| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2005: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
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.
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