NIPPON SUISAN GAKKAISHI

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The origin of sedimentary organic matter in Chita Bay

YUGO MITO, YOSHIHIRO YAMADA, TOSHIYA YAMAMOTO, SACHI NAKASHIMA, AKIKO ...

2007 Volume 73 Issue 1 Pages 1-7
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.1

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The total organic carbon (TOC) content and the carbon stable isotope ratio (δ¹³C) of Chita Bay surface sediments were measured to investigate the organic matter content and origin. Judging from the δ¹³C, the TOC content of the sediments at the western and central parts of Chita Bay were high due to the organic matter originating in the coastal sea. However, we found a large variation in the TOC content and the δ¹³C in the Yahagi River mouth sediments, which suggested that surface sediment organic matter in these areas had different sources from land or coastal sea. Particularly, at the western and central part of the Yahagi River mouth, the TOC content of the sediments was high, and the surface sediment was composed largely of terrestrial organic matter and smaller size particles (<250 μm). These facts suggest that many small particles and organic matter from the Yahagi River will affect the sediment chemical environmental condition in the Yahagi River mouth.

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Bycatch exclusion of snow crab using separator panel in seine net for flounder fishery off Kyoto prefecture

TOSHIAKI MIYAJIMA, ATSUSHI IWAO, NAOKI YAGISHITA, ATSUSHI YAMASAKI

2007 Volume 73 Issue 1 Pages 8-17
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.8

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A seine net with sorting panel and separator panel (mesh size: 600 mm) off Kyoto Prefecture was newly designed to retain flathead flounder Hippoglossoides dubius and Korean flounder Glyptocephalus stelleri, and to release snow crab Chionoecetes opilio during towing. The separator panel was used to exclude snow crab from the catch, where the height of the panel should be kept high for good performance. The proportion of snow crab released out of the net was 74-98%, while catches of flathead flounder and Korean flounder were 67-88% and 57-70%, respectively. The panel allows snow crabs of carapace width smaller than 100 mm to be excluded from the net, and therefore is useful for the conservation of snow crab resources.

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Population dynamics of mantis shrimp Oratosquilla oratoria in Ise Bay, central Japan

TERUYOSHI NARITA, MONTHON GANMANEE, HIDEO SEKIGUCHI

2007 Volume 73 Issue 1 Pages 18-31
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.18

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The present study deals with seasonal and interannual variations in abundance, biomass and spatio-temporal distributions of the mantis shrimp Oratosquilla oratoria in Ise Bay, central Japan. The abundance and biomass of the mantis shrimp decreased in summer when oxygen-poor water developed in the central to inner parts of the bay, and then increased due to new recruits from autumn to spring of the following year when the oxygen-poor water disappeared. Planktonic larvae appeared from June to November, whereas two cohorts were detected for new recruits: one in summer (“summer” cohort) and the other in autumn (“autumn” cohort), respectively. Usually the “summer” cohort grew to 50 mm BL by autumn and became a target for fisheries. This “summer” cohort largely contributed to establishing and maintaining benthic populations of the mantis shrimp in the bay.

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Occurrence of the toxic dinoflagellate Gymnodinium catenatum, toxin contents of suspended matter and prediction of PSP outbreak in the scallop Chlamys nobilis in Inokushi Bay, Oita Prefecture

KAZUYOSHI MIYAMURA, YUKIHIKO MATSUYAMA, SEOK JIN OH

2007 Volume 73 Issue 1 Pages 32-42
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.32

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Since 1996 blooms of the toxic dinoflagellate Gymnodinium catenatum Graham in Inokushi Bay and adjacent areas have recurrently caused paralytic shellfish poisoning (PSP) in the scallop Chlamys nobilis. Weekly plankton monitoring, toxin determination on natural suspended matter and toxicity of C. nobilis were investigated from December 2002 through April 2003 at a station in Inokushi Bay. Direct measurements of natural suspended matter showed that the cell density and estimated toxin content per cell of G. catenatum ranged for 17-8,442 cells L^-1 and 89-1,688 f molcell^-1, respectively. Overall, the toxicity of C. nobilis (digestive gland) rapidly increased with increasing cell density and toxin content in suspended matter. The maximum toxicity of C. nobilis was 675 MU g^-1 on 31 March 2003. Rapid toxin accumulation in C. nobilis was closely related to not only the cell density of G. catenatum but also the increase in the toxin content of G. catenatum. We have succeeded in predicting C. nobilis toxicity (r=0.98), by applying two factors: toxin content in suspended matter and toxin content per G. catenatum cell.

