm temperatures. However, no such difference was observed at 3 dph. The difference in vertical movement rate may have resulted from the temperature-mediated body sizes (standard length) and yolk-sac sizes (yolk-sac volume) at hatching. Specific gravity did not change for the varying temperatures during the initial 3 days, but decreased as ontogeny progressed. Therefore, we suggest that Pacific cod yolk-sac larvae achieve a demersal-pelagic habitat transition through upward swimming and increasing buoyancy.
• The Effect of Warmer Water Temperature of Walleye Pollock (Gadus chalcogrammus) Larvae

  Yoo H-K, Byun S-G, Yamamoto J, Sakurai Y

  Journal of the Korean Society of Marine Environment & Safety 21 (4) 339 - 344 2015/08 [Refereed][Not invited]
  
• Laboratory observations on the vertical swimming behavior of Japanese common squid Todarodes pacificus paralarvae as they ascend into warm surface waters

  Hae-Kyun Yoo, Jun Yamamoto, Tomonori Saito, Yasunori Sakurai

  FISHERIES SCIENCE 80 (5) 925 - 932 0919-9268 2014/09 [Refereed][Not invited]
   

  This study examined the effect of warm temperature on the survival of paralarvae of Japanese common squid Todarodes pacificus and on their swimming behavior as they ascended to the surface. Observations were conducted on paralarvae in Petri dishes and in 85-cm-tall, cylindrical tanks that had a warmer upper layer and cooler lower layer separated by a small thermocline. Paralarvae were obtained through artificial fertilization and reared in Petri dishes at six experimental temperatures between 20.9 and 30.4 A degrees C. Paralarvae reared at lower temperatures survived longer than those reared at warmer temperatures, and survival decreased at temperatures above 24 A degrees C. When the mean temperatures in the upper layer of the tanks were 24.4-26.0 A degrees C, the paralarvae ascended through the thermocline to the surface, but when the mean temperatures in the upper layer were 29.7-29.8 A degrees C, paralarvae stopped ascending at the thermocline. These results show that paralarvae have a temperature preference but ascend to the surface in the unfavorable temperature range. The results suggest that increasing surface temperatures at spawning grounds will negatively affect both the survival and behavior of T. pacificus paralarvae.
• Envelope surface ultrastructure and specific gravity of artificially fertilized Pacific cod Gadus macrocephalus eggs

  X. Bian, X. Zhang, Y. Sakurai, X. Jin, T. Gao, R. Wan, J. Yamamoto

  JOURNAL OF FISH BIOLOGY 84 (2) 403 - 421 0022-1112 2014/02 [Refereed][Not invited]
   

  The envelope surface ultrastructure and specific gravity of artificially fertilized eggs of the Pacific cod Gadus macrocephalus were examined. The unfertilized, demersal and slightly adhesive eggs of G. macrocephalus were almost spherical and had no oil globules. Wrinkled envelope surface with elaborated hexagonal reticulated patterns and type I micropyle were observed under a scanning electron microscope. The adhesiveness of the eggs was lost at the blastodermal-cap stage after fertilization. The micropylar canal was sealed by secretion of the perivitelline fluid, and the entire surface became rough. Numerous bacilli were deposited at the micropyle and the outer envelope surface at the late germ-ring stage and at the embryo five-eighths around the yolk stage. The micropyle was completely deformed at the embryo seven-eighths around the yolk stage. The specific gravity of the fertilized G. macrocephalus eggs ranged from c. 1.0316 to 1.0454. These values, however, sharply decreased towards the end stages of egg development to produce pelagic larvae. The ultrastructural changes in the micropyle and envelope surface of the G. macrocephalus eggs protected the embryo from microorganism infections and mechanical stress during the long incubation period. The adhesiveness and specific gravity of the eggs influenced their dispersion potential. (C) 2014 The Fisheries Society of the British Isles
• Temperature-mediated survival, development and hatching variation of Pacific cod Gadus macrocephalus eggs

  X. Bian, X. Zhang, Y. Sakrai, X. Jin, T. Gao, R. Wan, J. Yamamoto

  JOURNAL OF FISH BIOLOGY 84 (1) 85 - 105 0022-1112 2014/01 [Refereed][Not invited]
   

  Laboratory-validated data on the survival, development and hatching responses of fertilized Pacific cod Gadus macrocephalus eggs from the northern Japan stock were determined through an incubation experiment. The optimum temperature for survival until hatching ranged from 4 to 8 degrees C. No significant difference in development rates was found between the populations from Mutsu Bay, Japan, and western Canadian coastal waters even though the samples may belong to different G. macrocephalus stocks. Gadus macrocephalus larvae hatched asynchronously from egg batches despite incubation under the same environment during their development. Both incubation temperature and temperature-mediated hatch rank affect size and yolk reserve. These data suggest that variations in water temperatures within an ecological range markedly influence the development rates, survival and hatching of the eggs, as well as the stage at hatch larvae of G. macrocephalus. Asynchronous hatching and the production of offspring with variable sizes and yolk reserves are considered evolutionary bet-hedging strategies that enable the species to maximize their likelihood of survival in an environment with variable temperatures.
• Oceanic squid do fly

  K. Muramatsu, J. Yamamoto, T. Abe, K. Sekiguchi, N. Hoshi, Y. Sakurai

  MARINE BIOLOGY 160 (5) 1171 - 1175 0025-3162 2013/05 [Refereed][Not invited]
   

  Using powerful jet propulsion, some squid species are able to exit the water and become airborne; this is a common behavior seen throughout the world's oceans. However, direct scientific observation is rare, with most studies relying on anecdotal evidence and limited photographic documentation. Here, we examine the flying behavior of young oceanic squid (Ommastrephidae) observed in sequential photographs taken in the Northwest Pacific (35(o)34.0'N, 146(o)19.3'E) on July 25, 2011. We define four phases in the flight process: launching, jetting, gliding and diving. During flight, squid actively change their aerial posture and attitude depending on the flight phase and their distance from the water. The present study demonstrated that flight of squid is not simple gliding after incidental exit from the water, but involves jet propulsion, generation of lift force and control of different body postures in different flight phases, which have evolved to enhance escape from predators.
• Development of a Battery Powered Compact 2000m Class ROV System and Its Method of Operation

