Hearing survey from fishermen concerning seaweed communities on the Japan Sea coast of Aomori Prefecture, Japan
2018
Fujikawa, Y. (Aomori Fisheries Development Center, Regional Department of Agriculture, Forestry and Fisheries, Tou-sei Branch Office, Aomori Prefectural Government, Aomori, Aomori (Japan)) | Kirihara, S.
The hearing survey was conducted to clarify the present status and the changes in the last 10 years on seaweed beds and fishery organisms related to seaweed on the coast of Japan Sea, Aomori Prefecture, Japan. We interviewed the 29 fishermen at 21 coastal areas about the extents of sargassum beds, ISOYAKE caused by feeding of sea urchins, and the resources of sea urchin, top shell, abalone, edible algae, rockfish and sailfin sandfish in April and May 2017. As the result, it became clear that the extents of the ISOYAKE and the amount of sea urchin Mesocentrotus nudus remarkably decreased, while the extents of sargassum beds turned to increase on the Japan Sea coast of Aomori Prefecture. The amount of red/black rock fish which lives in sargassum beds, and of sailfin sandfish that spawn on sargassum also increased. Top shell and abalone which feed on seaweed increased especially on the southern coast. On the survey coast from 2010 to 2014, the highest water temperature exceeded 26degC as the lethal temperature of sea urchin, and in the same period its fish catch declined. The feeding behavior of Mesocentrotus nudus prevents the growth of seaweeds and is known as the main sustained factor of ISOYAKE along the coast of Aomori Prefecture. From these results, it was considered that the high seawater temperature in the summer that continued for several years would have contributed to the reduction of ISOYAKE and the expansion of the sargassum beds.
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