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Last Updated :2024/09/03

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Master

Affiliation (Master)

  • Faculty of Fisheries Sciences　Marine Bioresource and Environmental Science　Marine Bioresource Science

Affiliation (Master)

  • Faculty of Fisheries Sciences　Marine Bioresource and Environmental Science　Marine Bioresource Science

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Profile and Settings

Profile and Settings

  • Name (Japanese)

    Yamamura

  • Name (Kana)

    Orio

  • Name

    201601009314754922

通称等の別名

    Orio Yamamura

Achievement

Research Areas

  • Environmental science/Agricultural science / Environmental dynamics

Committee Memberships

  • 2021/03 - Today   Editorial board member, Fisheries Oceanography

Published Papers

  • Orio Yamamura, Kouji Kooka
    Journal of Sea Research 195 102418 - 102418 1385-1101 2023/10 [Refereed]
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  • Kosuke Nagano, Orio Yamamura
    FISHERIES RESEARCH 261 0165-7836 2023/05 [Refereed]
     
    We attempted to forecast catches of giant Pacific octopus Enteroctopus dojeini using past catch data and the machine learning approach. The algorithms tested were the Seasonal Autoregressive Integrated Moving Average (SARIMA), Light Gradient Boosting Machine (LightGBM), a type of Gradient Boosting Decision Tree (GBDT), and the Recurrent Neural Network (RNN), the latter of which is represented by Long Short-Term Memory (LSTM) and Gated Recurrent Unit (GRU). The catch of giant Pacific octopus on the southern coast of the Tsugaru Strait was backcasted for 2001-2019, using data of at least 20 years (1981-2018) for training. In this study, a longer training period led to better performance of SARIMA; the model trained from all past years performed better than models trained from the past 20 or 5 years. Moreover, for LightGBM, fishing-season accuracy of the basic L-GBM's was equal to that of L-GBM-T, which adds environmental factors to the explanatory variables. As a result of 19 backcasting trials, the SARIMA model obtained the best agreement with the actual catch data (R2 = 0.848) followed by L-GBM and LSTM (both R2 = 0.847), and GRU (R2 = 0.839). The root mean square error (RMSE) was within a narrow range for all four models (28.5, 28.0, 27.9, and 28.2 metric tons [t] for SARIMA, L-GBM, LSTM, and GRU, respectively). The SARIMA model was unstable when performance was assessed by the mean absolute percentage error (MAPE), which was standardized by average catch per year, whereas LSTM and GRU remained relatively stable. However, the latter two models were difficult to interpret due to their black box-like structures. By contrast, the SARIMA model was advantageous for interpreting the results. LightGBM showed good predictive performance for time-series data, despite being a static model. Thus, each model has advantages and disad-vantages, so it is necessary to choose the best model depending on the purpose.
  • Rongfu Wang, Masayuki Chimura, Kazuhiro Sadayasu, Mitsuhiro Ishino, Orio Yamamura
    MARINE BIOLOGY RESEARCH 18 (7-8) 435 - 447 1745-1000 2022/09 [Refereed]
     
    The ontogenetic and interannual variations in the diet and feeding strategy of Pacific cod (Gadus macrocephalus) were examined based on 1302 specimens collected by a trawling net off the southern coast of Hokkaido from late June to early July during 2016-2020. The diet comprised 63 species (13 taxa). Fish was the most important prey, followed by decapod crustaceans. In 2016, walleye pollock (Gadus chalcogrammus) was the dominant fish prey species, while amphipods, decapods and Japanese lanternfish (Notoscopelus japonicus) were prominent in the diet in 2017. Japanese sardine (Sardinops melanostictus) were more predominant during 2018-2020. An ontogenetic comparison of diet indicated that smaller individuals (<= 400 mm standard length, SL) preyed mainly on small prey items, such as decapod crustaceans and polychaetes, whereas larger individuals (>400 mm SL) preyed mainly on fish. Moreover, prey size exhibited a significant increasing trend with predator body length. These results suggest that Pacific cod has a flexible feeding strategy that differs by life stage. The updated information on predator-prey relationships provided herein improves our understanding of energy flow in the marine ecosystem and could facilitate ecosystem-based fishery management strategies.
  • Saki Maeda, Kenji Sakurai, Tomonari Akamatsu, Ayaka Matsuda, Orio Yamamura, Mari Kobayashi, Takashi Fritz Matsuishi
    PLOS ONE 16 (2) 1932-6203 2021/02 [Refereed]
     
    Bycatch of harbour porpoises (Phocoena phocoena) by gillnets is a recognised threat to populations. To develop effective mitigation measures, understanding the mechanics of bycatch is essential. Previous studies in experimental conditions suggested foraging activity is an important factor influencing porpoises' reaction to gillnets. We acoustically observed the behaviour of wild harbour porpoises around a bottom-gillnet set-up in a commercial fishing ground, especially foraging activity. Passive acoustic event recorders (A-tags) were fixed to the ends of the gillnet, and recorded for 1 392 hours. Although harbour porpoises frequently and repeatedly appeared around the net each day, incidental bycatch occurred only three times during the observations. The stomach contents of two individuals contained mainly Ammodytes sp., which were observable around the bottom-gillnet but not targeted by the fishery. A total of 276 foraging incidents were acoustically detected, and 78.2% of the foraging activity was in the bottom layer (deeper than 25 m). Porpoises appeared around the net with more frequency on the day of a bycatch incident than on the days without bycatch. These results suggest that the harbour porpoises appeared around the bottom-gillnet to forage on fish distributed in the fishing ground, but not captured by this bottom-gillnet. Thus, porpoises face the risk of becoming entangled when foraging near a gillnet, with the probability of bycatch simply increasing with the length of time spent near the net. Bycatch mitigation measures are discussed.
  • Kaoru Hattori, Toshihide Kitakado, Takeomi Isono, Orio Yamamura
    MAMMAL STUDY 46 (1) 3 - 16 1343-4152 2021/01 [Refereed]
     
    Aerial surveys were conducted to estimate the abundance of wintering populations of Steller sea lions (SSLs; Eumetopias jubatus) in the Sea of Japan originated from Russian waters using the line transect sampling method during spring from 2005 to 2019. The survey areas covered the continental shelf off the western coast of Hokkaido. A total of 28 196 km survey effort was made through the study period under suitable sighting conditions. The numbers of SSLs in haul-out sites were counted separately. Estimations and model selection for the effective strip width were carried out using the maximum-likelihood method. The abundance estimates of SSI,s with the line transect method varied annually, ranging from 284 animals (coefficient of variation [Cu] = 0.732) in 2016 to 6271 (CV = 0.194) in 2014. This large variation in abundance estimates might be attributable to interannual changes in the survey coverage, spatial distribution, haul-out behaviors, and seasonal variation of wintering populations of SSLs in the waters off Hokkaido. This warrants further investigation of seasonal and annual change of distribution to adjust key information on the abundance estimates reported here for use in the conservation and management of this species.
  • Sango Nishio, Hiroko Sasaki, Hisatomo Waga, Orio Yamamura
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 181 0967-0645 2020/12 [Refereed]
     
