Factors Affecting the Abundance of Pondsmelt, Hypomesus nipponensis Population in Lake Ashinoko.

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  • 芦ノ湖におけるワカサギ資源の変動要因

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Abstract

In order to clarify the factors affecting the abundance of Pondsmelt population in Lake Ashinoko (35°12'N, 139°E), we investigated the date of hatching, growth rate, and the age composition of pondsmelt. In addition, we estimated the seasonal and annual losses of pondsmelt due to predation by fish species present in the lake such as rainbow trout, brown trout, and largemouth bass. The results are summarized as follows:<BR>(1) It was revealed from the estimation of the date of hatching and the growth rate of pondsmelts collected in the lake that the fish originating from released eggs were more frequent than those from spawnings.<BR>(2) The 1+ age fish were dominant among pondsmelt caught by gill nets. This suggests that recent declines in the gill net catch may be chiefly caused by poor survival of the 1+ age fish.<BR>(3) The estimated loss of the pondsmelt due to the predation by other fish exceeds that due to the fishing. Likewise the percentage of pondsmelt in the diet composition of largemouth bass remarkably increased in recent years; this suggests an increase in predation pressure by the largemouth bass.<BR>Overall, these results indicate that predation is a crucial factor determining the abundance of pondsmelt in the lake.

Journal

  • Aquaculture Science

    Aquaculture Science 43 (1), 1-9, 1995

    Japanese Society for Aquaculture Science

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