Studies of the population dynamics of edible giant jellyfish in relation to environmental changes in Ariake Sea

九州西部的有明湾有两种可食用的巨型水母，Rhopilima eschulentum（当地称为Akakurage）和R. hispidum（称为Shirokurage），传统上它们被收获并加工成食物。尽管鳍类和贝类的捕获量明显减少，但这些水母的捕获量相对稳定，近年来呈上升趋势。本研究的目的是阐明这些水母的种群动态与近期海湾环境因素的变化有关。自2005年另一种巨型水母Nemopilema monural首次出现在该海湾以来，对其动态也进行了研究。(1) 2001 - 2006年柳川鱼市海蜇年销售量，海鞘海蜇（加工湿重33-45吨）明显少于海鞘海蜇（加工湿重115-526吨）。与2001 ~ 2004年（115 ~ 285吨）相比，2005年（526吨）和2006年（447吨）大幅增加。(2) 4 - 5月放出幼体，7月生长为湿重20-30公斤的水母，8月达到最大值（约30-40公斤）。它们在九月性成熟。(3) 2006年在有明海发现了2只野村水母，第1只出现在7月10日（钟径60 cm），第2只出现在8月1日（钟径80 cm），表明该物种可能在有明海浅水湾建立了生活圈。(4)新鲜海蜇平均含水量为95%，加工海蜇平均含水量为87%。碳、氮含量分别为干重的15%和3.5%。

The Ariake Bay, western Kyushu, harbors two edible giant jellyfish species, Rhopilima eschulentum (locally called as Akakurage) and R. hispidum (called as Shirokurage), which have traditionally been harvested and processed for food. In spite of remarkable decrease in catch of fin-and shell-fish catch, the catch of these jellyfish are relatively stable and show an increasing tendency in recent years. The objective of this study is to elucidate the population dynamics of these jellyfish in relation to recent changes in the environmental factors of the bay. Since another giant jellyfish Nemopilema monural appeared for the first time in the bay in 2005, its dynamics is also investigated.(1) According to the annual amount of jellyfish on sales of Yanagawa Fish Market between 2001 and 2006, R. hispidum was mach fewer but stable (range: 33-45 tons of processed wet weight) compared to R. eschulentum (range: 115-526 tons). The latter showed a remarkable increase in 2005 and 2006 (526 and 447 tons, respectively) compared to 2001-2004 (115-285 tons).(2) Their ephyrae are released in April-May, grow to medusae of 20-30 kg in wet weight in July, and attain the maximum (ca. 30-40 kg) in August. They sexually mature in September.(3) In 2006, two N. nomurai medusae were confirmed to occur in the Ariake Sea, the first one on July 10th (bell diameter : 60 cm) and the second one on August 1st (bell diameter : 80 cm), suggesting that this species may establish the life cycle in this shallow bay.(4) The water content of fresh jellyfish is, on average, 95% and that of processed jellyfish is 87%. The carbon and nitrogen contents are 15% and 3.5%, respectively, of dry weight.