NIPPON SUISAN GAKKAISHI
Online ISSN : 1349-998X
Print ISSN : 0021-5392
ISSN-L : 0021-5392
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Volume 80, Issue 2
Displaying 1-45 of 45 articles from this issue
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Foreword
Originals
  • Net efficiency of a bottom trawl survey for snow crab Chionoecetes opilio off the Pacific coast of northern Honshu, Japan
    TSUTOMU HATTORI, MASAKI ITO, YASUTOKI SHIBATA, TOSHIKAZU YANO, YOJI NA ...
    2014 Volume 80 Issue 2 Pages 178-184
    Published: 2014
    Released on J-STAGE: March 20, 2014
    DOIhttps://doi.org/10.2331/suisan.80.178
    JOURNAL FREE ACCESS
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      When estimating biomass by the area-swept method of bottom trawl surveys, it is important for fisheries managers to estimate the change in capturing efficiency of the net (Q) with the body size of a target species. In this study, Q depending upon the foot rope of a bottom-trawl net was examined for snow crab Chionoecetes opilio using an experimental trawl net (a normal trawl net equipped with an auxiliary net underneath) off the Pacific coast of northern Honshu, Japan. The relationship between carapace width (CW) and Q was expressed by a logistic equation using a generalized linear mixed model (GLMM) because Q increased with CW. The model without the effect of “sex” was selected as the best one by AIC (Akaike's Information Criterion). The maximum value of Q determined by the equation reached 0.664, suggesting that more than 50% of snow crab with CW of over 70 mm were caught by bottom trawl. The CW-Q relationship should be used for estimating the biomass of snow crab in the trawl survey, because the biomass of smaller/larger crab tends to be under-/over-estimated when a constant value of Q is used.
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  • Seasonal changes in the testis of the North Pacific common minke whale
    SATOKO INOUE, TOSHIYA KISHIRO, YOSHIHIRO FUJISE, GEN NAKAMURA, HIDEHIR ...
    2014 Volume 80 Issue 2 Pages 185-190
    Published: 2014
    Released on J-STAGE: March 20, 2014
    DOIhttps://doi.org/10.2331/suisan.80.185
    JOURNAL FREE ACCESS
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      Seasonal changes in the testis of the common minke whale in the North Pacific from April to October were analyzed. Testis weight was analyzed in 268 individuals, 70 of which (10 per month) underwent histological examination. An increase in testis weight was observed in only individuals with body length greater than 7 m and only after July. Expansion of seminiferous tubule diameter was detected after a reduction in diameter observed from May to June. Spermatocytes, which are developed germ cells, were most decreased in July and increased thereafter. These results suggest that the spermatogenetic activity of the common minke whale has seasonal changes, namely, that it reduces from May to June and is activated in August in preparation for the next breeding season.
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  • Effects of spawning time on the variation of vertebral number in chum salmon Oncorhynchus keta
    DAISEI ANDO, YOSHIHITO SHINRIKI, KAZUTAKA SHIMODA, RYOHEI YASUTOMI, YO ...
    2014 Volume 80 Issue 2 Pages 191-200
    Published: 2014
    Released on J-STAGE: March 20, 2014
    DOIhttps://doi.org/10.2331/suisan.80.191
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      We investigated the relationship between vertebral number variations and spawning time of chum salmon Oncorhynchus keta in the Chitose- and Izari Rivers, Hokkaido Island, Japan. The means of vertebral number in early-spawning populations were higher than those of late-spawning populations in both rivers. A similar trend was observed in juveniles that were derived from different spawning groups in the Chitose River and reared under common conditions. In addition, the means of vertebral number in chum salmon fry captured in the early-sampling season (January and February) were higher than those of the late-sampling season (April) in the Izari River. These results suggest that variations of vertebral number in chum salmon adults and fry are affected by spawning time, and that the variations are originally caused by genetic factors.
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  • The grazing of Eisenia bicyclis and several species of Sargassaceous and Cystoseiraceous seaweeds by Siganus fuscescens in relation to the differences of species composition of their seaweed beds
    MIKIO NODA, HIROFUMI OHARA, NOBORU MURASE, ITARU IKEDA, KEN-ICHI YAMAM ...
