The Periodical Appearance of Bigger Migrated Kokanee at the Lake Chuzenji.

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By examing the body length of migrated spawning kokanee, <I>Oncorhynchus nerka</I>, in relation to environmental factors in the lake Chuzenji from 1983 through 1991, we found that the bigger fish appeared in every five or six years.<BR>Multiple regression analysis was calculated with predictor variables and criterion variables. The predictor variables are the following; total amount of influent in year, mean level of pondage in year, mean water temperature, number of stocking juvenile kokanee, body weight of stocking juvenile and biomass of crustacean. The criterion variables are length of mode of adult kokanee migrated after 2 years. The result showed that the appearance of bigger fish which formed the mode of body length composition was influenced by the biomass of the bait crustacean at the year juvenile kokanee were stocked, and not by the size of stocked kokanee. The decrease of amount of influent cause the rise of water temperature, and increase of the amount of crustacean. When total amount of influent at the stocked year increased, the stocked kokanee showed a higher survival rate. Consequently, many adult kokanee return to the mother river after two years. The result suggested that the increased number of migrated adult kokanee and the growth of body size in the Lake Chuzenji were density-dependent effects.
日本水産増殖学会の論文