Nippon Suisan Gakkaishi 73 (6), 1042-1048 (2007)

Vertical distribution survey of the giant jellyfish Nemopilema nomurai by an underwater video camera attached to a midwater trawl net

NAOTO HONDA* AND TOSHIHIRO WATANABEa

Fishing Technology Division, National Research Institute of Fisheries Engineering, Fisheries Research Agency, Kamisu, Ibaraki 314-0408, Japan

Recently, the mass appearance of the giant jellyfish Nemophilema nomurai has caused serious damage to Japanese fisheries. To reduce the damage to fisheries, it is necessary to understand the distribution and behavior of the giant jellyfish in detail. The vertical distribution of the giant jellyfish was investigated using a midwater trawl net with an underwater video camera and depth loggers. The cod end of this midwater trawl net was opened so as not to capture the giant jellyfish, because the giant jellyfish is too huge to capture and its body would easily choke in the mesh of the net. The midwater trawl net was operated at approximately 100 kilometers off the west coast of Noto Peninsula in the Sea of Japan. Almost all giant jellyfishes were in the surface water shallower than approximately 40 meters depth in the daytime.


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