    The structure of demersal fish assemblages was investigated based on a total of 134 trawl samples collected in the northern Bering Sea (NBS) and Chukchi Sea (CS) during 12 summers between 1990 and 2013. In recent years, the timing of sea ice retreat has become earlier in the NBS. The present study was performed to clarify the environmental factors that contribute to the structure of demersal fish assemblages. Walleye pollock Gadus chalcogrammus were numerically dominant, followed by Bering flounder Hippoglossoides robustus and Arctic cod Boreogadus saida. Stations were classified into four major faunal assemblages by cluster analysis based on species density: I) boreal assemblages occurring southeast of St. Lawrence Island; II) stations dominated by Arctic species in the CS; III) stations with mixed Arctic and boreal species southwest of St. Lawrence Island; and IV) a less abundant assemblage limited to the north of Point Hope, comprising Arctic species. A permutation test revealed that, of the four physical parameters considered (i.e., bottom temperature, bottom depth, timing of sea ice retreat (TSR) and timing of sampling), TSR was the most prominent variable; it constituted 19.4% of the overall variance in species density and 57.7% of the variance explained by environmental factors. Multiple regression was applied to further analyze the factors that affected interannual changes in the densities of three zoogeographic types in the NBS. While TSR was the major factor that affected the density of Arctic species, variables that included bottom temperature were important for boreal species. These results suggest that mechanisms associated with sea ice conditions (i.e., annual-scale factors), rather than summer bottom temperature (i.e., short-term factors), influence the distribution of demersal fish assemblages in the NBS and CS.
  • Takeomi Isono, Yumi Kobayashi, Vladimir N. Burkanov, Orio Yamamura
    Wildlife Society Bulletin 1938-5463 2019/06 [Refereed][Not invited]
  • Kouji Kooka, Tomonori Hamatsu, Orio Yamamura
    Marine Biology 165 (6) 0025-3162 2018/06/01 [Refereed][Not invited]
     
    The advective transport of zooplankton provides an important source of energy on continental shelves. On a continental shelf along the Oyashio Current, western subarctic Pacific (42°30′N, 144°00′E), the extant water mass is replaced biannually by inflows of water masses from the highly productive Okhotsk Sea. These inflows and accompanying zooplankton are hypothesized to enhance biological production on the shelf. In this study, seasonal feeding and growth of a juvenile planktivorous fish, walleye pollock (Gadus chalcogrammus), on the shelf were examined in relation to water mass exchanges from September 2003 to June 2005. Zooplankton were sampled from February to April in 2004 and 2005, and in April 2014 and 2015. Juvenile pollock frequently consumed an Arctic copepod, Calanus glacialis, and a boreal euphausiid, Thysanoessa inermis, after January when the shelf was occupied by cold water masses that originated from the southwestern Okhotsk Sea. Juvenile pollock whose diet contained higher contributions of these energy-rich prey items exhibited positive growth in February–March 2005, whereas fish with lower proportions of these prey exhibited little growth during this period in 2004. The winter distributions of the copepod and euphausiid extended from a continental slope area in the southwestern rim of the Okhotsk Sea to the shelf along the Oyashio Current. Together, these results suggest the transport of zooplankton from the Okhotsk Sea likely influences the biological production of the coastal Oyashio ecosystem by enhancing the availability of energy-rich prey for juvenile pollock.
  • Yoko Goto, Akihiko Wada, Noboru Hoshino, Takahiro Takashima, Masaki Mitsuhashi, Kaoru Hattori, Orio Yamamura
    MARINE ECOLOGY-AN EVOLUTIONARY PERSPECTIVE 38 (6) 0173-9565 2017/12 [Refereed][Not invited]
     
    Inter-decadal and geographic variations in the diets of Steller sea lion, Eumetopias jubatus, were examined based on the contents of 408 stomachs collected from coastal areas around Hokkaido Island during the periods 1994-1998 and 2005-2012. The most important prey species in the 1990s were gadid fishes (walleye pollock [Gadus chalcogrammus], Pacific cod [Gadus microcephalus] and saffron cod [Eleginus gracilis]). The frequency of occurrence and gravimetric contribution of gadids decreased in the 2000s latter period at three study sites (Rausu, Shakotan and Rebun) and were replaced by Okhotsk Atka mackerel (Pleurogrammus azonus) and smooth lumpsucker (Aptocyclus ventricosus). However, analysis based on gravimetric composition indicated that the dietary diversity of prey showed only a slight inter-decadal difference, reflecting the wide diversity of prey ingested during both study periods. These results indicate that Steller sea lions along the Hokkaido coast are opportunistic feeders that utilize a wide variety of prey, and appear to feed mainly upon prey that is easily obtained.
  • Matsuda Hiroyuki, Yamamura Orio, Kitakado Toshihide, Kobayashi Yumi, Kobayashi Mari, Hattori Kaoru, Kato Hidehiro
    Therya 6 (2) 283 - 296 2015 [Refereed][Not invited]
  • Tetsuichiro Funamoto, Orio Yamamura, Osamu Shida, Kazuhiko Itaya, Ken Mori, Yoshiaki Hiyama, Yasunori Sakurai
    FISHERIES SCIENCE 80 (2) 117 - 126 0919-9268 2014/03 [Refereed][Not invited]
     
    The Japanese Pacific stock (JPS) and the northern Japan Sea stock (JSS) of walleye pollock Theragra chalcogramma are mainly distributed in the Pacific Ocean and the Sea of Japan off northern Japan, respectively. This paper summarizes and compares the factors affecting the recruitment variability of these two stocks. Spawning season is from December to March for both stocks. JPS recruitment has a positive relationship with the water temperature in January and February, whereas that of JSS has a negative relationship with the water temperature in January, February, and April. One possible reason for this is that pollock larvae have an optimum growth temperature of approximately 5 A degrees C in the field. Drift of early life stages also appears to be an important influence on the recruitment of both stocks. Because the current generated by the northwest wind carries eggs of JPS into the main larval nursery ground, JPS recruitment is enhanced in years when the northwest wind is predominant in February. On the other hand, early life stages of JSS are transported into the nursery ground by the Tsushima Warm Current. However, this current also carries early life stages into the Sea of Okhotsk and offshore, resulting in poor JSS recruitment in years when this current is strong in March. In contrast to JPS, the recruitment of which is significantly impacted by cannibalism, young pollock have not been found in the stomachs of adult JSS. Warm temperatures in the Sea of Japan seem to induce the separation of young and adult pollock, and the shape of the stock-recruitment relationship also suggests that cannibalism is not important for JSS. Based on this knowledge, and on the hatch date distributions of larvae and juveniles, we propose mechanisms that can explain the recruitment fluctuations for JPS and JSS pollock.
  • Orio Yamamura, Tetsuichiro Funamoto, Masayuki Chimura, Satoshi Honda, Tatsuki Oshima
    MARINE ECOLOGY PROGRESS SERIES 491 221 - 234 0171-8630 2013 [Refereed][Not invited]
     