  山本 潤, 岩森 利弘, 星 直樹, 阿部 拓三, 坂岡 桂一郎, 亀井 佳彦, 高木 省吾, 沼本 修, 阪 幸宏, 桜井 泰憲, 末岡 和久, 有村 博紀, 渡邉 日出海

  水産技術 水産総合研究センター 5 (2) 171 - 174 1883-2253 2013/02 [Refereed][Not invited]
   

  本研究では支援船に大型特殊な設備を必要とせずに運用が可能な2,000m級小型ROVシステムの開発と運用法を構築した。本システムはランチャ内に搭載したリチウムイオンバッテリからビークルとランチャに電源を供給し，またランチャをロープで垂下することにより汎用の設備による巻上／下げで潜航／浮上が可能となっている。当初の運用ではランチャに接続する一次ケーブルと水中の荷重を支えるロープとに複雑な絡みが発生したが，絡みを軽減させる器具と低伸縮のロープを用いることにより解消しその運用法を確立した。
• Brooding in a Gonatid Squid off Northern Japan

  John R. Bower, Katsunori Seki, Tsunemi Kubodera, Jun Yamamoto, Takahiro Nobetsu

  BIOLOGICAL BULLETIN 223 (3) 259 - 262 0006-3185 2012/12 [Refereed][Not invited]
   

  Brooding of egg masses by a squid in Japan is described. Brooding females were photographed in situ, and the females, their eggs, and their hatchlings were collected. The squid had all undergone gelatinous degeneration and swam slowly and continuously by undulating the fins and expelling water sporadically through the funnel. Eggs were held together by a dark, viscous material that formed a single-layer, sheet-like mass, from which hatchlings were seen to emerge. The annual appearance of brooding females in surface waters during spring suggests that they transport their egg masses from deep water to the surface before the eggs hatch. Genetic analyses identified the squid as Gonatus madokai (family Gonatidae), now the second gonatid and third squid known to brood.
• Effect of temperature on swimming behavior of paralarvae of the Japanese common squid Todarodes pacificus

  YAMAMOTO Jun, MIYANAGA Sachi, FUKUI Shin'ichi, SAKURAI Yasunori

  水産海洋研究 水産海洋学会 76 (1) 18 - 23 0916-1562 2012/02/01 [Not refereed][Not invited]
  
• Cold-adapted structural properties of trypsins from walleye pollock (Theragra chalcogramma) and Arctic cod (Boreogadus saida)

  Gaku Kanno, Hideki Kishimura, Jun Yamamoto, Seiichi Ando, Takeshi Shimizu, Soottawat Benjakul, Sappasith Klomklao, Sitthipong Nalinanon, Byung-Soo Chun, Hiroki Saeki

  EUROPEAN FOOD RESEARCH AND TECHNOLOGY 233 (6) 963 - 972 1438-2377 2011/12 [Refereed][Not invited]
   

  Complementary DNA clones encoding trypsins were isolated from pyloric ceca of cold-adapted fish, walleye pollock (Theragra chalcogramma) (WP-T) and Arctic cod (Boreogadus saida) (AC-T). The isolated full-length cDNA clones of WP-T and AC-T were 852 and 860 bp, respectively, and both cDNAs were contained an open reading frame of 726 bp. WP-T and AC-T seemed to be synthesized as preproenzyme that contains a signal peptide, an activation peptide, and a mature trypsin. Although the amino acid sequence identities of WP-T and AC-T to that of bovine trypsin were 64 and 63%, respectively, they completely conserved the structural features for catalytic function of trypsin. On the other hand, WP-T and AC-T possessed the four Met residues (Met135, Met145, Met175 and Met242) in their molecules and the deletion of Tyr151 and substitution of Pro152 for Gly in their autolysis loops when aligned with the sequences of tropical-zone fish and bovine trypsins. In addition, the contents of charged amino acid residues at the N-terminal regions (positions 20-50) of WP-T and AC-T were extremely higher than those of other fish and bovine trypsins. Moreover, one amino acid (Asn72) and two amino acids (Asn72 and Val75) coordinating with Ca(2+) in bovine trypsin were exchanged for another amino acids in WP-T (His) and AC-T (His and Glu), respectively, and the contents of negative charged amino acids at their Ca(2+)-binding regions were lower than those of tropical-zone fish and bovine trypsins. Therefore, it was considered that these structural characteristics of WP-T and AC-T are closely related to their lower thermostability.
• Effects of environmental variability on the spawning areas, catch, and recruitment of the Japanese common squid, Todarodes pacificus (Cephalopoda: Ommastrephidae), from the 1970s to the 2000s

  A. L. Rosa, J. Yamamoto, Y. Sakurai

  ICES JOURNAL OF MARINE SCIENCE 68 (6) 1114 - 1121 1054-3139 2011/07 [Not refereed][Not invited]
   

  The Japanese common squid, Todarodes pacificus, is one of the most commercially valuable squids in the world. It spawns almost throughout the year, with a seasonal peak in autumn and winter. Long-term changes in sea surface temperature (SST) and its effect on the spawning areas and catch of T. pacificus were analysed for 27 spawning seasons (September April 1978-2006) in the Sea of Japan and East China Sea. The spawning area was inferred between the limits of 21-41 degrees N and 121-142 degrees E, 100-500-m depth, the mean Kuroshio axis, and the 19.5-23 degrees C SST range. The results revealed that the area surrounding Kyushu Island is gaining importance as a spawning area. In addition, the discontinuity of the spawning ground in the East China Sea (around 29 degrees N 128 degrees E) during the winter spawning period was demonstrated to be associated with a decrease in the catches by both the Japanese and the Korean fleets. This constriction of the spawning ground would act as an obstacle to either the adult squid, making it difficult for them to reach the most southern grounds, or the paralarvae and juveniles, which, because of adverse environmental conditions, might not be able to survive the early stages of the feeding migration.
• Effect of artificial light on sampling with plankton net for euphausiid

