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Kato S.,Toyohashi University of Technology | Okabe T.,Toyohashi University of Technology | Aoki Y.,Toyohashi University of Technology | Kamohara S.,Aichi Fisheries Research Institute
Proceedings of the Coastal Engineering Conference | Year: 2014

The color sand tracing to investigate the characteristics of sand movement on the tidal flat (Rokujo-gata in Mikawa Bay, Japan) was conducted in the winter season. Field measurements of currents and water level were also conducted on the flat to grasp the driving factors of currents and sand movement. Currents on Rokujo-gata were affected by wind in alongshore direction which is the north-south direction, and by a tidal oscillation in cross-shore direction. In the winter season, the southward currents are dominant. However the strong northward currents are occasionally generated. It is supposed that these strong currents move sand actively on the tidal flat. The color sand was placed on Rokujo-gata. The sand tracing was conducted during 6 months by sand sampling at 18 locations in the tidal flat and color sand grain counting was also conducted. The color sand was scattered soon after the placement. However it was demonstrated that the color sand remained on the tidal flat even after 6 months. Source


Suzuki K.S.,Japan Central Research Institute of Electric Power Industry | Yasuda A.,Ocean Planning Co. | Yasuda A.,Tokai Marinos Technology Co. | Murata Y.,Ocean Planning Co. | And 6 more authors.
Hydrobiologia | Year: 2015

Blooms of moon jellyfish Aurelia aurita s.l. occur in various vertical distribution patterns within the water column. Reasons for these distribution patterns have remained obscure. To quantify the influence of pycnocline and low dissolved oxygen (DO) on the vertical distribution of A. aurita aggregations, we investigated temperature, salinity, DO, and observed densities of A. aurita at 1–2 m depth intervals via video camera in a eutrophicated, enclosed bay, Mikawa Bay, Japan, for 3 years. During the observed period, stratification and hypoxic status of the bay varied seasonally and interannually due to climatic events, such as rainy season and typhoon passage. Both sharp pycnocline and low DO limited A. aurita vertical distribution. The more strongly stratified the water column, the more the upper boundary of A. aurita distribution was restricted. Bottom hypoxic water limited the lower boundary of A. aurita distribution. The DO threshold for in situ distribution was estimated to be ~2.5 mg l−1, which is much higher than the experimentally obtained, sublethal values identified in previous studies. Our results show that climatic events affect A. aurita vertical distribution through changes in the physical characteristics of the water column. © 2015 Springer International Publishing Switzerland Source


Katayama S.,Tohoku University | Akiyama S.,Tokyo University of Marine Science and Technology | Shimomura Y.,Tokyo University of Marine Science and Technology | Shimomura Y.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Kurogi H.,Aichi Fisheries Research Institute
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2015

Ages of the eels Conger japonicus (n?189) and C. erebennus (n?448) in Tokyo Bay were determined by otolith sectioning. The estimated age range of C. japonicus specimens was 1? to 6? yr (modal range 2? to 4? yr), and of C. erebennus 0? to 11? yr (modal range 5? to 8? yr). Many C. erebennus taken measured over 1000 mm in total length and were more than 6? yr. C. erebennus is therefore characterized as a large-sized eel in comparison with C. myriaster, for which size, age estimations and growth patterns are well documented. Males of C. japonicus and C. erebennus accounted for 2-6% of the specimens sampled in this study, suggesting that the population in Tokyo Bay is composed predominantly of females. Source


Toyokawa M.,Japan National Research Institute of Fisheries Science | Toyokawa M.,Seikai National Fisheries Research Institute | Aoki K.,Yokohama National University | Yamada S.,Aichi Fisheries Research Institute | And 3 more authors.
Journal of Oceanography | Year: 2011

We surveyed the distribution of colonies of polyps of Aureliaaurita sensu lato (s.l.) in Mikawa Bay, Japan. First, we surveyed the distribution of ephyrae of A. aurita s.l. at 75 stations encompassing the whole of Mikawa Bay in early 2008. A total of 37 ephyrae were sampled mostly from fishing ports. Ephyrae were most abundant around the islands located near the mouth of the bay, and decreased from the western part to the eastern part of Mikawa Bay. Next, we selected five fishing ports in Mikawa Bay where ephyrae occurred and surveyed the underside of floating piers and underwater overhangs of wharfs. We found dense colonies of polyps of A. aurita s. l. under nearly all of the floating piers at the two islands located near the mouth of the bay. Fitting a logistic regression model to the dataset showed that the percentage coverage of Aurelia polyps was significantly greater at the two islands compared with the other locations. In addition, the coverage of Aurelia polyps was greater when the coverage of other fouling organisms was in the range of 65-90%, and the coverage of Aurelia polyps was lower on floating piers with a vinyl surface and on concrete wharfs. The combined distribution of polyp colonies of A. aurita s.l. in Ise Bay and Mikawa Bay suggested that A. aurita s.l. in the two bays probably forms a single population and shoals of medusae mainly originate from protected harbors along the mouth-part of the bays. © 2011 The Oceanographic Society of Japan and Springer. Source


Matsumoto T.,National Research Institute of Aquaculture | Awaji M.,National Research Institute of Aquaculture | Higano J.,National Research Institute of Aquaculture | Hasegawa N.,National Research Institute of Aquaculture | And 11 more authors.
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2014

Histological observations of the adult gonad and monitoring condition factor of the Manila clam Ruditapes philippinarum were performed using samples collected from northern (Hokkaido), central (Kanagawa, Aichi, Mie) and southern (Kumamoto) areas in Japan from April 2010 to November 2012. Many clams could not be defined definitively by one reproductive stage. When more than one developmental stage was evident within a single individual, the clam was assigned to all the reproductive stages that were observed in the tissue section. The reproductive stages were expressed by frequency of the stages that was noted for each sample group. Histological examination revealed that the spawning period was in summer at two sites in Hokkaido, whereas spawning began in spring and continued throughout summer until autumn, with two peaks in spring and autumn at the other four sites. While maximum and minimum condition factors in Hokkaido were attained in August 2010 and October 2010, respectively, those in the other sites were achieved in April 2011 and December 2011, respectively. Source

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