1Fukui Fisheries Experiment Station, Tsuruga, Fukui 914-0843, 2Japan Sea National Fisheries Research Institute Fisheries Research Agency, Chuo, Niigata 951-8121, 3Faculty of Fisheries, Nagasaki University, Nagasaki 852-8521, Japan
The body hardness of the giant jellyfish Nemopilema nomurai was investigated for the development of a jellyfish crush device using samples collected with set nets in Mihama Bay, Fukui Prefecture, during November 2007- January 2008, when a mass appearance occurred. The diameter of the umbrella and hardness of each jellyfish was measured on the top (apex of bell), periphery (bell margin) and middle regions of the umbrella (mainly the underumbrella) with a fruit sclerometer. No significant relationship between the diameter of the umbrella and the hardness of the underumbrella was observed. The hardness of the bell margin increased from 50 to 80 N/cm2 after December, being significantly higher than those of other regions, while the middle regions showed the lowest hardness. As for the exumbrella, its bell margin also had the highest hardness and was not different from the underumbrella in the same individual.