  Yasuzumi Fujimori, Tohru Mukai, Jun Yamamoto

  NIPPON SUISAN GAKKAISHI 日本水産學會 76 (6) 1080 - 1082 0021-5392 2010/11 [Not refereed][Not invited]
  
• Transitions in purse seine fishing in the southwestern Sea of Japan after the second half of the 1980s

  SHIMURA Tsuyoshi, MASUDA Shinya, UJI Ryosuke, YAMAMOTO Jun, SAKURAI Yasunori

  Bulletin of the Japanese Society of Fisheries Oceanography 水産海洋学会 74 (2) 98 - 104 0916-1562 2010/05/01 [Not refereed][Not invited]
  
• Observations of food falls off the Shiretoko Peninsula, Japan, using a remotely operated vehicle

  Jun Yamamoto, Takahiro Nobetsu, Toshihiro Iwamori, Yasunori Sakurai

  FISHERIES SCIENCE 75 (2) 513 - 515 0919-9268 2009/04 [Refereed][Not invited]
  
• Maturation and spawning of the Japanese anchovy in the Sea of Japan off the Tottori coast during spring

  SHIMURA Tsuyoshi, YAMAMOTO Jun, MORIMOTO Haruyuki, OHSHIMO Seiji, SHIMOYAMA Syunichi, SAKURAI Yasunori

  Bulletin of the Japanese Society of Fisheries Oceanography 水産海洋学会 72 (2) 101 - 106 0388-9149 2008/05/28 [Not refereed][Not invited]
  
• Transportation of organic matter to the sea floor by carrion falls of the giant jellyfish Nemopilema nomurai in the Sea of Japan

  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.
• Vertical distribution of Todarodes pacificus (Cephalopoda : Ommastrephidae) paralarvae near the Oki Islands, southwestern Sea of Japan

  Jun Yamamoto, Tsuyoshi Shimura, Ryosuke Uji, Shinya Masuda, Shuyo Watanabe, Yasunori Sakurai

  MARINE BIOLOGY 153 (1) 7 - 13 0025-3162 2007/11 [Refereed][Not invited]
   

  The diel vertical distribution patterns of Japanese common squid, Todarodes pacificus, paralarvae were examined using a Multiple Opening Closing Net and Environmental Sensing System (MOCNESS) in the southwest Sea of Japan near the Oki Islands (Japan) during five late-autumn surveys in 1998-2002. A total of 1,511 paralarvae ranging in mantle length (ML) from 0.7 to 7.3 mm were collected at 63 of the 68 stations surveyed. Most (84%) were collected above 75 m depth and in the mixed layer. The vertical distribution patterns varied little between day and night. Hatchling-sized (< 1.0 mm ML) paralarvae were abundant at 0-25 m depth, and paralarval ML increased with increasing sampling depth. Our results suggest that T. pacificus paralarvae do not exhibit large diel vertical migration patterns, but as they increase in size, paralarvae gradually descend in the water column and the variability in depth increases with ontogeny.
• Measurements of specific density of and sound speed in nomura's jellyfish Nemopilema nomurai to estimate their target strength using a theoretical scattering model

  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 [Not refereed][Not invited]
   

  The jellyfish <I>Nemopilema nomurai</I>, 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.
• Interannual fluctuations in recruitment of walleye pollock in the Oyashio region related to environmental changes

  Osamu Shida, Tomonori Hamatsu, Akira Nishimura, Akifumi Suzaki, Jun Yamamoto, Kazushi Miyashita, Yasunori Sakurai

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 54 (23-26) 2822 - 2831 0967-0645 2007 [Refereed][Not invited]
   

  The Japanese Pacific walleye pollock (Theragra chalcogramma) stock is the largest stock of this species in Japanese waters. It is a key component of the Oyashio ecosystem. In southern Hokkaido waters, these fish spawn mainly during January and February near the mouth of Funka Bay (FB), and most eggs and larvae are transported into FB. During midsummer juvenile pollock migrate along the southern coast of Hokkaido to a nursery ground on the continental shelf off eastern Hokkaido (Doto area). However, some eggs and larvae are transported southward to the Tohoku region (TR). Transport depends largely on the Oyashio. which generally flows southward along the eastern coasts of Hokkaido and Tohoku. Thus, this stock has two different recruitment routes: FB-Doto and FB-TR. In the 1980s, when the southward flow of the Oyashio was strong, the number of age-2 pollock estimated from a virtual population analysis (VPA) indicated that recruitment to the entire stock remained at a medium level. In the 1990s, when the Oyashio weakened, strong year-classes occurred in 1991. 1994, and 1995, but not in the latter half of the 1990s. Juvenile catches in the TR by commercial fisheries, which can be taken as indices of recruitment level via FB-TR, were high during the 1980s and decreased in the 1990s. Although there was no significant difference in the average number of recruits between the 1980s and the 1990s as estimated from a VPA, the recruitment patterns differed between the two decades. Here, we propose that recruitment routes of this stock shifted in response to environmental changes. (C) 2007 Elsevier Ltd. All rights reserved.
• Possible spawning ground by the Japanese common squid, Todarodes pacificus, at Yamato Rise centred sea of Japan.