    2014 Volume 80 Issue 2 Pages 201-213
    Published: 2014
    Released on J-STAGE: March 20, 2014
    DOIhttps://doi.org/10.2331/suisan.80.201
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      We investigated the annual grazing of tagged thalli of Eisenia bicyclis, Sargassum ringgoldianum subsp. coreanum and Myagropsis myagroides and random-selected thalli of several Sargassum species by Siganus fuscescens in a Sargassum bed including a mixed-stand of E. bicyclis and S. ringgoldianum subsp. coreanum and in a mono-specific bed of E. bicyclis. E. bicyclis in the mixed-stand was only slightly grazed, whereas S. ringgoldianum subsp. coreanum was so heavily grazed that almost all of its branches and blades were lost in December. In contrast, E. bicyclis in its mono-specific bed had fish bite scars on its blades in July and about twenty percent of the tagged thalli lost almost all of the blades in November. M. myagroides had fish bite scars on its thalli in August and lost most of its thalli in November. In contrast, S. siliquastrum was only slightly grazed and showed noticeable growth of its thalli in November. Thus, the grazing greatly changed according to the feeding preference of large brown macroalgae and the differences of species composition of their seaweed beds.
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  • Information flow of infection with Ostreid herpesvirus 1 micro variant (OsHV-1 μVar)
    NANAE TAKAGISHI, TOMOYOSHI YOSHINAGA
    2014 Volume 80 Issue 2 Pages 214-221
    Published: 2014
    Released on J-STAGE: March 20, 2014
    DOIhttps://doi.org/10.2331/suisan.80.214
    JOURNAL FREE ACCESS
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      Outbreaks of infection with Ostreid herpesvirus 1 micro variant (OsHV-1 μVar) causing mortalities in Pacific oyster were reported from Europe and Oceania. The Ministry of Agriculture, Forestry and Fisheries issued warnings of the disease to prefectural fisheries divisions and requested them to give the warnings to people and organizations concerned. However, the flow of the warnings was not investigated and it was unclear whether the warnings were actually received by those concerned. We investigated the flow of the warnings by interviews and questionnaire, and found that the warnings were mainly issued to oyster farmers via fisheries cooperatives and that only 30% of oyster farmers knew about the disease. The low rate of oyster farmers with knowledge on the disease seemed to be because some fisheries cooperatives did not relay the warnings to farmers and because not all of the farmers receiving the warnings could understand the risk of this disease probably due to their lack of general knowledge on epidemics of oysters and other mollusks.
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  • The role of environmental factors in the population dynamics of the harmful diatom Asteroplanus karianus in the Ariake Sea, off Saga Prefecture, Japan
    TADASHI MATSUBARA, KAZUNARI YOKOO, YOSHIO KAWAMURA
    2014 Volume 80 Issue 2 Pages 222-232
    Published: 2014
    Released on J-STAGE: March 20, 2014
    DOIhttps://doi.org/10.2331/suisan.80.222
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      Asteroplanus karianus is a harmful diatom and a causative organism in the bleaching of cultured nori (Pyropia). The relationship between the population dynamics of A. karianus and environmental factors was investigated in the Ariake Sea, off Saga Prefecture, Japan. Phytoplankton composition and relevant environmental variables were recorded from December 2007 to March 2012. In addition, the growth and germination of A. karianus under high water temperature and low water temperature conditions were studied in the laboratory. The field study indicated that A. karianus caused red tides only in winter. Nonetheless, laboratory studies indicated that the growth rate of A. karianus was higher under high water temperature conditions than low water temperature conditions. Conversely, the results suggested that the time required for germination of resting stage cells of A. karianus, in bottom sediment was shorter under low water temperature conditions.
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  • Genetic evaluation of reintroduced amago salmon Oncorhynchus masou ishikawae
    HISAE MIYAHARA, HIDEYUKI YAMADA, TAKUYA SATO, YASUSHI HARADA, KOUICHI ...
    2014 Volume 80 Issue 2 Pages 233-240
    Published: 2014
    Released on J-STAGE: March 20, 2014
    DOIhttps://doi.org/10.2331/suisan.80.233
    JOURNAL FREE ACCESS
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      Population revival of amago salmon Oncorhynchus masou ishikawae was attempted by reintroducing wild individuals to an isolated tributary, in which this species had once become extinct, from a neighboring tributary in the same drainage basin, and its effects were evaluated by genetic analyses with nine microsatellite markers. The number of transplants steadily increased, approximately reaching a plateau of population size two years after reintroduction. Although the revived population kept almost the same level of heterozygosity and relatedness as its founding population, the richness of alleles, especially rare alleles, has declined slightly. These results show that, in stream-dwelling fish such as amago salmon, exchange of individuals among neighboring populations in the same drainage basin is important for the long-term preservation of genetic characteristics including genetic diversity, although population revival within a short period is possible by transplanting a small number of parental fish.
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Symposium
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Abstracts of Original Papers
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