    Interannual variation in the diet of walleye pollock Theragra chalcogramma along the southeastern coast of Hokkaido Island (Doto area) was analyzed using > 15 000 specimens collected in the periods 1989-1992 and 1995-2011, in relation to oceanographic variables. The area experienced a warm period from 1998 to 2002, which was preceded and followed by cold periods. An apparent shift in diet occurred between the first cold period and the warm period. Appendicularians (larvaceans) became an important summer prey for small-sized pollock (<= 300 mm SL) in addition to copepods and euphausiids, which were also important before the onset of the warm period. In medium-and large-sized pollock, an abrupt decrease in mesopelagic fishes (mainly myctophid Diaphus theta) was observed in stomach contents 3 yr after the 1997/1998 climate regime shift, possibly reflecting a recruitment failure of D. theta. Appendicularians, cannibalism and anchovy Engraulis japonica compensated for the disappearance of mesopelagic fishes from the diet. During autumn and winter, a similar shift from micronekton (mainly D. theta and firefly squid Watasenia scintillans) to euphausiids (exclusively Euphausia pacifica) and cannibalism was found between 2000 and 2001. Although diet changes lagged the onset of the warm period, condition factor increased immediately after the regime shift. This inconsistency may be attributable to the bioenergetic response of juvenile pollock, which attain better growth at warmer temperatures. Thus, in the Doto area, the effect of climate variation on the survival of pollock seemed to be limited, due to their flexible feeding behaviors.
  • Tetsuichiro Funamoto, Orio Yamamura, Tokihiro Kono, Tomonori Hamatsu, Akira Nishimura
    FISHERIES OCEANOGRAPHY 22 (3) 193 - 206 1054-6006 2013 [Refereed][Not invited]
     
    Abiotic and biotic factors affecting the recruitment variability of the Japanese Pacific stock (JPS) of walleye pollock (Theragra chalcogramma) were examined using a bivariate regression and multivariate combined model. Of the abiotic variables around Funka Bay (spawning ground), February sea surface temperature (SST) and wind direction index showed significant bivariate relationships with recruitment. February SST was positively related to recruitment, suggesting that warmer water temperature in February favors JPS recruitment. On the other hand, the relationship between February wind direction index and recruitment predicts high JPS recruitment under predominant northwest winds in February. For the biotic variables in the Doto area (nursery ground), significant and negative bivariate relationships with recruitment were observed for catch per unit effort of Kamchatka flounder (Atheresthes evermanni), Pacific cod (Gadus macrocephalus), and walleye pollock, implying an important impact of predation by these groundfishes on JPS recruitment. The overall model incorporating these abiotic and biotic factors successfully reproduced the variability in JPS recruitment. Temperature and wind conditions around the spawning ground along with predator condition in the nursery ground appear to play a dominant role in the recruitment dynamics of JPS. Based on these results and prior knowledge, we propose a new hypothesis to explain the processes controlling JPS recruitment.
  • Kouji Kooka, Orio Yamamura
    ENVIRONMENTAL BIOLOGY OF FISHES 94 (2) 389 - 402 0378-1909 2012/06 [Refereed][Not invited]
     
    Seasonal energy allocation and deficits of marine juvenile fishes have considerable effects on their survival. To explore the winter survival mechanism of marine fishes with low lipid reserves in their early life, juvenile walleye pollock Theragra chalcogramma were collected along the continental shelf of northern Japan over a 2-year period, and energy allocation and deficit patterns were compared between wild and laboratory-starved fish. Contrary to expectations, wild fish generally continued to accumulate protein mass and concurrently tended to reduce lipid mass from late autumn through winter. The most plausible explanation for the continuous structural growth is that juvenile pollock give priority to reducing mortality risk from size-selective predators under quasi-prey-limited conditions. Exceptionally, inshore small fish reduced both constituents during a winter. The inshore fish consumed 2.5 times more lipid energy than protein energy in November-December, but protein was more important than lipids as a source of energy in December-January and in February-March. However, dependence upon protein reserves was lower for the wild fish than for the laboratory-starved fish, suggesting milder nutritional stress of the wild fish than that observed in the starvation experiment. Moreover, the lipid contents of mortalities in the starvation experiment were mostly < 1%, whereas few wild fish had such lipid contents in the field. These results suggest that juvenile pollock are able to avoid both starvation and predation by accumulating protein reserves.
  • O. Yamamura, T. Nobetsu
    JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM 92 (3) 613 - 621 0025-3154 2012/05 [Refereed][Not invited]
     
    Food habits of threadfin hakeling Laemonema longipes, the dominant demersal fish in the upper continental slope of the western sub-Arctic North Pacific, were described based upon >1400 specimens collected off north-eastern Honshu Island and south-eastern Hokkaido Island, Japan. Threadfin hakeling depended exclusively on pelagic organisms including copepods Neocalanus cristatus, Euphausia pacifica, shrimps Sergestes similis, firefly squid Watasenia scintillans and myctophids Diaphus theta. Threadfin hakeling showed a clear size-dependent dietary variation, with mesozooplankton and shrimps being important for small-and medium-sized fish (<= 400 mm standard length (SL)), and myctophids being important for large-sized fish (>400 mm SL). Since all of these prey undertake diurnal vertical migration, it was concluded that threadfin hakeling take an important role in capturing energy and materials transported from the epipelagic zone to the bathypelagic layer over the upper continental slope. Dietary variation among different areas, seasons and depths were also examined. Of these, areal difference was rather obscure reflecting common prey field in the Tohoku and Doto areas under the prevalence of the North Pacific Intermediate Water, whereas clear seasonal difference was found in the Doto area; the 0-group of walleye pollock Theragra chalcogramma was ingested only in the late summer and early autumn in this area.
  • Osamu Sakai, Orio Yamamura, Yasunori Sakurai, Tomonori Azumaya
    ENVIRONMENTAL BIOLOGY OF FISHES 93 (3) 319 - 331 0378-1909 2012/02 [Refereed][Not invited]
     
    Seasonal, ontogenetic, and diel variations in the diets of chum salmon, Oncorhynchus keta, were examined by analyzing the stomach contents of 1398 fish (300-755 mm fork length) collected in the Bering Sea during summer and early autumn of 2002. Whereas mesozooplankton, including euphausiids, hyperiids, and gastropods, constituted the greatest portion of the stomach contents during the summer, forage fishes (Stenobrachius leucopsarus and Atka mackerel, Pleurogrammus monopterygius) were the most important items during early autumn. Although no apparent diel trend was found in feeding intensity, distinct diel differences in prey composition were observed. Chum salmon caught in the morning contained Stenobrachius leucopsarus, whereas those caught in the afternoon had mainly fed on euphausiids. Thus, chum salmon diets change temporally because of changes in prey availability that result from differences in the annual life cycles and diurnal vertical migrations of prey species.
  • Kanako Toge, Rei Yamashita, Kentaro Kazama, Masaaki Fukuwaka, Orio Yamamura, Yutaka Watanuki
    PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 278 (1718) 2584 - 2590 0962-8452 2011/09 [Refereed][Not invited]
     