  Shimura T, Yamamoto J, Kamei Y, Sakurai Y

  Phuket Mar Biol Cent Res Bull 66 267 - 273 2005 [Refereed][Not invited]
  
• Trial Observation of the Sound Scattering Layer Using an ROV

  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 [Not 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.
• Investigation on the early stages of the ommastrephid squid Todarodes pacificus near the Oki Islands (Sea of Japan)

  J Yamamoto, S Masuda, K Miyashita, R Uji, Y Sakurai

  BULLETIN OF MARINE SCIENCE 71 (2) 987 - 992 0007-4977 2002/09 [Not refereed][Not invited]
   

  The MOCNESS (Multiple Opening Closing Net and Environmental Sampling System) was used to investigate the distribution of the early life stages of the Japanese common squid Todarodes pacificus in the southwest Sea of Japan near the Oki Islands, a suspected spawning ground of this species. The largest catches of hatchling-sized paralarvae occurred at the surface layer (0-25 in), and paralarval mantle lengths increased with increasing sampling depth, suggesting that T pacificus paralarvae gradually descend in the water column life cycle as they grow. There was no clear difference in the horizontal distribution among the different size groups.
• Stock fluctuations of the Japanese common squid, Todarodes pacificus, related to recent climate changes

  Yasunori Sakurai, Hidetada Kiyofuji, Sei-ichi Saitoh, Jun Yamamoto, Tsuneo Goto, Ken Mori, Takahiro Kinoshita

  FISHERIES SCIENCE 68 226 - 229 0919-9268 2002 [Refereed][Not invited]
   

  In Todarodes pacificus, recruitment success is most likely dependent on the physical and biological environments of the spawning and nursery grounds. Annual catches of T. pacificus in Japanese and Korean waters have markedly increased since the late 1980s and the recent catch is equal to that of the 1960s. Here re-proposed is a possible scenario for the stock increase since the late-1980s based on GIS analysis of changes in the inferred spawning area during 1984-1999. This study suggests that winter-spawning areas in the East China Sea shrank when adult stocks decreased during a cool regime, and that fall and winter spawning areas extended and overlapped in the Sea of Japan and East China Sea when adult stocks increased during a warm regime. We conclude that stock fluctuations in T. pacificus occur with annual changes of winter-spawning areas related to climatic regime shifts.
• Net mesh retention of Japanese common squid eggs and paralarvae

  J Yamamoto, T Miyoi, Bower, JR, T Goto, Y Nakamura, S Masuda, Y Sakurai

  NIPPON SUISAN GAKKAISHI 日本水産學會 67 (3) 497 - 499 0021-5392 2001/05 [Not refereed][Not invited]
   

  スルメイカの幼生分布調査で使用するNIP#40とNMG52の網目による受精卵およびふ化幼生の保持状況について調べた。NMG52では卵・ふ化幼生のほぼ全てが保持されたが, NIP#40上では卵・ふ化幼生が高い割合で網目を通過することが示唆された。分布調査による幼生を用いてNIP#40上に高い割合で保持される幼生サイズを推定すると, その外套長は1.26mm以上であった。
• Identifying fish species around the Oki island using echogram analysis

  Tadanori Fujino, Ryousuke Uji, Kazushi Miyashita, Koutarou Tetsumura, Shinya Masuda, Jun Yamamoto

  Proceedings of the ACOUSTGEAR2000 1 89 - 97 2001 [Refereed][Not invited]
  
• Distribution of Todarodes pacificus (Cephalopoda : Ommastrephidae) paralarvae near the Kuroshio off southern Kyushu, Japan

  Bower, JR, Y Nakamura, K Mori, J Yamamoto, Y Isoda, Y Sakurai

  MARINE BIOLOGY 135 (1) 99 - 106 0025-3162 1999/10 [Not refereed][Not invited]
   

  The distribution and abundance of Japanese common squid [Todarodes pacificus (Steenstrup, 1880)] paralarvae off southern; Kyushu Island near the Ku-roshio were examined in relation to water types in the region. Surveys were conducted in 1996 and 1997 using paired, 70 cm diameter Bongo nets. Temperature-salinity plots from 0, 50 and 100 m depths were used to assign sampling stations to three water types: inshore, mixing and Kuroshio. In total, 4103 T. pacificus paralarvae were collected at 59 of 72 stations. Catch densities at positive stations ranged between 8 and 4282 ind./50 m(2) sea surface area. Catches during both years were highest in mixing waters, followed by inshore and Kuroshio waters. Total catches were highest just north of the oceanographic front at the inshore edge of the Kuroshio and declined with increasing distance away from the front. Catches of paralarvae less than or equal to 1.0 mm mantle length also peaked near the front. In both years, greater than or equal to 85% of all paralarvae and greater than or equal to 69% of those less than or equal to 1.0 mm mantle length occurred less than 25 km from the front. We conclude that most spawning off southwest Kyushu occurs near the frontal zone, where Kuroshio and inshore waters meet.
• Transport of the ommastrephid squid Todarodes pacificus under cold-water anesthesia

  Bower, JR, Y Sakurai, J Yamamoto, H Ishii

  AQUACULTURE 170 (2) 127 - 130 0044-8486 1999/01 [Not refereed][Not invited]
   

  We describe a method for transporting live squid, Todarodes pacificus (Cephalopoda: Ommastrephidae), using cold-water anesthesia. Squid were placed individually in 30-l plastic bags with 5 1 of 0-1 degrees C seawater and 10-15 l of oxygen gas. Thirteen of 14 anesthetized squid survived 6.5 h transport by car and airplane with no signs of distress or shock. The longest survival under anesthesia was 10 h. (C) 1999 Elsevier Science B,V. All rights reserved.

