BISAC NAT010000 Ecology
BISAC NAT045050 Ecosystems & Habitats / Coastal Regions & Shorelines
BISAC NAT025000 Ecosystems & Habitats / Oceans & Seas
BISAC NAT045030 Ecosystems & Habitats / Polar Regions
BISAC SCI081000 Earth Sciences / Hydrology
BISAC SCI092000 Global Warming & Climate Change
BISAC SCI020000 Life Sciences / Ecology
BISAC SCI039000 Life Sciences / Marine Biology
BISAC SOC053000 Regional Studies
BISAC TEC060000 Marine & Naval
Hiroshima Bay is located in western part of the Seto Inland Sea, and there is high productivity of Asari clam. However, the landings amount of the clam was rapidly decreased and production areas came to be limited in the northern part (bay head). Here, the clam has the planktonic larval stage. Then, it is important to reveal the transportation process of larvae to clarify the habitat connectivity of the clam. Therefore, in this study, we try to clarify the transportation process of the clam larvae in the Hiroshima Bay by numerical model experiments. As a result of model experiments, in June (rainy and heating season), the larvae are transported to southward in western area of Hiroshima Bay. In November (dry and cooling season), distribution of larvae is limited in the northern area of Hiroshima Bay. These results are corresponding to the field observation results. In the Seto Inland Sea, it is said that there is spawning time of the clam twice a year (spring and autumn). However, in a recent Hiroshima Bay, the density of the larva in spring is very low than that in autumn. These facts suggest that the production of the clam is limited in the northern area of Hiroshima Bay because the density of the larva is low in spring when the larvae can extend to the south.
Asari clam, decrease in landing amount of clam, transportation of larvae, habitat connectivity, numerical model experiment.
I. Introduction
Seto Inland Sea is semi-enclosed inland sea located in western part of Japan and the tidal flats develop. The landings amount of Asari clam (Ruditapes philippinarum) in this sea became the maximum in 1986 and this amount was about 1/3 of the entire Japan (shown in Fig.1). However, the landings amount rapidly decreased to 1/20 in the 1990's. Hiroshima Bay is located in western part of the Seto Inland Sea, and there is high productivity of Asari clam. However, the landings amount of the clam was rapidly decreased as well as the entire Seto Inland Sea and production areas came to be limited in the northern part (Fig. 2). Under these situations, various plans for the resource recovery were tried. However the amount of landings did not increase so much.
Here, the clam has the planktonic larval stage during three to four weeks. During this stage, it is considered that the clam larvae disperse about 20km-30km. Then, it is important to clarify the habitat connectivity of the clam to achieve the sustainable production. Therefore, in this study, we try to clarify the transportation process of the clam larvae in the Hiroshima Bay by numerical model experiments as the first step to clarify the habitat connectivity of Asari clam.
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2. Japan Coast Guard, “Tidal Harmonic Constants Table - Japanese Coast”, 1992.
3. Hamaguchi, M. “Progress report for project study of Agriculture, Forestry and Fisheries Research Council. -Techniques for sustainable development of coastal fishing by the restoration of ecological network-” 2013. (in Japanese)
4. Hamaguchi, M., Nagai, S., and Yasuda, N. “New methods to analyze meta-population dynamics. Gekkan Kaiyo, 37, 125-132, 2005. (in Japanese)