    Seabirds and large fishes are important top predators in marine ecosystems, but few studies have explored the potential for competition between these groups. This study investigates the relationship between an observed biennial change of pink salmon (Oncorhynchus gorbuscha) biomass in the central Bering Sea (23 times greater in odd-numbered than in even-numbered years) and the body condition and diet of the short-tailed shearwater (Puffinus tenuirostris) that spends the post-breeding season there. Samples were collected with research gill nets over seven summers. Both species feed on krill, small fishes and squid. Although the mean pink salmon catch per unit effort (in mass) over the study region was not related significantly with shearwater's stomach content mass or prey composition, the pink salmon biomass showed a negative and significant relationship with the shearwater's body mass and liver mass (proxies of energy reserve). We interpret these results as evidence that fishes can negatively affect mean prey intake of seabirds if they feed on a shared prey in the pelagic ecosystem.
  • Yuni Nakauchi, Youichi Hayakawa, Masakatsu Fujinoki, Orio Yamamura, Makito Kobayashi, Akihiko Watanabe
    ZOOLOGICAL SCIENCE 28 (6) 438 - 443 0289-0003 2011/06 [Refereed][Not invited]
     
    The dimorphic sperm of Hemilepidotus gilberti, i.e., haploid eusperm and diploid parasperm, have different morphologies corresponding to their own roles in fertilization. To estimate how these specific sperm morphologies were established, we focused on the nuclear morphologies and examined their changing processes in dimorphic spermiogenesis. Electron microscopic observation revealed that, in euspermatids, chromatin condensation first appeared as a mosaic pattern of moderate electrodense material in the peripheral region of the round nucleus. Those materials spread across the whole area to form a uniformly condensed nucleus. Chromatin condensation began similarly in paraspermatids to that in euspermatids. These became localized to one side of a nucleus and further condensed to form strong electrodense chromatin clusters, which are a specific feature of parasperm. From the remodeled nuclei of eusperm and parasperm, we found five and three kinds of sperm-specific basic proteins (SBPs), respectively, substituted to histones. The N-terminus amino acid sequences of the SBPs suggest that, in parasperm, one major SBP and two minor ones were distinct from each other. In eusperm nuclei, two kinds of specific SBPs were detected in addition to the homologs of parasperm SBPs. The specific SBPs had homologous amino acid sequences with huge arginine clusters, and one of them was most dominant among the five kinds of SBPs. The different combinations of SBPs in the eusperm and parasperm may cause a specific pattern of chromatin condensation in the dimorphic sperm nuclei of H. gilberti.
  • Kaoru Hattori, Takeomi Isono, Orio Yamamura
    Nippon Suisan Gakkaishi (Japanese Edition) 77 (1) 126  0021-5392 2011 [Refereed][Not invited]
  • Kentaro Morita, Masa-aki Fukuwaka, Naoki Tanimata, Orio Yamamura
    OIKOS 119 (8) 1265 - 1272 0030-1299 2010/08 [Refereed][Not invited]
     
    Large fish often inhabit colder waters than small fish. Using a simple bioenergetic model, we found that the optimal temperature for growth should decrease with increasing body size. We predicted that this mechanism would produce an ontogenetic change in thermal preference and then tested our predictions with Pacific salmon, Oncorhynchus spp. In a laboratory experiment, the slope of a regression of growth increment on initial size became steeper with increasing temperature, so that the optimal temperature for growth decreased with increasing body size. In field observations, larger and older salmon inhabited cooler areas, whereas smaller and younger salmon inhabited warmer areas. These patterns were consistent with a size-dependent effect of temperature on condition factor, a parameter shown experimentally to be a measure of the most recent growth performance. Temperatures for maximising condition factor were lower for larger fish. Thus, an ontogenetic change in individual thermal preference toward cooler areas maximises the growth performance of fish, and the negative effects of climate warming on growth are hypothesised to be more severe for larger fish.
  • Takeomi Isono, Vladimir N. Burkanov, Noritaka Ueda, Kaoru Hattori, Orio Yamamura
    MARINE MAMMAL SCIENCE 26 (3) 698 - 706 0824-0469 2010/07 [Refereed][Not invited]
  • Masa-aki Fukuwaka, Shunpei Sato, Orio Yamamura, Osamu Sakai, Toru Nagasawa, Akira Nishimura, Tomonori Azumaya
    MARINE ECOLOGY PROGRESS SERIES 403 219 - 230 0171-8630 2010 [Refereed][Not invited]
     
    To provide a key piece of information for understanding the functioning of the Bering Sea pelagic ecosystem, we estimated the biomass of immature chum salmon in the Bering Sea basin in autumn using a return-at-age analysis incorporated with the results of genetic stock identification studies. The estimated biomass was 742 000 t in 2002 and 617 000 t in 2003, which is possibly an underestimate because of the uncertainty of trawl selectivity parameters used in the estimation. Although chum salmon has been the dominant nekton species in the pelagic ecosystem of the Bering Sea basin in recent years, biomass estimates for the species were smaller than one-tenth of the maximum biomass of walleye pollock in the 1980s. Previous studies have highlighted the importance of the huge biomass of mesopelagic planktivores, such as myctophid fishes and gonatid squid, to the ecosystem function of the pelagic Bering Sea. Planktivorous Pacific salmon including chum and pink salmon may also play a significant role as competitors and predators of small planktivores, thus affecting the dynamics of ecosystem function and nekton community structure in the pelagic Bering Sea.
  • K. Hattori, T. Isono, A. Wada, O. Yamamura
    MARINE MAMMAL SCIENCE 25 (4) 949 - 954 0824-0469 2009/10 [Refereed][Not invited]
  • K. Kooka, O. Yamamura, N. Ohkubo, S. Honda
    JOURNAL OF FISH BIOLOGY 75 (1) 186 - 202 0022-1112 2009/07 [Refereed][Not invited]
     