MISC

• Broadband target strength characteristics of Pacific herring (Clupea pallasii) and Pacific chub mackerel (Scomber japonicus) by a tether method

  WANG Zi, YAN Naizheng, 長谷川浩平, 向井徹, 山本潤  海洋音響学会研究発表会講演論文集  2024-  2024
• Broadband target strength of Japanese flying squid

  YAN Naizheng, 向井徹, 長谷川浩平, 工藤尚之, 大西由利子, 笠井昭範, 西山義浩, 山本潤  海洋音響学会研究発表会講演論文集  2024-  2024
• スケトウダラ稚魚のターゲットストレングスの体長依存性および周波数特性

  閻乃箏, 向井徹, 長谷川浩平, 山本潤  日本水産学会大会講演要旨集(CD-ROM)  2023-  2023
• Broadband target strength characteristics of juvenile walleye pollock

  YAN Naizheng, 向井徹, 長谷川浩平, 山本潤  海洋音響学会研究発表会講演論文集  2023-  2023
• Wideband target strength characteristics of bladderless fishes with different body shapes

  YAN Naizheng, 向井徹, 長谷川浩平, 山本潤, 福田美亮  海洋音響学会研究発表会講演論文集  2021-  2021
• 北海道噴火湾のトヤマエビPandalus hypsinotus Brandtの活動性

  光崎健太, 藤森康澄, 清水晋, 山本潤  日本水産学会大会講演要旨集  2019-  2019
• 水槽実験によるトヤマエビに対するかご網地の網目選択性の評価

  藤森康澄, 光崎健太, 清水晋, 山本潤  日本水産学会大会講演要旨集  2019-  2019
• Acoustic distinction between pointhead flounder and juvenile walleye pollock by echo shape and frequency characteristics

  Naizheng Yan, Tohru Mukai, Jun Yamamoto  2018 OCEANS - MTS/IEEE KOBE TECHNO-OCEANS (OTO)  2018/12/04  [Refereed][Not invited]
   

  © 2018 IEEE. This study addresses the methods for distinguishing the pointhead flounder Cleisthenes pinetorum from the juvenile walleye pollock Gadus chalcogrammus in and near Funka Bay, Hokkaido, Japan. Acoustics data of th Gadus chalcogrammus e fish were monitored using a Simrad EK60 (38, 120, 200 kHz) split-beam echo sounder, and biological samples were collected using a rod for the pointhead flounder and a frame-type midwater trawl for the juvenile walleye pollock. The pointhead flounder schools presented a patch shaped echo on the echograms and showed strong scattering at all three frequencies, whereas the distribution patterns of the juvenile walleye pollock schools were layered. The volume backscattering strength (SV) of the target schools extracted from the echograms showed that the pointhead flounder presented a higher SV at high frequency, which is consistent with the early surveys of other bladderless fish. In contrast, the juvenile walleye pollock showed higher SV at low frequency, which also agreed with the early surveys.
• Study on acoustic scattering characteristics of pointhead flounder Cleisthenes pinetorum―Characteristics of pointhead flounder observed with a quantitative echosounder―

  向井徹, YAN Naizheng, 山本潤, 長谷川浩平  電子情報通信学会技術研究報告  118-  (199(US2018 41-48))  29‐32  2018/08/23  [Not refereed][Not invited]
  
• Study on acoustic scattering characteristics of pointhead flounder Cleisthenes pinetorum―Target strength measurements of pointhead flounder using a broadband acoustic system―

  YAN Naizheng, 向井徹, 山本潤, 工藤尚之, 長谷川浩平  電子情報通信学会技術研究報告  118-  (199(US2018 41-48))  33‐36  2018/08/23  [Not refereed][Not invited]
  
• Stock fluctuation of fish and squid related to climatic regime shift: importance of the process study

  桜井 泰憲, 山本 潤  Kaiyo monthly  41-  (1)  33  -42  2009/01  [Not refereed][Not invited]
  
• Can we explain and predict stock fluctuation of the Japanese common squid, Todarodes pacificus related to climate change during the 20th-21st Century

  SAKURAI Yasunori, ROSA Ana Luisa, YAMAMOTO Jun  Program Abstr 5th World Fish Congr 2008  122  2008  [Not refereed][Not invited]
  
• スルメイカ

  桜井 泰憲, 森 賢, 後藤 常夫, 木所 英昭, 山本 潤, 岸 道郎, 中島 一歩  水産海洋研究  71-  (3)  220  -221  2007/08/31  [Not refereed][Not invited]
  
• スケトウダラ資源の長期変動との関係

  桜井 泰憲, 山本 潤, 本田 聡, 船本 鉄一郎, 八吹 圭三  水産海洋研究  71-  (2)  143  -145  2007/05/28  [Not refereed][Not invited]
  
• アラスカ漁業科学センター(米国シアトル)での研究生活

  山本 潤, 北大フィールド科セ  日本水産学会誌  72-  (1)  85  -85  2006/01/15  [Not refereed][Not invited]
  
• 気候のレジームシフトに連動したスルメイカの資源変動 (総特集 気候-海洋-海洋生態系のレジーム・シフト(上)実態とメカニズム解明へのアプローチ)

  桜井 泰憲, 山本 潤, 木所 英昭  海洋  35-  (2)  100  -106  2003/02  [Not refereed][Not invited]
  

Books etc

• Todarodes pacificus

  Sakurai Y, Kidokoro H, Yamashita N, Yamamoto J, Uchikawa K, Takahara H (Joint work249-272)
  Nova Science Publishers, Inc. 2013

Association Memberships

• 水産海洋学会   日本水産学会   

Research Projects

• How does ocean heat wave affect marine animal populations? Understanding the mechanisms of polymorphism in squid.

