| Co-Investigator(Kenkyū-buntansha) |
UEDA Hirosi Hokkaido University, Faculty of Fisheries, Associate Professor, 水産学部, 助教授 (00160177)
TAKADA Takenori Hokkaido Tokai University, School of International Cultural Relations, Professor, 国際文化学部, 教授 (80206755)
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| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2000: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1999: ¥2,800,000 (Direct Cost: ¥2,800,000)
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| Research Abstract |
We investigated on carrying capacity and population density-dependent effect of Pacific salmon in the North Pacific Ocean. 1) The carrying capacity, which is calculated by the Logistic equation and the reproduction curve, of pink salmon in the North Pacific Ocean significantly correlated with the Aleutian Low Pressure Index (ALPI). This indicates that the carrying capacity of Pacific salmon may vary with long-term climate change. 2) Body size of Hokkaido chum salmon at maturity showed a significant decreasing trend from the late 1970s to early 1990s and relative increasing trend since the late 1990s. In Hokkaido chum salmon, not only significant negative relationship between population abundance and fork length, but also positive relationship between population size and average age at maturity of cohorts were observed. Growth analysis back-calculated from scales showed that a growth reduction occurred after the second year, especially in the third year of oceanic life of Hokkaido chum
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salmon. The recent growth reduction, however, had no significant effect on their fecundity and egg size. This suggested that reduced growth and increasing age at maturity were due to density dependent intraspecific competition and high abundance of chum salmon in the North Pacific Ocean. 3) In the Gulf of Alaska, a dominant prey animal of Pacific salmon except for chum salmon, which fed mainly on gelatinous zooplankton, was squids (mainly Berryteuthis anonychus) during years from 1994 to 1996, and 1998. In 1997, Pacific salmon was affected feeding and growth by the El Nino Event, and squids disappeared from their stomach. There is no difference of food niche among 6 species of Pacific salmon in the Gulf of Alaska since 1999, because all species fed mainly on zooplankton such as euphausiids, amphipods, copepods, and pteropods. The result of stable isotope analysis showed that trophic levels of nekton-feeders (e.g., coho and Chinook salmon, and steelhead trout) were higher than those of plankton-feeders (e.g., sockeye, chum, and pink salmon). 4) These results were published on many scientific papers, and presented at international symposium and meetings. Less
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