| Co-Investigator(Kenkyū-buntansha) |
TAKATSU Tetsuya Hokkaido Univ., Grad. School of Fish. Sci., Inst., 大学院・水産科学研究科, 助手 (50241378)
NAKATANI Toshikuni Hokkaido Univ., Grad. School of Fish. Sci., Asso. Prof., 大学院・水産科学研究科, 助教授 (80188979)
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| Budget Amount *help |
¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2001: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2000: ¥700,000 (Direct Cost: ¥700,000)
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| Research Abstract |
To clarify the survival strategy of larval and juvenile marbled sole Pleuronectes yokohamae, spatial and temporal distributions, food abundance in environment, feeding strategy, growth pattern, and predation were investigated in the coastal area of Tsugaru Strait.
1. A northward-inshore compensatory drift of deeper water in Hakodate Bay was induced by strong wind in March. Larvae would be transported from the offshore spawning ground to the inshore nursery area by this compensatory drift. Eye-migrating larvae settled mainly on 3-15 m depth bottom, and juveniles concentrated at 5m depth.
2. Initial foods of larvae were tintinnids and rotifers, and then shifted to copepod nauplii. Feeding success depended on water temperature rather than prey densities. Eye-migrating larvae shifted their main foods from cladocerans to harpacticoids. Low feeding intensity of these larvae would be caused by rapid changes in morphology.
3. Biased feeding on adult males of harpacticoids might have been caused by a behavioral difference in harpacticoid sexes. The main food organisms of juveniles (> 30 mm in standard length) changed from harpacticoids to benthic gammarids, cumaceans, tanaidaceans, and polychaetes.
4. Larvae and juveniles were swallowed by a shrimp Crangon uritai. The vertical distributions of these two organisms were more overlapped during the cold spring, increasing the opportunists for predation. This phenomenon seemed to be one of the causes of the interannual fluctuation in recruitment.
5. In rearing tanks, C. uritai fed on juveniles at night. Relative high abundance of Nipponomysis sp. would restrict and reduce the predation on juveniles by C. uritai in field
6. Growth rings in otoliths were validated as daily increments.
Large biomass of marbled sole would be sustained in the strong current, due to demersal and adhesive eggs, larval metamorphosis at small size, and warming by Tsugaru Warm Current. Further investigations needed to assess various mortalities quantitatively.
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