Since the 1990s, the harvest of Manila clams Ruditapes philippinarum has decreased in one of the main fisheries areas on the eastern coast of Ise Bay. Furthermore, there were less than 400 tons in 2014, and it has decreased to 1 ton or less after 2016, which is similar to the successive tendency for the decrease harvests nationwide. Various factors have been considered about the nationwide decrease of Manila clams, but the causative factors remain to be verified. Recently in Ise Bay, the analysis using the individual growth model revealed the association of the decrease of Manila clams and a drop in the quantity of phytoplankton. However, the conclusions may have been influenced by the characteristics of the models that were used. Therefore, using three different individual growth models, I examined the reproducibility of the models as an index for the growth and mortality of Manila clam on the Kosugaya tidal flat, eastern coast of Ise Bay. As a result, the Shiba model and DEB model were able to reproduce the growth and mortality in the parameters based on the published papers. On the other hand, the Turushima model was able to reproduce the growth and mortality by resetting the parameter level with values determined from field observations. It was shown that the growth model is an effective tool to analyze the relation between the reduction in stock resource of Manila clam and the food environment in Ise Bay.
This study aiming to perform a discussion about the transformation a secular variations, and the shore erosion before and after the typhoon passage at the Shimizu Coastal Area by using UAV (drone) photographs acquired the period from 2017 through 2019. We performed the interpretation using orthogonal images during the distance of 1,015 m between the reference points of No. 43 through No. 52 determined by Shizuoka Prefecture Civil Engineering Office. As the results, as for the state of the shore erosion, it was revealed that any secular variation of beach line was not found. It is thought that this status are given by the effects of every year maintain to put the sand bypass and set the headlands by the government of Shizuoka. As for the shore erosion was found before and after the passage of the typhoon. However, there were cases where coastal erosion was not occurred depending on the typhoon.
We intend to continue this investigation to the future to estimate the sediment and erosion sand capacities to evaluate and consider the current artificial measure.
The brown macroalga, Sargassum horneri, is now attracting attention not only as a food source but also with regard to coast environmental preservation, coastal ecosystems, CO2 fixation, and as a marine indicator for environmental impact assessment. The present study was conducted to identify the effects of decreased seawater pH on S. horneri growth at three early developmental stages: embryo, germling, and young plant. After being exposed to acidic seawater of pH 6.0–7.5 for approximately 1–5 days, S. horneri embryos could germinate and grow when cultured in seawater with pH 8.0. At the germling stage, S. horneri growth was significantly inhibited when cultured in seawater with pH 6.0–6.6 compared to its growth in seawater with pH 8.0 (control). Moreover, at the young plant stage, S. horneri growth was significantly inhibited when cultured in seawater with pH 7.0 compared to when cultured in seawater with pH 7.5–8.0. These results demonstrate that the effects of decreased pH differ depending on the early growth stage of S. horneri, and as the growth of S. horneri progresses, the adverse effects of low pH increase. The results of this study can be used as preliminary data to promote S. horneri aquaculture in coastal areas and to assess the environmental impacts on its growth.
The Japanese giant perch (Lates japonicus) is one of the most mysterious fish in Japan. Its Japanese name “Akame” means red eye and the eye glows underwater exactly like a ruby. The fish mainly distribute along the Kochi and Miyazaki Prefecture coast and grow more than 130 cm over a period of 20 years. To monitor the behavior in the ocean, four adult Japanese giant perch were attached with archival tags and released along the Kochi coast. One individual was recaptured 696 days after release and its swimming depth, ambient water temperature, body temperature and light level were obtained every one minute. The trajectory from release to recapture was estimated using the light level. The fish was estimated to swim around the ocean. Vertical movements calculated from the swimming depth were analyzed using relative entropy techniques to detect the specific behavior. The relative entropy marked the maximum value on 22 June 2012 when the fish swam in deep and warm water considering the Kuroshio current. These results indicate that Japanese giant perch migrate between the Tosa and Satsunan area.
To understand the water quality environment and red tide generation mechanism in Tokyo Bay, it is necessary to monitor meteorological parameters related to photosynthesis not only along the coast of Tokyo Bay but also in the central part of the bay. Here, we report the observation data by meteorological instruments installed at the Umihotaru Parking Area.
Concerning the selection of places of Imperial Naval Bases, the survey team led by Lieutenant Commander Kimotsuki carried out hydrographic surveys at Kure and Sasebo in 1883. Although these surveys were conducted without any supports from naval vessels, it is misrepresented that a warship “Dai-Ni Teibou” led by Lieutenant Commander Togo brought the survey team to the sites and supported the hydrographic surveys.
This paper shows that the hydrographic surveys by the team led by Kimotsuki were conducted completely separately from “Dai-Ni Teibou” based on the descriptions in the historical naval documents.
“Dai-Ni Teibou” certainly conducted a hydrographic survey in Omura Bay. But, it is thought that the result of the survey was probably not so reliable that the Hydrographic Office could not use for compiling nautical charts.