    Seasonal variation in body size and nutritional condition of juvenile walleye pollock Theragra chalcogramma was examined to elucidate the mechanism underlying their first-winter survival on the continental shelf of the Doto area, northern Japan, based on monthly samples collected over 2 years. Stored lipid mass was highest during autumn, but 93% (2004) and 80% (2005) of lipids were exhausted by the onset of winter. Lipid levels in the winter of 2004 remained low (7-14% of the autumnal maximum), and there was reduced growth rate until the spring, whereas in 2005 lipid levels were higher and more variable (10-46% of the maximum) and some growth occurred. An analysis of the allometric relationships between body size and stored energy showed that larger individuals accumulated disproportionately more energy in the autumn, but the advantage disappeared prior to the winter. In January 2004, stored lipid energy was low throughout the Doto continental shelf relative to the continental slope area. These results suggest that winter feeding opportunities on the shelf are severely limited but not completely absent. Previous studies have shown that winter temperatures on the shelf are lower than those in the slope area. It is possible that juvenile T. chalcogramma survive winter on the shelf without a high level of pre-winter lipid storage because the occasional feeding in the cold shelf water benefits energy conservation.
  • Naoki Taniniata, Orio Yamamura, Yasunori Sakurai, Tomonori Azumaya
    JOURNAL OF OCEANOGRAPHY 64 (2) 185 - 194 0916-8370 2008/04 [Refereed][Not invited]
     
    The food habits of the dominant myctophid Stenobrachius leucopsarus were examined in the central basin of the Bering Sea in relation to oceanographic conditions, in summer 2002 and 2003 and spring 2006. S. leucopsarus exhibited an ontogenetic and seasonal dietary shift. In spring, small fish (<= 40 mm) preyed mainly on Neocalanus flemingeri/plumchrus whereas large fish fed mainly on Neocalanus cristatus. In summer, small fish preyed mainly on Metridia pacifica whereas large fish fed mainly on euphausiids (Thysanoessa spp.). In the summer of 2003, when water temperature in the epipelagic layer (<= 100 m) was warmer, reflecting the prevalence of the Alaskan Stream, small-sized S. leucopsarus showed a higher stomach content index, perhaps reflecting the greater abundance of M. pacifica. Thus, the present study shows that the physical variability in the epipelagic layer affects not only diets but also feeding performance of micronekton.
  • Kazuhisa Uchikawa, Orio Yamamura, Tsutomu Hattori
    FISHERIES SCIENCE 74 (1) 69 - 76 0919-9268 2008/02 [Refereed][Not invited]
     
    The feeding habits of Lampanyctus jordani, an abundant mesopelagic fish in the subarctic North Pacific, was examined based on the stomach contents of 721 specimens collected over the continental slope off the Tohoku area, Pacific coast of northern Japan during April and October from 1996 to 1998. The prey items comprised mainly crustaceans such as copepods, amphipods, euphausiids and decapods. Euphausiids were the most important items in the diet both during April and October. During April, when the annual maximum of zooplankton biomass occurred and the Oyashio Intrusion Current prevailed, L. jordani fed intensively and consumed a high proportion of Euphausia pacifica. These seasonal variations also influenced the feeding intensity and dietary diversity. Feeding intensity, measured by the stomach contents index, was higher during April than October, reflecting the higher biomass of zooplankton in the Tohoku area during spring. The dietary diversity of L. jordani was lower during April than October, indicating that L. jordani shifted to a wider variety of prey when the availability of E. pacifica was limited.
  • K. Kooka, O. Yamamura, T. Andoh
    JOURNAL OF FISH BIOLOGY 71 (6) 1714 - 1734 0022-1112 2007/12 [Refereed][Not invited]
     
    The winter energy deficit and mortality of juvenile walleye pollock at extremely cold temperature were examined by field observations and laboratory experiments. In the Doto area, along the northern coast of Japan, juvenile walleye pollock resided on the continental shelf despite extremely cold temperatures (mean 0.4 degrees C) during the latter half of winter (March to April). Measurements of the rate of energy depletion (equivalent to the routine metabolic rate) revealed that juvenile walleye pollock consumed 37% less energy at 0.5 degrees C than at 2.0 degrees C, suggesting an energetic benefit of residence in cold water (< 1.0 degrees C) over the shelf during winter. Prior to the starvation experiments, temperatures and ration level in the holding tanks were adjusted to create two different body condition groups of fish. Under the thermal condition of the latter half of winter (0.5 degrees C), fish with a mean condition factor of 0.6 and 0.5 suffered 19.1 and 74.5% mortality, respectively, at the end of the experiments (after 56 days). The residual analysis of total body energy demonstrated that the cause of mortality was mainly associated with the depletion of energy reserves. When a logistic regression model for mortality derived from the experiments was applied to wild fish collected in March, the estimated overwintering mortality in 2004 and 2005 was 25.4 and < 2.3%, respectively, assuming no feeding during the winter. Considering that juvenile walleye pollock feed during winter as shown in previous studies, intense overwintering mortality induced by energy depletion is improbable during the latter half of winter in the Doto area. (C) 2007 The Authors.
  • Orio Yamamura
    NIPPON SUISAN GAKKAISHI 73 (5) 931 - 932 0021-5392 2007/09 [Refereed][Not invited]
  • K. Kooka, O. Yamamura, A. Nishimura, T. Hamatsu, T. Yanagimoto
    JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 347 (1-2) 69 - 76 0022-0981 2007/08 [Refereed][Not invited]
     
    Food consumption (FC) specific growth rate (SGR), and gross growth efficiency (GGE) were measured for juvenile walleye pollock (initial size 112-153 mm fork length) fed euphausiids at temperatures (T) between 2 and 16 degrees C. FC increased up to 12 degrees C (7.3% of body Nveight) and was slightly lower at 16 degrees C. SGR also increased up to 12 degrees C (2% d(- 1)) but rapidly decreased at 16 degrees C. The optimum temperatures for FC and SGR were 12.3 degrees C and 11.5 degrees C, respectively. GGE was similar (27.3-29.9%) for temperatures in the range of 2-9 degrees C and decreased at higher temperatures. GGE in terms of energy (GGE = - 1.37T + 38.41) and the energy density of fish was higher at lower temperatures, suggesting that residence of juvenile pollock in cold water induces energy storage. In the Doto continental-shelf area, juvenile pollock were distributed over a wide range of temperatures (5.4-15.0 degrees C) during the summer. This suggests that factors other than water temperature may affect the summer distribution of juvenile pollock, although temperature would be the most important factor in a food-unlimited environment. (c) 2007 Elsevier B.V All rights reserved.
  • Michio J. Kishi, Makoto Kashiwai, Daniel M. Ware, Bernard A. Megrey, David L. Eslinger, Francisco E. Werner, Maki Noguchi-Aita, Tomonori Azumaya, Masahiko Fujii, Shinji Hashimoto, Daji Huang, Hitoshi Iizumi, Yukimasa Ishida, Sukyung Kang, Gennady A. Kantakov, Hyun-cheol Kim, Kosei Komatsu, Vadim V. Navrotsky, S. Lan Smith, Kazuaki Tadokoro, Atsushi Tsuda, Orio Yamamura, Yasuhiro Yamanaka, Katsumi Yokouchi, Naoki Yoshie, Jing Zhang, Yury I. Zuenko, Vladimir I. Zvalinsky
    ECOLOGICAL MODELLING 202 (1-2) 12 - 25 0304-3800 2007/03 [Refereed][Not invited]
     
