| Co-Investigator(Kenkyū-buntansha) |
NISHIKAWA Jun The University of Tokyo, Ocean Research Institute, Research Associate, 海洋研究所, 助手 (10282732)
NISHIDA Shuhei The University of Tokyo, Ocean Research Institute, Associate Professor, 海洋研究所, 助教授 (70134658)
TANABE Shinsuke Ehime University, Center for Marine Environmental Studies, Professor, 環境科学研究センター, 教授 (60116952)
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| Research Abstract |
Through the organic matter transport process of diel vertical migration by zooplankton and micronekton, the so-called "Biological pump", considerable amounts of anthropogenic pollutants such as organochlorines and organobutyltins may be carried into the deep-sea, especially into mesopelagic ecosystems. Myctophid fishes are one of the main components of the biological pump, since their biomass has been estimated in the order of one billion tons throughout the world's oceans and most of them undertake diel vertical migration i.e. at dusk they migrate up to the upper 200 m to feed on zooplankton and return to the mesopelagic zone at dawn.
For this project we examined vertical distribution patterns of 13 species of myctophids in the transitional waters of the western North Pacific and grouped them into 1) surface migrants, 2) midwater migrants, 3) semi-migrants, 4) non-migrants. Thereafter, we studied the feeding habits of the 3 dominant species, Diaphus theta (midwater migrant), Stenobrachius leucopsarus (semi-migrant), and S.nannochir (non-migrant) and estimated their daily food rations. Organochlorines (PCBs, DDTs, CHLs, HCHs, HCB) and organobutyltins (TBT, DBT, MBT) accumulated in the 6 dominant species were analyzed in order to investigate the accumulation mechanisms from the view point both of vertical migration patterns and the feeding habits of each species. Almost 90 myctophid species occur in the western North Pacific and have various vertical migration patterns and feeding habits which are helpful when assessing the pollution process. That is, myctophids are a good index animal group for monitoring the pollution of deep-sea ecosystems because of their high abundances and wide habitat coverage.
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