Studies on a Coastal Environment Management Method for an Open-type Bay： the Case of Shizugawa Bay in Southern Sanriku Coast

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  • 開放性内湾を対象とした沿岸環境管理法の研究：南三陸志津川湾の例
  • カイホウセイ ナイワン オ タイショウ ト シタ エンガン カンキョウ カンリホウ ノ ケンキュウ : ミナミサンリク シズガワワン ノ レイ

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Abstract

The Satoumi approach is a coastal environment management method consisting of ensuring thick, long, and smooth material flow and conducting fisheries that do not damage marine environments through optimal human interventions. Aquacultures are active in rias open-type bays that connect directly to the ocean with good water exchange between the bays and the ocean, which strongly influences the bays. Shizugawa Bay is one of the bays located along the Sanriku Coast. We have conducted studies on the development of a coastal management method using the Satoumi approach. Using satellite remote sensing, we investigated temporal changes in spatial distributions of seagrass and seaweed beds as feeding and spawning grounds for many marine organisms. Seaweeds have disappeared to leave barren rocky substrate since 2014, although heavy damage to seaweeds by the huge tsunami of The Great East Japan Earthquake was not observed in 2011. This is because fishermen stopped using a sea urchin fishery for three years after the tsunami. Sea urchins Strongylocentrotus nudus spawned in summer of 2011 were successfully recruited in2014and started to feed massively on the seaweeds. This fact shows that sea urchin fishery is a Satoumi activity to maintain seaweed beds. We measured loads of nutrients, dissolved iron, and particle organic matters from rivers, their standing stocks in the bay and their inflow and outflow between the bay and the ocean through the bay mouth in four seasons to clarify the material flow of the bay. Forests do not contribute sufficiently to primary production in the bay through material flow, although it is said that the forest is a lover of the sea. A decrease in oyster rafts as a Satoumi activity brought better growth of oysters and marine environments. At present, we organize “the Council for future environment in Shizugawa Bay” consisting of local fishermen’s cooperative branches, scientists, officers of Miyagi Prefecture and Minamisanriku Town, and WWF to realize sustainable fisheries and healthy marine environments through examining the number of aquaculture facilities and their deployment and marine environments based on data. Results and experiences obtained by this study will be applicable for other rias opentype bays.

Journal

  • Bulletin on Coastal Oceanography

    Bulletin on Coastal Oceanography 56 (1), 21-29, 2018

    Coastal Oceanography Research Committee, the Oceanographic Society of Japan

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