    The PICES CCCC (North Pacific Marine Science Organization, Climate Change and Carrying Capacity program) MODEL Task Team achieved a consensus on the structure of a prototype lower trophic level ecosystem model for the North Pacific Ocean, and named it the North Pacific Ecosystem Model for Understanding Regional Oceanography, "NEMURO". Through an extensive dialog between modelers, plankton biologists and oceanographers, an extensive review was conducted to define NEMURO's process equations and their parameter values for distinct geographic regions. We present in this paper the formulation, structure and governing equations of NEMURO as well as examples to illustrate its behavior. NEMURO has eleven state variables: nitrate, ammonium, small and large phytoplankton biomass, small, large and predatory zooplankton biomass, particulate and dissolved organic nitrogen, particulate silica, and silicic acid concentration. Several applications reported in this issue of Ecological Modelling have successfully used NEMURO, and an extension that includes fish as an additional state variable. Applications include studies of the biogeochemistry of the North Pacific, and variations of its ecosystem's lower trophic levels and two target fish species at regional and basin-scale levels, and on time scales from seasonal to interdecadal. (c) 2006 Elsevier B.V. All rights reserved.
  • O Yamamura
    FISHERIES OCEANOGRAPHY 13 138 - 154 1054-6006 2004/12 [Refereed][Not invited]
     
    An age-structured trophodynamic model was constructed to quantitatively analyze factors affecting post-settlement mortality and growth of walleye pollock (Theragra chalcogramma) in the Doto area, the main nursery ground of the Japan Pacific population. The model included (i) multiple age classes of pollock, (ii) a generic predator, (iii) fisheries, and (iv) major prey of pollock. Major processes considered were (i) recruitment, (ii) bottom-up control of somatic growth, (iii) mortality because of predation, cannibalism and fishing, GO size-selective prey selection, (v) temperature-dependent bioenergetics such as conversion efficiency and daily consumption rate, and (vi) production and advective supply of prey. By assuming that pollock select prey based upon both relative abundance and predator-prey size relationships, the model accurately simulated seasonal and ontogenetic variations in the diet. However considering ontogenetic segregation, the model showed that, due to cannibalism, newly recruited fish would be totally consumed within 6 months after settlement. By considering segregation (10% overlap during spring and 0.1% during other seasons), an agreement of diet between the simulation and empirical data averaged 82.7% for the different seasons and fish sizes. Euphausiids, the most important prey of pollock, suffered the highest predation impact (22.2 +/- 5.3 WWg m(-2) yr(-1)) exceeding annual production in the model domain (17.2 +/- 0.1 WWg m(-2) yr(-1)), indicating that an advective supply of prey is necessary to support the pollock population. The daily ration of pollock during spring and summer averaged at 1.2 and 0.6% BW day(-1) for small (less than or equal to200 mm) and large (>200 mm) pollock, respectively; this daily ration was reduced by half during autumn and winter.
  • S Ito, H Sugisaki, A Tsuda, O Yamamura, K Okuda
    FISHERIES OCEANOGRAPHY 13 1 - 9 1054-6006 2004/12 [Refereed][Not invited]
     
    The comprehensive study of the variation of the oceanic environment and fish populations in the northwestern Pacific (VENFISH) was an interdisciplinary scientific program to enhance our understanding of relationships between the ocean environment and the pelagic fishes, Pacific saury and walleye pollock. As prey of saury and walleye pollock, key species of zooplankton were selected and their life history and production were elucidated. Retrospective analyses were also conducted to investigate the mechanisms of production variation in some zooplankton species. Life history and ecology of Pacific saury and walleye pollock were also investigated and substantial improvements to our understanding of them were achieved. In addition, improved information from VENFISH were used to develop several models to investigate saury growth, and population dynamics, and predatory pressure on zooplankton from walleye pollock. Observational and model results indicate the importance of the Kuroshio and the Kuroshio-Oyashio transition region to saury recruitment and of Oyashio transport to walleye pollock recruitment. Moreover, models developed under VENFISH will become the basis of fisheries management models for saury, walleye pollock, and other fishes in the future.
  • Y Niizuma, O Yamamura
    COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY 139 (1) 97 - 101 1095-6433 2004/09 [Refereed][Not invited]
     
    We investigated the assimilation efficiency (AE) of a piscivorous alcid, Rhinoceros Auklet (Cerorhinca monocerata), chicks when fed Japanese anchovy (Engraulis japonicus) and Japanese sand lance (Ammodytes personatus), which are their main prey species. The assimilation efficiency corrected for nitrogen retention (NR) of the chicks fed sand lance (81.6%) was significantly higher than those fed anchovy (78.0%). The values of assimilation efficiencies for both fish species are similar to those of fish-fed seabird adults and fledglings. (C) 2004 Elsevier Inc. All rights reserved.
  • R Kimura, O Yamamura, Y Oozeki, A Tsuda
    FISHERIES SCIENCE 69 (6) 1209 - 1217 0919-9268 2003/12 [Refereed][Not invited]
     
    We assessed the ability to discriminate local stocks of walleye pollock Theragra chalcogramma based on data from five elements (Na, K, P, Ca and Sr) using electron probe micro analyzer (EPMA) from the otoliths of 26 adult fish (standard length 339-576 mm) caught at four sites (Rausu, Kushiro, Minami-kayabe and Musashi Bank) around Hokkaido, Japan in 1998 and 1999. To compare the elemental compositions, the otolith formation periods were arranged based on the annual rings to allow analysis of comparative winter periods. Elemental concentrations of Na and K remained at a stable level throughout the otolith development. The pattern of Sr concentration differed for each individual. The 1999 winter samples collected from Kushiro, and Minami-kayabe distributed similarly and were discriminated at a near-significant level from samples at Rausu. These results indicate that we might be able to discriminate the local Nemuro and Pacific stocks of walleye pollock spawned around Hokkaido using their otolith elements by comparing portions of otoliths formed in the same year.
  • O Yamamura
    FISHERIES SCIENCE 69 (3) 445 - 455 0919-9268 2003/06 [Refereed][Not invited]
     
    The species composition of demersal fish was studied in nearshore waters (33-116 m depth) of south-eastern Hokkaido, the coldest area around the Japan Archipelago due to the influence of the cold Oyashio Current, using bottom gillnet samples collected during October 1996, August 1997, May 1998 and September 1999. The water temperature just above the sea bottom in the study area was lowest (< 2degreesC) during May and then rose through autumn (>14degreesC). Cottids were the most abundant family in terms of both overall biomass and number, but their gravimetric dominance decreased from May (84%) through October (14%), whereas pleuronectids and stichaeids increased. Of the 57 fish species sampled, plain sculpin Myoxocephalus jaok was the dominant species in terms of overall biomass, accounting for 29.0% of the total biomass, followed by horned sculpin Enophrys diceraus (19.5%), Kamchatka flounder Atheresthes evermanni (6.5%) and blackline prickleback Acantholumpenus mackayi (4.9%). Plain sculpin dominated during May and September, but its predominance was low during October (9.6%), when witch flounder Glyptocephalus stelleri (22.7%) and blackline prickleback (10.8%) became important. This seasonal change appears to reflect the annual life cycle events of the fish, such as spawning.
  • Honda Satoshi, Shida Osamu, Yamamura Orio
    Bulletin on Coastal Oceanography 日本海洋学会 沿岸海洋研究会 41 (1) 39 - 47 1342-2758 2003 [Refereed]
     
