NIPPON SUISAN GAKKAISHI
Online ISSN : 1349-998X
Print ISSN : 0021-5392
ISSN-L : 0021-5392
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Volume 73, Issue 6
Displaying 1-32 of 32 articles from this issue
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  • Role of grazing by sea urchins on the persistence of a seaweed bed on a seawall in Osaka Bay; the effect of experimental density manipulation
    YOSHIHIRO YONEDA, TANEMI FUJITA, HIROYUKI NAKAHARA, TETSUHIKO TOYOHARA ...
    2007 Volume 73 Issue 6 Pages 1031-1041
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1031
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      The effect of grazing by sea urchins was monitored in a three-year field experiment (June 2002 to June 2005) on a seaweed community established on a seawall in Osaka Bay. In the experiment, three levels of urchin density were used: one was unmanipulated (control), one from which urchins were removed manually every month (removal), and one to which urchins was added manually to twice that of the unmanipulated one (double density). The seaweed community was composed mainly of perennial red algae, such as Gelidium elegans and Chondrus spp., when the experiment commenced. At the double density of sea urchins, urchin grazing reduced these algae drastically in winter 2003, resulting in formation of large barren patches. A large annual alga, Undaria pinnatifida, occurred at a high density in the patches and flourished in the spring, followed by an increase in the density of large perennial algae, Ecklonia spp. The recruits of Ecklonia spp. grew rapidly from autumn to winter and dominated in biomass though they were damaged by typhoon from summer to autumn 2004. These results suggest that the grazing pressure of sea urchins plays an important role in the development and persistence of the seaweed community in the eutrophic waters.
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  • Vertical distribution survey of the giant jellyfish Nemopilema nomurai by an underwater video camera attached to a midwater trawl net
    NAOTO HONDA, TOSHIHIRO WATANABE
    2007 Volume 73 Issue 6 Pages 1042-1048
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1042
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      Recently, the mass appearance of the giant jellyfish Nemophilema nomurai has caused serious damage to Japanese fisheries. To reduce the damage to fisheries, it is necessary to understand the distribution and behavior of the giant jellyfish in detail. The vertical distribution of the giant jellyfish was investigated using a midwater trawl net with an underwater video camera and depth loggers. The cod end of this midwater trawl net was opened so as not to capture the giant jellyfish, because the giant jellyfish is too huge to capture and its body would easily choke in the mesh of the net. The midwater trawl net was operated at approximately 100 kilometers off the west coast of Noto Peninsula in the Sea of Japan. Almost all giant jellyfishes were in the surface water shallower than approximately 40 meters depth in the daytime.
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  • Large-scale cryopreservation of Japanese pearl oyster Pinctada fucata martensii sperm
    HIDEO AOKI, AKIRA KOMARU, TERUYOSHI NARITA, KIYOSHI ISOWA, MASAHIRO HA ...
    2007 Volume 73 Issue 6 Pages 1049-1056
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1049
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      To develop methods for large-scale cryopreservation of Japanese pearl oyster spermatozoa, post-thaw motility and fertility of spermatozoa cryopreserved in straw and in a flat-bottomed aluminum cup were compared. Spermatozoa diluted 1:19 with an extender comprising 10% methanol, 72% seawater, and 18% fetal bovine serum were placed in the straw (0.25, 1.0, and 2.0 mL) and in the cup (10 mL). The vessels were then cooled in LN vapor to -50°C at a cooling rate of -17.6 to -20.6°C/min, and immersed in LN. The percentages of motility of spermatozoa cryopreserved in 0.25 mL, 1.0 mL, 2 mL straws, and the cup were 35.2%, 31.1%, 23.2%, and 31.8%, respectively, of the pre-cryopreserved spermatozoa. When 100 μL of semen (pre-cryopreserved or cryopreserved in the 3 kinds of straw) was introduced to 2.5 million eggs, the percentages of fertility were invariably high, but not significantly different from one another. When fresh spermatozoa with low motility were cryopreserved, thawed, and then introduced to eggs, the percentage of fertility increased in a time-dependent fashion, until 20 min after the commencement of insemination. There were no harmful effects on growth and feed intake ability of pearl oyster larvae when the contact time of gametes at fertilization had been prolonged from 5 min to 60 min.