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2024/04 -2028/03 

  Author : 岩田 容子, 時岡 駿, 山本 潤, SANCHEZSILVA LUISGUSTAVO
• 最先端複合化学分析で明らかにするイカ類回遊生態：環境変動応答の理解の深化に向けて

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2024/04 -2028/03 

  Author : 石村 豊穂, 山本 潤, 瀬戸 陽一, 坂本 達也, 浅沼 尚, 鈴村 明政
• 多元素同位体の複合解析による回遊生物の新たな生物地球化学タグの確立

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2022/05 -2025/03 

  Author : 石村 豊穂, 山本 潤, 西田 梢, 則末 和宏, 田副 博文
• Study on the first food of Todarodes pacificus paralarvae focus on bacterial transmission between and mother-to-paralarvae

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2020/04 -2023/03 

  Author : 山本 潤, 足立 亨介, 柳本 卓, 中屋 光裕
• Elucidation of acoustic characteristics of the "floating pointhead flounder" by field and tank experiments and realization of acoustic survey of fisheries resources

  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.
• Development of shrimp pot with escape vent to prevent the catch of small individual of Corn-stripe shrimp in Funka-Bay, Hokkaido

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2018/04 -2021/03 

  Author : Fujimori Yasuzumi

   

  This study investigated a method to improve selectivity of shrimp pot aiming to protect the stock of Coonstripe shrimp Pandalus hypsinotus in the Funka-Bay, Hokkaido. It was found that small individuals were particularly active at night from the water tank experiment to investigate the behavior and diurnal activity. This suggested mesh size expansion and the installation of escape gap on pot for exclusion of small shrimp would be effective. The mesh selectivity of the pot was estimated by water tank experiments, and it was elucidated that 35 mm mesh size was suitable to protect individuals with 20 mm carapace length which correspond to the size of recruitment. Also, we confirmed that the circular escape gap with an inner diameter of 25 mm was expected to exclude the carapace length of 30 mm which correspond to the size after sexual conversion.
• Study on use of microbial loop by Japanese flying squid paralarvae

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2016/04 -2019/03 

  Author : YAMAMOTO Jun, SAKURAI Yasunori

   

  The present study examined the first food of Todarodes pacificus paralarvae by assuming that the paralarvae consume microorganisms which were produced by biological loop. The bacterial profile of the egg masses which were obtained through natural spawning in a large experimental tank was similar to those of the nidamental gland (the secretary organ of adult). This result suggested that the adhering bacteria might have originated from indigenous or symbiotic bacteria of the nidamental gland. While， metagenome analysis (CI1 and 16S-rRNA) on the gut contents which were extract from wild paralarvae by Laser Micro-dissection showed that the gut contents were consist of many species of eukaryote and prokaryote (the results on eukaryotic results may require additional testing). The result suggested paralarvae intake microorganism called “detritus”.
• Development of quantitative monitoring method for zooplankton inhabiting the ocean twilight zone

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific 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.
• Studies on stock fluctuation of seasonal cohorts of Japanese flying squid related to the success of reproduction and recruitment

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2013/04 -2016/03 

  Author : Sakurai Yasunori, YAMAMOTO Jun

   

  The experiment was conducted to test the reproductive hypothesis of Todarodes pacificus in a large tank (200 tons). The maturation process untill spawning were controled by temperatures during 13 and 20°C. Ripe females and males were released into the large tank.The egg masses were observed suspended in the thermocline. However, without the thermal gradient,egg masses collapsed on the bottom, and eggs were infested by microbes.Twenty-one females spawned 39 egg masses (30 to 120 cm diameter).The paralarvae survived for up to 13 days, which was suggested that they fed on DOM with marine bacteria. Annual catches of fall cohort are gradually decreasing after 2000s.The inferred spawning area was covered by warm surface water above 24°C . However, annual catches of winter cohort are stable after 2000s. The inferred spawning area was formed along continental slope in the East China Sea. The fishing area shifted to more northern area and the southward migration was delayed by December.
• A new method of measuring the size of fish on the image from digital camera

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2012/04 -2015/03 

  Author : FUJIMORI Yasuzumi, YAMAMOTO Jun

   

  This study aims to develop a new method of measuring the size of fish on the image from camera. The tank experiment was conducted using a digital camera and laser unit that generate flat beam. Further, sea experiment was done preparing a measuring system installed to watertight case that has capability of 300 m sea depth. The measurement error was 4 % in mean and up to 5 % in the tank experiment. In the sea experiment, the measuring system was hanged underwater from the ship. The fish that recognized as walleye pollock was observed. The estimated length accorded with the size of walleye pollock distributed in the experimental area.
• Initiation of sustainable trap cage fisheries improved by observation of behaviors of North Pacific giant octopus

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research

  Date (from‐to) : 2012/04 -2014/03 

  Author : SAKURAI Yasunori, NORO Kyosei, YAMAMOTO Jun

   

  North Pacific giant octopus is caught by the trap cage for octopus in the coast water of northern Japan. However, the catch is gradually decreasing after 2000. The causes were estimated by the bycatch of small octopus under 3kg BW and cannibalism between octopuses in cage. The aim of this study is to develop improved trap cage for escaping the small octopus. We observed some behaviors of giant octopus in captivity, such as entering into cage, positioning in cage, aggressive behavior and cannibalism between octopuses in cage. After that, we attached the several size of circular ring in the side net of cage. We found that small octopus under 3 kg can escape through the ring of 55 mm in diameter in the side net from cage. We also examined octopus behavior around the setting trap cages by biologging methods. Then, we confirmed that 3 kg octopus was not caught by the improved trap cage. This new trap cage will be more useful for the local octopus fisheries management in the northern Japan.
• クラゲ異常発生の行方とその大量の死骸が海洋生態系へ与えるインパクトの解明

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2008 -2010 

  Author : 山本 潤, 向井 徹

   