    The Japan Pacific population of walleye pollock, which is distributed widely along the Pacific coast of northern Japan, is one of the most important fishery resources in Japanese waters. Spawning of the population occurs in winter adjacent to the mouth of Funka Bay. Pre-settlement juveniles have been found to be migrated from the Funka Bay area to the southeastern coast of Hokkaido (Doto area) via the coast of Hidaka Bay by their first autumn. Thus the Doto area, where they settle and remain for several years, is an important nursery ground for juvenile pollock; they spend 3-5 years while they are immature in the Doto area. By the age of 3 to 5, pollock mature and migrate back to the Funka Bay spawning ground. After spawning, the adults return to the Doto area to recover taking advantage of the high prey abundance. Such a life history capitalizes on the features of the two adjacent areas, the mouth of Funka Bay and the Doto area, as a spawning ground and a feeding ground, respectively.
  • K Uchikawa, O Yamamura, D Kitagawa, Y Sakurai
    FISHERIES SCIENCE 68 (5) 1034 - 1040 0919-9268 2002/10 [Refereed][Not invited]
     
    The diet of Notoscopelus japonicus, one of the dominant mesopelagic fishes in the transitional waters of the western North Pacific, was examined in 106 specimens collected over the continental slope off the Pacific coast of northern Japan during April and October 1996. The prey comprised mainly crustaceans, such as copepods, ostracods, euphausiids and amphipods. Euphausia pacifica was the dominant prey, representing 83.1% by number and 72.4% by wet weight of the total diet. Between April and October, there was no shift in prey species consumed, but prey size decreased significantly and prey number per fish stomach increased in October. These results indicate that, in October, N. japonicus consumed larger numbers of smaller E pacifica, rather than shifting to other prey taxa. The pronounced importance of E pacifica in the diet was ascribed to its co-occurrence with N. japonicus at night in the surface layer and during the daytime in the near-bottom layer.
  • Kazuhisa Uchikawa, Orio Yamamura, Yasunori Sakurai
    海の研究 = Umi no Kenkyu (Oceanography in Japan) 11 (2) 369 - 369 2186-3105 2002/03/05 [Refereed]
     
    北太平洋北西部の亜熱帯域と移行域の中層において個体数で卓越するヨコエソ(Gonostoma gracile)の食性を調べた。試料は1988年6～7月,1995年6月および11月に採集した520個体の標本を用いた。ヨコエソの主要餌生物はカイアシ類,介形類,端脚類およびオキアミ類であった。餌生物の中で数的に最も卓越していたのはカイアシ類と介形類であり,この両者でヨコエソの餌生物のおよそ70%を占めた。ヨコエソの成長に伴う食物ニッチの変化はわずかであり,いずれの魚体長群(19～119mm SL)においても,Pleuromamma属カイアシ類が最も卓越する餌生物であった。利用餌生物のサイズ範囲は大型のヨコエソで広くなるが,いずれの魚体長群においても主として体長1～4mmの餌生物を捕食していた。本種の主要餌生物は生物発光性のカイアシ類と介形類であったことから,ヨコエソは視覚的に餌生物を捕食しているものと考えられる。
  • O Yamamura, S Honda, O Shida, T Hamatsu
    MARINE ECOLOGY PROGRESS SERIES 238 187 - 198 0171-8630 2002 [Refereed][Not invited]
     
    Seasonal, ontogenetic and bathymetric variations of diet were examined for walleye pollock Theragra chalcogramma based on a total of 6666 fish collected off the southeastern coast of Hokkaido Island, northern Japan (Doto area) during 1989 to 2000. Walleye pollock depended exclusively (> 99 %) on pelagic prey and showed a clear ontogenetic dietary shift: smaller fish depended mainly upon mesozooplankton such as Neocalanus cristatus and Euphausia pacifica, and larger fish preyed upon pollock (cannibalism), myctophids Diaphus theta and firefly squid Watasenia scintillans. Seasonal variation was also evident. Smaller pollock depended mainly upon N. cristatus during spring then shifted gradually to E. pacifica during other seasons. For larger pollock, major prey shifted from pollock (cannibalism) during spring to micronekton during other seasons. Bathymetric variation was less pronounced, with cannibalism and Themisto spp. being more important in the shallow area (less than or equal to150 m). Feeding intensity, measured as stomach content index, was generally higher during spring and summer than autumn and winter, but showed incidentally high values during winter, suggesting sporadic but intense feeding opportunities. Fish condition fell during winter and then recovered rapidly during May and June. Recovery coincided with superabundance of N, cristatus during blooming, so that this species is essential for the recovery of pollock from wintering and spawning.
  • O Yamamura, K Yabuki, O Shida, K Watanabe, S Honda
    JOURNAL OF FISH BIOLOGY 59 (3) 645 - 656 0022-1112 2001/09 [Refereed][Not invited]
     
    Cannibalism in walleye pollock off the eastern coast of the Hokkaido Island, Japan was important only during spring (April to June), and its importance increased from 0% in dry mass for < 200 mm L-S fish to 48(.)9% for > 400 mm Ls fish. Most of the prey was represented by age I year fish, showing a unimodal body size distribution with a mode at 121-130 mm. Although cannibal body size was larger in deeper (> 150 m) water, there was no difference in prey size by depth, suggesting impingement of the predators inhabiting deeper water into the shallow areas to cannibalize I year fish. The minimum ratio cannibal: prey size was 1(.)74. There was a positive but non-significant correlation between the contribution of cannibalism to a potenital predator's (> 300 nun) diet and an estimate of the previous year's recruitment. This was due to an extremely high contribution of cannibalism during 1992, when a distinctly larger size of predators seemed to bias the contribution. When the 1992 data were removed from the analysis, a significant correlation was obtained (r(2) = 0(.)77, P < 0(.)01), showing that pollock cannibalism is rather density dependent. Based on the results, it is hypothesized that the 'overflow' of 1 year fish from the shelf waters due to their high abundance and the weak stratification in the spring water column results in increased co-occurrence with adult fish and consequent cannibalism. (C) 2001 The Fisheries Society of the British Isles.
  • Kazuhisa Uchikawa, Orio Yamamura, Yasunori Sakurai
    Journal of Oceanography 57 (5) 509 - 517 0916-8370 2001 [Refereed][Not invited]
     