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  • Growth of juvenile ayu Plecoglossus altivelis altivelis in the coastal waters off western Kii Peninsula
    YO YOSHIMOTO, HISAYUKI FUJII, HAJIMU NAKANISHI
    2007 Volume 73 Issue 6 Pages 1057-1064
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1057
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      Hatch dates and early growth rates of ayu Plecoglossus altivelis altivelis in the coastal waters of western Kii Peninsula from 1990 to 1997 were estimated by otolith microstructure. Mean growth rates of juvenile ayu hatched in November were significantly positively correlated with plankton biomass in January and negatively correlated with sea surface temperature (SST) in December. Hatch dates of juvenile ayu were distributed in the early spawning season in the northern coastal areas (Yuasa Bay) compared to the southern coastal areas. The mean growth rates of juvenile ayu hatched in November were higher in the northern coastal areas than the southern coastal areas. With the increase of juvenile ayu, the growth rates tend to increase in the Hidaka coastal areas. These results suggested that the stock size of juvenile ayu is associated with plankton biomass, SST and the early growth rates during the winter season in the coastal waters of western Kii Peninsula.
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  • The extent of impact of organic loads from fish farming on chemical characteristics of sediment and macrobenthos communities in the central fish farming area in Tanabe Bay
    TAKASHI UEDE
    2007 Volume 73 Issue 6 Pages 1065-1073
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1065
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      The extent of impact of organic loads from fish farming on chemical characteristics of the sediment and macrobenthos communities was investigated in the central fish farming area in Tanabe Bay. There were no differences in concentrations of AVS, TOC and TN in the sediment and macrobenthic indices regarding distance from fish cages. From these results, the impact of organic loads from fish farming on AVS, TOC, TN and macrobenthos communities is slight. In contrast, decrease in concentrations of TP, and increases in C/P and N/P ratios in the sediment were observed as the distance from the fish cages increased. The increase in TP closer to the fish cages results from the accumulation of Calcium-bound phosphorus originating from feeds of cultured fishes and their feces. From these results, the extent of impact of organic loads concerning the concentrations of TOC and TP in the sediment is within 100 to 200 m from the fish cages.
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  • Geographical difference in body length composition of red tilefish Branchiostegus japonicus in the East China Sea
    HIDEYUKI YAMASHITA
    2007 Volume 73 Issue 6 Pages 1074-1080
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1074
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      Red tilefish Branchiostegus japonicus is the main target species of bottom longline fisheries in the East China Sea. To explore methods of optimizing utilization of the resource by protecting small fish, TL compositions were analyzed using logistic regression analysis. Fishing region, year, season and sex of the species were used for explanatory variables. The model selection by using Akaike's information criterion (AIC) indicated that the best fit model includes all the explanatory variables. The fishing region had the largest effect. Small individuals tend to be distributed in higher abundance in the northeastern and western regions of the continental shelf. The results of the analysis indicate the possibility of a management strategy for protecting small fish by closing fishing regions where small fish are predominant.
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  • Effects of water temperature on survival, development and feeding of larvae of the horsehair crab Erimacrus isenbeckii (Crustacea, Decapoda, Brachyura) reared in the laboratory
    TADAO JINBO, KATSUYUKI HAMASAKI, MASAKAZU ASHIDATE
    2007 Volume 73 Issue 6 Pages 1081-1089
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1081
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      To determine the optimal rearing temperature for the larval horsehair crab Erimacrus isenbeckii, newly hatched larvae were reared in groups of 50 in 2-L beakers, the water temperature in which was regulated to 6, 9, 12, 15, 18, 21°C, respectively. Survival rates of larvae were high in the beakers at 6 to 15°C; however, mass mortality occurred in the beakers at 21°C from the third to fourth zoeal stage and at 18°C from the fifth zoeal stage through megalopa to first crab stage. The number of days required to reach each larval stage decreased with increasing temperature to 15°C. The coefficient of variation of the number of days required to reach the first crab stage was high in the beakers at ≥15°C. Carapace length tended to increase with decreasing temperature. The numbers of prey eaten by larvae were high at 9 to 15°C. We concluded that the optimal rearing temperature range for larvae of the horsehair crab was from 9 to 12°C.
