びわ湖のホンモロコ個体群における変動要因の解析 V.0_+年魚における生長の年変動と越冬期における個体群の年変動との関係

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概要

• 論文の詳細を見る

• Whether the annual fluctuation of the yearling population of Gnathopogon caerulescens in winter is influenced by the fluctuation of growth of the under-yearlings was examined. Specimens for examining the size distribution of the under-yearlings were sampled from the fishermen's catches with a trawl net and trap from 1962 to 1967. The fishing was carried out by trawling in winter, and by trapping during the spawning season. The mean body length in early winter fluctuated annually from 5.75cm (1962 year class) to 6.59cm (1964 year class) and the coefficient of deviation fluctuated from 0.136 (1966 year class) to 0.156 (1962 year class). These results suggest that there is considerable annual fluctuation in the growth of the under-yearlings. Poorly grown individuals, smaller than approximately 6cm in body length, died between late winter and early spring every year (Fig. 1). This phenomenon reflects that the mean body length in early spring from 6.65cm (1965 year class) to 7.61cm (1964 year class) was greater than those in early winter and the coefficient of deviation from 0.075 (1964 year class) to 0.124 (1966 year class) was less than those in early winter. The survival rate in each year class in early spring was estimated by comparing the body length distribution of the under-yearlings in winter with those in early spring (the estimation method is shown in Fig. 3). These values fluctuate annually from 35.7 (1966 year class) to 57.0 (1965 year class) per cent. This fluctuation of survival rate seemed to be caused partly by the yearly differences of the growth rate up to the early winter and partly by the size specific survival rate. The index of number of the estimated survivors in early spring was computed by dividing the index of the biomass by the mean body weight of the under-yearling fish in winter and multiplying by the estimated survival rate. The index values of the estimated survivors and the actual ones showed almost parallel annual fluctuation. The correlation coefficient between the two index values was 0.882.

• 日本生態学会の論文

著者

• 牧 岩男

  和歌山大学教育学部生物学教室

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