    The diet of Gonostoma gracile, a numerically abundant mesopelagic fish in the Subtropical Region and the Transition Domain of the northwestern North Pacific, was examined using 520 specimens collected during June-July 1988, June 1995 and November 1995. The prey included mainly copepods, ostracods, amphipods and euphausiids. Copepods and ostracods were the most abundant, comprising approximately 70% of the total diet. There was little evidence of an ontogenetic dietary shift Pleuromamma copepods were the most abundant prey for all size classes of fish ranging from 19 to 116 mm in standard length. The size range of prey increased with growth, but all fish sizes examined fed mainly on 1-4 mm long prey. Luminescent copepods and ostracods were the most abundant prey, suggesting that G. gracile detects its prey visually.
  • O Yamamura, T Inada
    BULLETIN OF MARINE SCIENCE 68 (1) 13 - 25 0007-4977 2001/01 [Refereed][Not invited]
     
    The importance of micronekton as food of demersal fish assemblages over lower continental shelves and upper continental slopes off Sendai Bay, northern Japan was studied based on a total of 256 trawl samples collected during May and November from 1989 to 1992. All of the dominant gadiform fish species, which made up the bulk of the assemblages (Gadus macrocephalus, Theragra chalcogramma, Physiculus maximowiczi and Laemonema longipes) depended on micronekton to some extents, and the dependence was higher for larger individuals and in the deeper regions. Important micronekton species consumed were firefly squid (Watasenia scintillans), sergestiid shrimp (Sergestes similis) and myctophids (Diaphus theta, D. kuroshio, and Lampanyctus jordani). The contribution of micronekton to the total diet of fish assemblages was calculated based on species composition and diets of predators. The contribution was higher in the deep region (>300m for May, >200 m for November) accounting for averages of 37.5 and 37.7%, respectively In the shallow region, there was only slight contribution of micronekton during November due to the prevalence of warm Kuroshio water, although moderate contribution (13.5-34.8%) was found during May. Micronekton were therefore implied to perform the following roles in marine food-webs: transporter, condenser and storage.
  • O Yamamura, T Inada, K Shimazaki
    MARINE BIOLOGY 132 (2) 195 - 208 0025-3162 1998/09 [Refereed][Not invited]
     
    The importance of Euphausia pacifica Hansen to the demersal fish community off Sendai Bay, northern Japan. was studied based on a total of 256 trawl samples collected during May, October and November, from 1989 to 1992. The samples were classified into 16 assemblages according to year, month and depth. The importance of E. pacifica to the total diet of each of the assemblages was measured using an index considering both fish diet and species composition. A total of 24 fish species out of 87 were found to ingest E. pacifica. Of these, Gadus macrocephaus and Theragra chalcogramma had the highest predation impact due to their dominance in the fish assemblages and the high proportion of E. pacifica in their diets. The contribution of E. pacifica to the total diet of the fish assemblage was highest in the shallow (less than or equal to 300 m) regions during May, accounting for an average of 38.5% for the 4 years. However, during May 1990, when the warm Kuroshio Extension prevailed, the contribution was higher in the deep (>300 m; 22.6%) region, reflecting active and/or passive movements of E. pacifica. The average predation impact was maximal in the May/shallow assemblage (mean +/- SE; 4.6 +/- 1.4 kg wet wt km(2) d(-1)) and was minimal in the November/shallow assemblage (0.4 +/- 0.3). Annual estimates of consumption by demersal fish fishes ranged from 43 to 128 metric tons, representing 15 to 64% of the annual commercial catch of E. pacifica by local fisheries. It is therefore suggested that the fisheries on E. pacifica have the potential to considerably impact the demersal fish assemblages.
  • O Yamamura
    JOURNAL OF FISH BIOLOGY 50 (5) 919 - 925 0022-1112 1997/05 [Refereed][Not invited]
     
    Pacific saury Cololabis saira were found in 24 out of 1314 stomachs of demersal fishes collected by bottom trawling at 245-393 m depths. The same area was occupied by the stick-held dipnet fishery for saury, in which a landing limitation was enforced to avoid overfishing. The fish species containing saury were: Pacific cod Gadus macrocephalus, walleye pollock Theragra chalcogramma, and oilfish Ruvettus pretiosus. These demersal species would not encounter living saury naturally, which normally are distributed above thermoclines. The ingested saury were smaller than market size which suggests that the saury from fish stomachs were discarded by fishermen because of small sizes to maximize profits under the landing limitation. The scavenged saury made up 41.5, 24.6 and 77.7% of the diets of large-sized (>30 cm) Pacific cod, walleye pollock and oilfish, respectively in terms of DW composition. The extent to which discarded saury contributed to the total diet in the demersal fish assemblage, calculated by considering species composition and diets of bottom fishes, was 21.8% of the total diet. The discarded saury seemed to compensate the less productive feeding environment during autumn for the bottom fishes. (C) 1997 The Fisheries Society of the British Isles.

MISC

Association Memberships

  • JAPANESE SOCIETY OF FISHERIES OCEANOGRAPHY   THE OCEANOGRAPHIC SOCIETY OF JAPAN   THE JAPANESE SOCIETY OF FISHERIES SCIENCE   日本哺乳類学会   

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2020/04 -2023/03 
    Author : 三谷 曜子, 山村 織生, 綿貫 豊, 山口 篤, 中村 知裕
     
    2020年6月に予定していた調査がCOVIDで中止になったため，2021年5月に観光船をチャーターし，調査を実施した．また，2019年度に実施したおしょろ丸調査のデータ解析を進めた．目視調査で最も多く記録された海鳥はハシボソミズナギドリであった（6月29日知床岬沖で65,000羽）．鯨類では，イシイルカ，シャチ，マッコウクジラ，ミンククジラが知床半島の東西で見られたが，ナガスクジラは西側のみで見られた．音響調査により，プランクトンの反応を示す120 kHzの周波数では，能取岬沖と知床半島周辺の東西で大きな反応が見られた一方，魚類の反応を示す38 kHzの周波数では知床半島東側に大きな反応が見られた．CTD-LADCPとXBT観測からオホーツク海沿岸は宗谷暖流水が分布し，根室海峡北部にも海面から水深150dbar付近まで，既に入り込んでいることが明らかになった．また，植物プランクトンの優占分類群では，宗谷暖流が卓越する沿岸域および中冷水では珪藻類，沖合域ではナノ鞭毛藻類と，海域により異なっていた．このような海域差は，水塊間の栄養塩および鉄濃度の違いに起因すると考えられた．動物プランクトンバイオマスには，中型動物プランクトンのカイアシ類Metridia okhotensisが優占し，この種の排泄する糞粒が鉛直的な物質輸送に大きく貢献することが示された．11地点で実施したMOHTネットによる採集では，斜里沖陸棚斜面上部の2地点（B2およびB3）でソコイワシ科に属する魚類マイクロネクトンのまとまった採集がみられた．しかし，両地点は必ずしも鯨類や海鳥類との高密度域とは一致しておらず，これら高次捕食者の分布との関連が薄い可能性が示された．

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