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A simulation model for enhancement and management strategies of fisheries resources: A case study of Japanese Spanish mackerel Scomberomorus niphonius in the eastern Seto Inland Sea

YASUHIRO OBATA, AYUKO TAKIMOTO, AKIO IWAMOTO, SHUICHI KITADA

2007 Volume 73 Issue 1 Pages 43-50
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.43

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A simple population dynamics model that accounts for variation in natural recruitment was developed to simulate the effects of hatchery releases and fishing regulation on fishery resources. We applied this model to the stock recovery plan for Japanese Spanish mackerel Scomberomorus niphonius in the eastern Seto Inland Sea and evaluated the probabilities of various scenarios for achieving the goal of the stock recovery plan. For the scenario of no regulation with zero release, the success probability for achieving the goal was estimated at 63.4%. Conversely, for the scenario of prohibiting autumn fishing targeting 0-year-old mackerel with the release of 50,000 juveniles, the success probability was estimated at 99.3%. The model was also applied to scenarios of fisheries management based on ABC (Allowable Biological Catch) proposed by the Fisheries Agency of Japan, and stock sizes and catches until 2030 were predicted.

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The efficacy of immersion-vaccination against gliding bacterial disease in red sea bream Pagrus major

FUMIHITO KATO, KATSUYA ISHIMARU, OSAMU MURATA, HIDEMI KUMAI

2007 Volume 73 Issue 1 Pages 51-54
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.51

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The efficacy of immersion-vaccination against gliding bacterial disease in red sea bream Pagrus major was examined with formalin killed cells (FKC) of Tenacibaculum maritimum. FKC was prepared from T. maritimum type strain R2 grown on modified Cytophaga agar medium containing 70% sea water for 24 h at 25°C by inactivating with 1.5% (v/v) formalin-PBS for 24 h at 4°C. In experiment I, juvenile red sea bream immersion-vaccinated with FKC (20 μg/mL) for 30 min were challenged with T. maritimum R2 3 days, 1 and 2 weeks after vaccination. The survival rates of the groups challenged after 1 or 2 weeks were significantly higher than those of the control group (P<0.05). In experiment II, a twice-vaccinated group was compared with once-vaccinated groups and control. The survival rates of all the vaccinated groups were significantly higher than that of the control (P<0.05), and the twice-vaccinated group showed the highest survival rate.

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A comparison of survival rates until recruitment for hatchery-released Japanese Spanish mackerel Scomberomorus niphonius with different sizes at release

YASUHIRO OBATA, HIDEKI YAMAZAKI, HIROMASA TAKEMORI, AKIO IWAMOTO, SHIG ...

2007 Volume 73 Issue 1 Pages 55-61
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.55

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Efficiency of recruitment of hatchery-reared juvenile Japanese Spanish mackerel Scomberomorus niphonius was evaluated based on estimates of the survival rate after release. Experiments of juvenile release were carried out in 2002 and 2003 to compare the survival rates of 40 mm juveniles released directly from the production tank with those releases after rearing in net cages in the sea up to 100 mm in total length. The ratio of survival rates of the 2 groups was estimated at 4.10 for 2002 and 3.13 for 2003. Recruitment to the wild population was more efficient in the 100 mm juvenile release than in the 40 mm juvenile release in terms of the production costs and survival after release.

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Chemical characteristics and forms of phosphorus compounds in sediment of fish farming areas

TAKASHI UEDE

2007 Volume 73 Issue 1 Pages 62-68
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.62

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This study is compared the sediment quality of fish farming areas with those of non fish farming ones, to clarify the environmental characteristics of the sediment in fish farming areas. For chemical oxygen demand, total organic carbon, total nitrogen and C/N, no difference was observed between fish farming areas and non fish farming areas. In contrast, total phosphorus concentrations in fish farming areas were higher than those of non fish farming areas. C/P and N/P were lower than those of non fish farming areas. These results caused by the accumulation of Ca-bound phosphorus to the sediment. Concentrations of Ca-bound phosphorus, which originates from fish feed and feces, reached more than 1 mg g^-1 in the sediment of fish farming areas. These findings reveal that determination of phosphorus compounds in the sediment enables us to show the area affected by the organic loads of fish farming.

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Transportation of live squids using sedative effect of magnesium ion, with special reference to the quality difference from frozen and chilled samples

YASUHIRO FUNATSU, KEN-ICHI KAWASAKI, KAZUSHIGE USUI, HISASHI NAKATEGAW ...

2007 Volume 73 Issue 1 Pages 69-77
Published: 2007
Released on J-STAGE: February 06, 2007

DOIhttps://doi.org/10.2331/suisan.73.69

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Live spear squid and Japanese common squid were sedated in seawater containing 20 mM MgSO₄ (Mg-SW). For sedation, seawater temperature was slowly reduced from 15 to 7°C with ice bags. After sedation, live spear squid and Japanese common squid were individually accommodated in a highly gas impermeable plastic bag with 0.6 and 1.0 L of Mg-SW, respectively, and the bags were filled with oxygen and sealed tightly. They were transported at 5°C taking about 27 h by truck. For comparison, samples quickly frozen in liquid nitrogen and instantly killed samples were also transported at -20°C and 5°C, respectively. Changes in various components were measured. Arginine phosphate and ATP contents decreased greatly by transportation in sedated Japanese common squid. There was no clear difference in sensory scores between sedated and chilled Japanese common squid. However, arginine phosphate and ATP contents did not decrease by transportation for spear squid. The mantle muscles of sedated spear squid were more transparent and had a more favorable texture than chilled or frozen samples.

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