  本研究では主に大型クラゲを対象にし,近年,連続して発生している大型クラゲの異常発生に伴う,その大量の死骸が海洋生態系へ与えるインパクトを解明することを目的としている。初年度である20年度は,海底に沈降後の大型クラゲの死骸に誘引される生物を撮影するための一定間隔で撮影を行うタイム・ラプス・カメラシステムを2器作製してテストを実施してきたが,大型クラゲの大量発生はなく実海域での実験はできなかった。21年度は,本種が日本海に大量に出現する10月に北海道大学水産学部附属練習船おしょろ丸の日本海実習航海時に,隠岐諸島の南東の水深約240mの点にて,上記タイム・ラプス・システムを用いて,大型クラゲ死骸に誘引される生物の観察を行った。その結果,死骸が海底に到達してまもなく(約10分後)から,腐肉食者であるクモヒトデ,巻貝がクラゲ死骸に集まるのが観察できた。 最終年度である22年度は、当該大型クラゲの大発生が予測されたが、限定的な発生にとどまった。このような状況ではあったが、発生期の10月下旬におしょろ丸にて日本海の南西部において目視観測を実施したが、その分布は認められなかった。本研究で明らかにした水中におけるクラゲの音響散乱特性を考慮して、日本海において計量魚群探知機を用いてクラゲを探査したが、当該大型クラゲおよびクラゲに集まる他の生物との対応を認めることはできなかった。クラゲの異常発生は、今後、発生する可能性の非常に高い問題であり、本助成が終了した後も、実施する予定である。
• Prediction of short- and long-term stock fluctuations of Japanese common squid, Todarodes pacificus related to climate change

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2007 -2009 

  Author : SAKURAI Yasunori, YAMAMOTO Jun, MORI Ken, KIDOKORO Hideaki, GOTO Tsuneo

   

  We used the new reproductive hypothesis to explain and predict the stock structure or stock fluctuation related to climatic regime shifts and global warming scenario during the 20^-21^ Century. We conclude that short and long-term change of T. pacificus stock can be explained and predicted by physical parameters such as SST, and bottom topography during the spawning period based on this new reproductive hypothesis. Based on this method, we can then monitor the trend of stock fluctuation and structural change such as a seasonal shift of the spawning period related to abrupt changes of the inferred spawning areas. As an example, we present how to monitor the recent seasonal changes of inferred spawning areas and predict the stock condition of the next year cohort. Further, we try to predict the fate of T. pacificus during the 21st Century based on the Global Warning Scenario (IPCC, 2007) using the Earth Simulation System (FRCGC, Frontier Research Center of Global change, Japan). The inferred main spawning grounds still occur from the southern Japan Sea and the East China Sea by 2099. However, the peak of spawning period will shift from October-February in 2005 to November-March in 2050, and December-April in 2099.
• Development of adaptive marine ecosystem management and co-management plan in Shiretoko World Natural Heritage Site : Interaction between land and marine ecosystems

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2006 -2009 

  Author : SAITOH Sei-ichi, KAERIYAMA Masahide, SAKURAI Yasunori, MATSUDA Hiroyuki, WATANUKI Yutaka, MIYASHITA Kazushi, KONO Tokihiro, KUDO Hideaki, HIRAWAKE Toru, SHIOMOTO Akihiro, YAMAMOTO Jun

   

  We carried out the development of monitoring methods on marine life and their environment and promoted various field observations in Shiretoko World Natural Heritage (SWNH) area. As a result, it is clear that there is difference in primary production system between northern coastal region and southern coastal region. We clarified 1) the effect of Pacific salmon (Genus Oncorhynchus) escapement on supply of marine-derived nutrients to the riparian ecosystems using the stable isotope analysis, and 2) to estimate escapement dynamics and spawning carrying capacity of the wild pink salmon (O.gorbusha) relating to the feeding behavioral pattern of brown bear (Ursus arctos) in SWNH area. Based on the adaptive marine ecosystem management, we proposed new method to evaluatean optimum fisheries operation for each fish species using both catch of fish and haul of fish in the Shiretoko coastal fisheries.
• 音響技術を用いた水中映像定量化技術の開発

  日本学術振興会：科学研究費助成事業

  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。
• 発生期で変動パターンが異なるスルメイカ資源変動機構の解明

  日本学術振興会：科学研究費助成事業 若手研究(B)

  Date (from‐to) : 2005 -2007 

  Author : 山本 潤

   

  本研究では,本種の秋および冬発生群の示す資源変動パターンが,"再生産時期の秋から冬にかけての冷却の進行と,経年的な冬季の冷却強度が卵塊・ふ化幼生の生残に影響する"との見地に立ち,スルメイカの資源変動のメカニズムを解明することを目的として実施した.今年度では,これまでのスルメイカの生活史における知見(ふ化幼生の正常遊泳水温範囲,産卵海域の水深,海洋構造との関係)を基に,衛星画像,気象データ,海底地形データより,スルメイカ幼生の生残海域を,地理情報システム(GIS)の手法を用いて,主産卵場である東シナ海における,10月から3月までの当該海域の空間的,時間的な変化を解析した。今年度では,さらに精度を上げるために気象庁が作成した衛星画像再解析データ(MGDSST)を用いた。 その概略は ・東シナ海では,10月から3月にかけて季節風の速度の増加とともに気温が下がり,海面を冷却している。 ・ふ化幼生の生残可能海域は,秋生まれ群が発生する10月から11月までは対馬暖流の影響下の東シナ海の陸棚上にあり,冬生まれ群が発生する1月から3月までは,黒潮が卓越する黒潮の影響下にある。 ・秋生まれ群,冬生まれ群は,対馬暖流と黒潮の二つの輸送経路に分かれるかを解明。 ・結果的に,本種はこの輸送経路の切り替わりによって,生残に不適な生物・物理環境への輸送,索餌,被食などを分散させる,bed-hedging戦略をとっていることが明らかになった。 これからのことから,秋生まれ群は相対的に生産力が低いが変動が小さい日本海へ,冬生まれ群は,変動が生産力は高いが変動の大きな太平洋側へと輸送されることによりその変動パターンが異なることが明らかになった。本成果は只今,国際雑誌に投稿中である。
• Reproduction and Recruitment Success of the Japanese Common Squid, Todarodes pacificus, related to Annual and Seasonal Changes of Winter Wind Stress and Mixed Layer Depth.

