| Project/Area Number |
62560181
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
General fisheries
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| Research Institution | Hokkaido University |
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Principal Investigator |
MAEDA Tatsuaki Hokkaido University, Faculty of Fisheries, Professor, 水産学部, 教授 (00001595)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAGI Shogo Hokkaido University, Faculty of Fisheries, Instructor, 水産学部, 助手 (60179421)
NAKATANI Toshikuni Hokkaido University, Faculty of Fisheries, Instructor, 水産学部, 助手 (80188979)
TAKAHASHI Toyomi Hokkaido University, Faculty of Fisheries, Associate Professor, 水産学部, 助教授 (40002349)
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| Project Period (FY) |
1987 – 1989
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| Project Status |
Completed (Fiscal Year 1989)
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| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1989: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1988: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1987: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Keywords | Walleye pollock / Northern Japan Sea / Fishing and hydrographic conditions / Fish migration / Size composition / Vertical distribution / Dominant year class / 海況 / 魚群の分布回遊 / スケドウダラ / 分布回遊 |
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| Research Abstract |
To elucidate the population structure and migration of walleye pollock, Theragra chalcogranna, in the western coastal area of Hokkaido, sampling surveys were conducted in Japan Sea from Shiribeshi to Aomori Prefecture from April 1987 to October 1989 . Distribution of walleye pollock was observed by echo surveys and mid-water trawling. Zooplankton was collected by vertical hawls with Norpac net from 500 m depth to the sea surface. Hydrographic observations were carried out with CrD system. In February, tagging experiments were conducted to know the migration after spawning. Results are summarized as follows;
1. Shoal of Walleye pollock in April was found in 150-300 m depth near the spawning area, while in 200-400 m depth in the offshore area. Distribution of Walleye pollock expanded to the central area of Japan Sea, concentrating in the frontal zone between the Tsushima Warm Water and the Liman Cold Water.
2. Walleye pollock migrated to the shallower area in October with advancement of go
… More
nad maturation. In this period, they concentrated in deep layer from 400 m to 500 m, because of high temperature,
3. Population in this area was mainly constituted by 3-8 year classes and the 1984 year class dominated. The highest biomass of walleye pollock was observed in October, 1989.
4. The 2500 tagged fish were released from 1987 to 1989 in the coastal area of Hiyama. Results of recapture showed that walleye pollock migrated to the south from Toyama to Tsugaru Straight during the summer feeding season and retored in this study area prior to the spawning season. These suggest that they have strong homing instinct.
5. Formerly, it has been believed that walleye pollock migrated from the northern area (Musashi Bank) to this study area and returned after spawning. However, it was found that they migrated from southwestern area to the coastal spawning grounds. Prediction of population density requires further observations concerning the transport process of fish eggs and larvae, and ecology of immature fish. Less
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