沖ノ鳥島海域における水産資源開発と海洋エネルギー利用のための海洋調査

Ocean Investigation for Fisheries Resources Development and Uutilization of Ocean Energy in the Sea Region Surrounding OKINOTORISHIMA

Creators Ueda Takahiro

Creators Nishida Tetsuya

Creators Ohara Junichi

Creators Tanaka Tatsuhiko

Creators Ura Keisuke

Creators Urata Kazuya

Creators Ikegami Yasuyuki

An assessment of the nutrients, ocean resources, and ocean environment, which are vital to fisheries resources, is essential to preserve the fisheries resources in the vicinity of Okinotorishima. However, not many continuous investigations have been conducted. For the development of fisheries resources and utilization of ocean energy, an oceanographic investigation was conducted by the training ship Koyo Maru of the National Fisheries University. The investigations were carried out on the 9th and 10th of January, 2006 and the survey parameters consisted of, water depth, seawater temperatures at various depths, salinity, dissolved oxygen level, and water nutrients at various depths. The results were as follows: 1) The seawater temperature was approximately 24 ℃ at each observation point and decreased sharply to approximately 18 ℃ at a depth of approximately 200 m. At depths greater than 200 m, seawater temperature decreased gradually and 5 ℃ was recorded at 1000 m. The temperature difference between the surface and a depth of 1000 m was approximately 19 ℃ at each observation point. 2) High salinity levels from 34.7 to 34.9 PSU were observed from the surface to depths near 400 m. The salinity levels decreased to about 34.2 PSU near depths of 700 m. The salinity from depths greater than 700 m showed a tendency to increase. 3) The observation result showed that the amount of silicate around the surface was small. Therefore, it is possible to increase the number of diatoms (phytoplankton) by upwelling deep seawater and releasing silicate-rich water at the surface. 4) The phosphate levels at the surface ranged from 0 to 0.07 μmol/l. The level increased sharply until a depth of 500 m and was about 1.7 μmol/l at a depth of approximately 1200 m. The phosphate at depths greater than 1200 m exhibited a tendency to decrease. This tendency was similar to that observed in the case of silicate.

[ISSN]0370-9361