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2003 -2005 

  Author : SAKURAI Yasunori, SAITOH Sei-ichi, BOWER John R., YAMAMOTO Jun

   

  Recruitment success in squids depends largely on environmental conditions at the spawning and nursery grounds. The autumn and winter spawning groups of Japanese common squid, Todarodes pacificus have the largest biomass and the annual catch of winter groups have fluctuated widely. T.pacificus produces gelatinous, nearly neutrally buoyant egg masses that contain many small eggs. The egg masses are thought to occur within or above the pycnocline at temperatures suitable for egg development (e.g., 15-23℃ in T.pacificus) and under conditions of reduced predation. After hatching, the paralarvae presumably ascend to the surface layer and are advected into convergent frontal zones We observed something resembling a T.pacificus egg mass within the pycnocline at 70-120 m depth (temperature range : 18-21℃) in the Tsushima Current using an ROV. We also estimated from laboratory studies that hatchlings ascend to the surface at temperatures of 18-23℃. We used this new reproductive hypothesis to estimate winter spawning areas of T.pacificus. Results of a previous study suggested that annual catches of T.pacificus increased during periods of weak winds and warm air temperature, suggesting that the strength of winter winds may affect recruitment. The spawning areas of winter spawning group during warm regime after 1990's were estimated to be along the continental edge off the Kyushu Island and the Nansei Islands. Inner flow of Kuroshio will transport paralarvae in surface layer from the spawning areas to the nursery areas of northeastward along the continental edge. However, the spawning areas during cool regime during 1980's were reduced along the continental edge. We can present a scenario for how stock size in T.pacificus might fluctuate due to environmental factors such as sea surface temperatures and suggest how to forecast the stock fluctuation related to climatic regime shifts and global warming.
• Stock Fluctuations throughout Reproduction and Recruitment Process of the Japanese Common Squid, Todarodes pacificus, related to Climate Changes

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2000 -2002 

  Author : SAKURAI Yasunori, BOWER John R., ISODA Yutaka, SAITOH Sei-ichi, YAMAMOTO Jun

   

  In short-lived squids, recruitment success most likely depends on the physical and biological environments at the spawning and nursery grounds. No egg masses have been observed in the natural habitat. During 2000-2002, MOCNESS and an ROV were used to examine the distribution of egg masses and paralarvae of Todarodes pacificus in the Sea of Japan. Gelatinous egg masses were observed at two stations in the Tsushima Current along the continental shelf off the Oki Islands in November, 2000. They occurred within the pycnocline (75 and 95 m depth, respectively), where temperatures were about 18℃, which was suitable for embryonic development. Upon hatching, paralarvae may rise to the surface layer, where they would be carried into the convergent frontal zone in the Tsushima Current. Annual catches of T. pacificus, have markedly increased since the late 1980s, and recent catches have equaled those of the 1960s. The winter spawning area of T. pacificus in the East China Sea shrank when adult stocks decreased during a cool regime that occurred before 1988, and that its fall and winter spawning areas extended and overlapped in the Sea of Japan and East China Sea when adult stocks increased during a warm regime after 1989. Successful hatching from egg masses was to be higher when the mixed layer depth (MLD)is shallower than the bottom depth. We examined the relationship between annual catch of the winter-spawning stock, and wind speed and air temperature in the East China Sea in February during 1980-2000 to determine how a series of calm and warm winters might promote a stock increase related to changes in the MLD. Annual catches markedly increased during a decade of weak wind speed and warm air temperature from the mid-1980s to mid-1990s, suggesting that the strength of winter wind stress affects the winter-spawning stock fluctuations in T. pacificus.
• Study on the sampling properties of the plankton nets.

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

  Date (from‐to) : 2000 -2002 

  Author : SAKAOKA Keiichiro, YONETA Kunisaburo, SHIGA Naonobu, MEGURO Toshimi, BOWER John, YAMAMOTO Jun

   

  Plankton nets have been used for as a method for collecting the plankton. Especially, the NORPAC-NET is widely used in order to keep the compatibility of the data and there are many long-term data based on the NORPAC samples. NORPAC-NET sampling is easy to operate, the wire angles often exceed 40 degrees when sea condition is rough. These would suggest that these samples were estimated over or less than the normal condition. Then, this study investigates the collection characteristic of the NORPAC net and the property of the long-term data set. Furthermore, the present study examines other plankton net, MTD-Net, Bongo-Net and the retention on the survey-net mesh.
• スルメイカ類幼生の最適生残のための生物・物理環境の検出

  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 : 山本 潤

   

  本研究では、今年度に以下の調査を実施した. 1.1999年11月上旬〜中旬に隠岐諸島周辺海域においてスルメイカ幼生の分布特性調査を実施 2.2000年2月上旬〜中旬にハワイ諸島周辺海域におけるアカイカ類幼生分布調査を実施 1の調査は、鳥取県水産試験場試験船第一鳥取丸を用いて行った。幼生の採集は、多段式プランクトンネットを用いて、0、0-25、25-50、50-75、75-100mの5層について、計14点で実施した。深度別に採集された幼生の分布は、ふ化直後と考えられる外套長1mm未満の幼生が、海表面近くの0-25m層に最も多く出現し、幼生の外套長が大きくなるにつれて、その分布深度が深くなる傾向が認められた。スルメイカの産出卵塊は弱い沈降性を示すことが飼育実験より報告されているが、本調査の結果から、スルメイカ幼生は海表面近くでふ化し、成長するにしたがって下方へと拡散(移動)することを示唆し、産出卵塊が海表面近くに存在した可能性を示していた。本調査結果については、平成12年度日本水産学会春季大会と2000年7月上旬に英国アバディーンで開催される国際頭足類諮問機構で口頭発表する予定である。 2の調査は、北大水産学部練習船北星丸を用いて、ハワイ諸島周辺におけるアカイカ・トビイカ幼生をボンゴネットを用いて採集し、海洋環境と幼生分布との対応を調べた。
• 再生産機構に関わる海洋生物の資源変動解析