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  • Catch per unit effort of halfbeak Hyporhamphus sajori forecasted from body length of 1-year-old fish and number of recruits of Japanese anchovy Engraulis japonicus in eastern Hiuchi-nada, the central Seto Inland Sea
    MASAYUKI YAMAMOTO
    2007 Volume 73 Issue 6 Pages 1090-1095
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1090
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      For catch forecasts of halfbeak Hyporhamphus sajori, I examined the relationship between catch per unit effort (CPUE: kg day-1 boat-1) of halfbeak and their mean standard length (SL: mm) or the number of recruits of Japanese anchovy Engraulis japonicus in eastern Hiuchi-nada, the Seto Inland Sea. SL in a mixture of normal distributions was estimated with the non-linear least squares method on the length frequency composition. SL in one-year-old males and females ranged from 185.6 to 217.9 and from 194.2 to 228.4, respectively. The catch was mainly composed of one-year-old fish. CPUE fluctuated between 65.1 and 261.1. SL at one year of age was negatively correlated with CPUE. The positive correlation between CPUE and the number of recruits of Japanese anchovy was significant. The multiple regression equation using CPUE (y) as the outcome variable and SL at one year of age of female fish (x1) and the number of recruits of Japanese anchovy (x2: hundred million) as the predictor variable was y=780.82-3.37x1+0.30x2 (y=6, r2=0.98, p<0.01).
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  • The activities of afferent lateral line nerves induced by swimming motions
    KENJI WATANABE, KAZUHIKO ANRAKU
    2007 Volume 73 Issue 6 Pages 1096-1102
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1096
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      Afferent nerve activities of the posterior lateral line in response to sinusoidal dipole stimuli and self-generated stimuli caused by swimming motion were studied. The threshold sensitivity curves in terms of velocity and acceleration indicated that the lateral line of carp has high sensitivity below 200 Hz, suggesting that lateral line response properties are like a low-pass filter. The trunk motions, body bending toward and against the sides of nerve recordings, stimulated the lateral line. The peak of the lateral line nerve responses was obtained almost simultaneous with the increase of velocity and acceleration components of the motions rather than lateral displacement of the trunk. Regression analyses revealed that the intensities of the lateral line responses correlated well with the peak velocities and accelerations. This study is the first demonstration of the relationships between the magnitudes of self-motion and lateral line responses.
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  • Discards in large-scale set net in Tateyama Bay
    SEIJI AKIYAMA
    2007 Volume 73 Issue 6 Pages 1103-1108
    Published: 2007
    Released on J-STAGE: November 26, 2007
    DOIhttps://doi.org/10.2331/suisan.73.1103
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      In order to identify the discards in set net fishery, monthly field surveys were conducted in a large-scale set net in Tateyama Bay, Chiba prefecture in 2005 and 2006. Discards and landings were recorded in weight by species. A total of 35117.7 kg including 174 species were caught in 24 field surveys. Among these, 32158.9 kg including 82 species were landed and 2958.8 kg including 144 species were discarded. CPUE (catch per haul) and DPUE (discards per haul) were 1463.2 kg and 123.3 kg, respectively. The discard rate (DPUE/CPUE) was calculated to be 0.084. The dominant 10 species of discards were anchovy Engraulis japonica, tripodfish Triacanthus biaculeatus, Pacific pomfret Brama japonica, dolphinfish Coryphaena hippurus, cardinalfish Apogon semilineatus, striped catfish Plotosus lineatus, rabbitfish Siganus fuscescens, pitted stingray Dasyatis matsubarai, threeline grunt Parapristipoma trilineatum and stripey Microcanthus strigatus. There was a significant correlation between catch and discards (r=0.84, p<0.05).
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